Abstract:
A general purpose computing machine utilizing a hardware executive system controller for reducing software system overhead. The computing machine has a uniprocessor embodiment which enhances system throughput and a multiprocessor embodiment which may be tailored to achieve a high level of concurrent processor operation. The computing machine utilizes a novel programming structure tailored to the machine architecture by separating data transformation tasks from control statements and performing the data transformation task at the processor level while performing the control task in the hardware executive.

Description:
TABLE OF CONTENTS 
     Field of the Invention 
     Description of Prior Art 
     (A) Enhanced Throughput 
     (B) Programmer Productivity 
     Summary of the Invention 
     Brief Description of the Drawings 
     Detailed Description of the Preferred Embodiments 
     System Overview 
     Definition of Transition Machine 
     Model of Parallel Programs 
     Procedure Eligibility Determination 
     System Status Updating 
     Example Program 
     Model of Transition Machine Architecture 
     Example Program Execution 
     General Implementation Considerations 
     System Controller Functional Operation-General Description 
     Interrupts 
     Detailed Implementation 
     Processor/System Controller Interface 
     System Controller Functional Operation-Detailed Description 
     Entry Transition 
     Exit Transition 
     Load Transition 
     System Controller Detailed Component Design 
     Data Constructs 
     Procedure Eligibility Determination Logic 
     System Controller Detailed Component Design (continued) 
     System Status Update Logic Circuit 
     Synchronization and Control Logic Circuit 
     System Controller Internal Operation 
     Single Processor Transition Machine Architecture 
     Entry Transition 
     Exit Transition 
     Load Transition 
     Selected Alternate Implementation of the System Controller 
     System Controller to Support a Conventional Operating System 
     Functional Operation 
     Entry Transition 
     Load Transition 
     Appendix A 
     Appendix B 
     Appendix C 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is in the field of computer architecture and more particularly in the areas of parallel computers and multiprocessing systems. The invention enhances throughput via hardware support for parallel processing and operating system efficiency. Programmer productivity is also enhanced using a hardware supported unique software structure. 
     2. Description of the Prior Art 
     A. Enhanced Throughput 
     Parallel processing has been recognized as a valuable mechanism for increasing computational speeds by performing concurrent or parallel computations. Various degrees of parallelism have been achieved in computers having both single and multiple processing units. These prior art approaches to the concurrency objective may be categorized into three broad areas: (1) implementation on a multitasking basis in a sequential processor, where concurrent processing paths are assigned priorities and compete for single stream resources; (2) implementation using special purpose hardware with multiple processors based on the concurrency requirement of the problem; and (3) implementation using a general purpose multiprocessor with a multiprocessing operating system to control it. 
     In the single processor multitasking solution, a single processor and its associated resources are time shared by programs running &#34;concurrently&#34; under the control of a multitasking operating system. The processor is required to provide (over any appreciable period of time) the processing power sufficient to accommodate the requirements along all paths plus the software overhead to multiplex between paths. In addition to assuring that all paths can be accommodated over any appreciable time interval, assurance must be provided for meeting the response time of each path in a worst case concurrency situation. The problems of meeting these requirements are compounded by operating system efficiency considerations. As a consequence, the processors must be sized to the specific problem with the capability of modular extentions typically not being accommodated other than by oversizing the processor to begin with. 
     In the special purpose multiprocessor approach, a computer is constructed based on a specific concurrency requirement. Examples of special purpose parallel computers that have been built are array processors such as the ILLIAC IV, STARAN I, SOLOMON II. These computers require large amounts of special purpose hardware, special programming structures, and are specially suited for problems involving large amounts of homogeneous parallelism such that identical operations are to be performed on multiple data items. Array processors allow multiple identical operations to be performed in parallel, thereby supporting the concurrency requirement. However, homogeneous parallelism represents a very small part of the parallelism present in computer programs, and therefore these special purpose computers are not typically suited to support the more general heterogeneous parallelism present in typical computer programs. 
     The multiprocessor with a multiprocessing executive is an attempt at a general solution which accommodates heterogeneous parallelism in modular increments. These solutions, however, are fraught with increasingly diminishing returns as the number of processors is increased. The reasons for the reduction in computing gain in a multiprocessor system are two fold: first, there is a large overhead associated with the software implementation of the single unified control mechanism in the operating system, and secondly, it is difficult to effectively exploit the high level (job or task) of parallelism in application programs. 
     These two problems have aggravated each other since the large overhead has been taken as the justification for the high level modeling of parallelism but by exploiting parallelism at the job or task level, much of the potential gain of multiprocessing is lost since typically there is some amount of parallelism within the job or task and this internal parallelism cannot be exploited. 
     B. Programmer Productivity 
     Programmer productivity has been cited as a major cost problem on automated data processing (ADP) systems. Software development and maintenance costs have continued to climb in the same era of drastic reductions in hardware costs. Structured programming and other disciplines have been defined to reduce the problem. Unilateral agreement among proponents of these disciplines seems to exist in four areas of concern relating to the structure of programs and the computer architectures to which they apply: 
     (1) a requirements-oriented structure; 
     (2) a structure for which only the essential aspects of program control must be specified by the programmer; 
     (3) a structure which eliminates transfers of control (GO TO, CALL, queueing requests, etc.); and 
     (4) a structure which simplifies the error-prone aspects of decision logic. 
     The significance of each of these requirement areas is discussed below. 
     Requirements-oriented Programming 
     The specification of program requirements and the translation of these requirements into program design data is a major program development activity. One reason that these development activities require such a large percentage of the overall development process is because of the incongruities between the typical situation/response nature of program requirements and the procedural implementation of these requirements in the final design. Thus, there is a major translation from requirement to design which is a timeconsuming, error-prone process. Once the design has been established and implemented, it no longer resembles the structure of the requirements. The gulf between requirements and program design in conventional architectures hampers program understandability and therefore documentation, maintainability, etc. Thus, it is typically impossible to verify that a program of any magnitude actually implements its requirements. 
     Elimination of Degeneracy 
     In the conventional software framework the programmer typically translates the computation requirements into a somewhat arbitrary sequence of actions to be performed by the machine. In many cases, however, there is no sequence of actions implied in the requirements, so a sequence is artifically induced by the programmer. Thus, variant &#34;correct&#34; program versions can exist with entirely different structures. These programs are degenerate solutions to the problem described by the requirements specification. In essence the programmer has the ability to induce his own design philosophies and personal preferences into what would idealy have been an objective translation of a requirement that could have been directly compared with other versions. This design indeterminacy has the effect of making the implementations less directly relevant to the requirements such that verification must be performed only at the lowest level to determine that the final result does in fact meet the requirement. 
     Exploitation of the parallelism inherent in the computation is also precluded by arbitrary determination of execution sequence. This arbitrary determination reduces program effectiveness in parallel processing environments. The inherent relationships between program segments is also obscured such that later program maintenance is more likely to induce errors. 
     Thus, by requiring only the essential aspect of program control, the requirement translation process is simplified, many of the previously arbitrary decisions on sequence made by the programmer are eliminated, and exploitation of parallelism is supported. 
     Eliminating Direct Transfers of Control 
     The direct transfer of control is recognized as the major source of programmer coding errors. Many of the developments in software engineering have been directed to the elimination of these structures from programs. The result has enhanced software productivity, but since these structures are still supported to varying degrees in compilers, and unilaterally at the machine level, many errors can still be attributed to them. Conventional executive requests to execute a specified program are also GO TO&#39;s, the only difference being that they are implemented at a high level. 
     The executive request problem is an interesting one in that a program could be completely correct but not be executed under the right conditions because it was incorrectly requested. Thus, there is an intricate coupling between programs. There is also the possibility of a totally unsuspected program requesting the execution of a program for a completely inappropriate situation. Therefore, before a program can be completely verified to meet its requirements every set of conditions under which it can be requested must be known. 
     Simplification of Decision Logic 
     The elimination of GO TO&#39;s is significant from an error-proneness point of view, but decision logic structures are very major offenders also. Decision diagramming has been used to address some of the error proneness of these logic structures, but they are a monitoring and evaluation tool not implemented as a part of the program structure in the design, and thus their use constitutes a divergence (additional effort) from the central development path. 
     The typical decision logic constructs involve a transfer of control which therefore allows circumvention of GO TO-less dogmas at the detailed implementation level. They also have the feature of treating program activation conditions as disjoint, without global awareness. A particular test for a&lt;b, for example, may only be executed if a&gt;c, d&lt;e . . . . But this total situation is not readily apparent to the programmer writing/reviewing the code. Therefore, very complex meshes of logic may be implemented to provide assurance of the specific conditions of execution which, because of a decision higher in the structure, preclude a program&#39;s ever being executed. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to overcome the disadvantages of the prior art by providing a hardware executive apparatus incorporating an event-driven structure for use with a uniprocessor or a multiprocessing system. 
     Another object of the invention is to provide improved throughput of a computing system by eliminating software overhead functions and incorporating same into a hardware implementation. The hardware implementation incorporates the utilization of a system status vector and a relevance matrix. The status vector and relevance matrix are utilized for enabling data transformations in a multiprocessing environment resulting in a high level of concurrent operation. 
     In accordance with another aspect of the invention, there is disclosed a computation structure for which there is a direct traceability to requirements. As a consequence, the invention achieves a tremendous increase in programmer productivity. Requirements are typically of the form: &#34;When a certain `situation` arises, perform an `associated function`.&#34; `Situations` are typically describable in terms of sets of conditions on parameters which are represented in the data base. The `associated functions` correspond to programs which change parameter values. 
     Yet another object of the invention is to provide a computing architecture having a data transformation aspect and a central control aspect thereby providing a structured computational environment for enhancing program use, development, documentation and verification. The central control aspect of the computational structure is characterized by WHEN statements involving a plurality of data conditions in the form of unary predicates on the data set. When the WHEN conditions are met, a data computation is enabled for execution in the data processor. In a multiprocessing system, a plurality of data transformations may be enabled for concurrent execution thus resulting in highly parallel system operation. The WHEN block structure is implemented in hardware which results in low overhead at the architectural level. 
     In accordance with the invention there is provided a hardware executive apparatus for use in a multiprocessing system for the concurrent operation of a plurality of data processors in solving an algorithm defined by a plurality of application programs and a control program. The data processors access application program memory storage means and data memory storage means and have at least a common data memory area accessible by the plurality of data processors. The hardware executive apparatus executes the control program and comprises a status storage means for storing global binary status indications S j  of a data set appropriate for solving the algorithm. The stored status indications correspond to data conditions which are relevant for enabling execution of application programs by the plurality of processors which are necessary in solving the algorithm. The hardware executive apparatus additionally comprises a relevance storage means for storing groups i of binary relevance indications R ij , each group corresponding to the relevance of the status indications to the i th  one of the application programs where i is an integer designating one of the groups and corresponding to one of the application programs and j is an integer designating one of the binary status indications. The hardware executive apparatus additionally comprises a means for updating the status indications stored in the status storage means at completion of execution of each application program, a means responsive to the relevance storage means and status storage means for determining the eligibility of the application programs for execution by the plurality of processors, and means for enabling execution of eligible application programs by the plurality of processors whereby application programs which are determined eligible may be executed concurrently. 
     The invention may also be characterized as a computing machine capable of transitioning between states for solving an algorithm and comprising a plurality of data processors each including computing means for computing data in accordance with an application program, data memory storage means having at least a portion thereof shared by the plurality of data processors, application program memory storage means for storing said application program, a hardware system controller operable for determining the eligibility of each of the application programs and for enabling operation of different ones of the data processors for concurrent execution of the eligible programs, and wherein the system controller is operable for determining eligibility based on a plurality of unary predicates associated with the applicability of the transition between states of said machine for solving said algorithm. 
     In accordance with another aspect of the invention, there is disclosed a method of increasing program throughput in a plurality of data processors forming a computing system comprising the steps of: (a) structuring the programming of an algorithm to be carried out by the computing system into a plurality of data transformation programs and a control program, the data transformation programs performing event-driven data computational steps without transfer of control to other transformation programs and the control program scheduling execution of the data computational steps, (b) selecting a plurality of unary predicates which collectively represent all data conditions relevant to enabling execution of all of the data transformation programs, the unary predicates forming status indications of said data conditions, (c) designating all of said unary predicates which are relevant to enabling the execution of each of the data transformation programs, the designated unary predicates forming a group of relevant indications corresponding to each data transformation program, (d) storing the data transformation programs in memory storage devices accessible by said plurality of data processors, and (e) storing the control program in a hardware executive apparatus. The hardware executive apparatus is effective for scheduling data transformation programs by including the steps of: (1) maintaining a memory store of the status indications, (2) maintaining a memory store of each group of relevance indications, (3) determining the eligibility of data transformation programs by hardware logical operations on the status and relevance memory stores wherein a data transformation program is determined eligible for execution if all status indications are true which are relevant in the group of relevance indications corresponding to the data transformation programs, (4) enabling the eligible programs wherein concurrently eligible data transformation programs are executed concurrently, (5) updating the memory store of the status indications upon completion of execution of each data transformation program, and (6) repeating steps (3)-(5) above until data transformation programs are no longer determined eligible whereby the algorithm is completed by the computing system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects of the invention will become clear in reference to the foregoing specification taken in conjunction with the drawings wherein: 
     FIG. 1 is a block diagram of the transition machine in accordance with the invention; 
     FIG. 2 is an illustration of the primary data constructs utilized in the system controller in accordance with the invention; 
     FIG. 3 illustrates an example program utilized in explaining the programming aspect of the transition machine in accordance with the invention; 
     FIG. 4 illustrates a conventional request driven program for solving the example problem of FIG. 3; 
     FIGS. 5A and 5B illustrate a request and event-driven program for solving the problem of FIG. 3; 
     FIG. 6 is a listing of an event-driven program for solving the problem illustrated in FIG. 3; 
     FIG. 7 is a program listing for an event-driven program with only assignment statements solving the program illustrated in FIG. 3; 
     FIG. 8 is a program listing for the transition machine program in accordance with the invention for solving the problem illustrated in FIG. 3; 
     FIG. 9 is an example of a partial program listing corresponding to FIG. 8 and illustrating requirements oriented programming techniques; 
     FIG. 10 is a table listing of control and data transformation programs corresponding to the requirements oriented programming technique of FIG. 9; 
     FIG. 11 is a mathematical representation of the major components and operation of the transition machine architecture in accordance with the invention; 
     FIG. 12 is an illustration of the R, T and F matrices corresponding to solving the example program in accordance with the invention; 
     FIG. 13 is a flow diagram that shows that various system states of the data constructs during execution of the example program; 
     FIG. 14 is a block diagram illustrating the data constructs of the transition machine together with basic elements of the interface in accordance with the teachings of the invention; 
     FIG. 15 illustrates a block diagram of the read, write and execute functions in accordance with the invention; 
     FIG. 16 shows a flow chart for the operation of a data processor and the system controller during various modes of operation of the transition machine; 
     FIG. 17 is a flow chart illustrating the interrupt operation in accordance with the invention; 
     FIG. 18 is an overall block diagram of the major components of the transition machine structure in accordance with the invention; 
     FIG. 19 is a block diagram of the multiport control aspect forming one embodiment of the transition machine; 
     FIG. 20 is a flow chart of the operation of the multiport control system of FIG. 19; 
     FIG. 21 is a flow chart showing the processor entry and exit operations in accordance with the invention; 
     FIG. 22 is a flow chart showing the processor load operations in accordance with the invention; 
     FIG. 23 is a flow chart showing the system controller entry, exit and load operations in accordance with the invention; 
     FIG. 24 is a block diagram of the data construct section of the system controller; 
     FIG. 25 is a schematic diagram of the procedure eligibility determination logic circuit of the system controller; 
     FIG. 26 is a block diagram of logic circuit nomenclature utilized in the drawings; 
     FIG. 27 is a schematic diagram of the system status update logic circuit of the system controller; 
     FIG. 28 is a block diagram of the input and output lines associated with the syncrhonization and control logic circuit of the system controller; 
     FIGS. 29A and 29B together form a detailed schematic diagram of the synchronization and control logic circuit of FIG. 28; 
     FIG. 30 is an illustration of the state diagram for use in implementing the synchronization and control logic circuitry; 
     FIGS. 31 and 32 are timing diagrams illustrating entry transitions in accordance with the invention; 
     FIG. 33 is a timing diagram illustrating an exit transition in accordance with the invention; 
     FIG. 34 is a timing diagram illustrating a load transition in accordance with the invention; 
     FIG. 35 is a block diagram illustrating the transition machine architecture for a uniprocessor in accordance with another aspect of the invention; 
     FIGS. 36A and 36B illustrate design language syntax listings describing the operation of the uniprocessor of FIG. 35; 
     FIG. 37 is a block diagram of a special system controller which supports an operating system in a uniprocessor environment; 
     FIG. 38 is a flow diagram of the processor logic required to activate the entry transition in the system controller of FIG. 37; 
     FIG. 39 is a flow diagram of the processor logic required to activate the load transition in the system controller of FIG. 37; and 
     FIG. 40 is a flow diagram of the system controller logic required to effect the load and entry transitions for the operating system in the processor of FIG. 37. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     SYSTEM OVERVIEW 
     Definition of Transition Machines 
     The family of computational machine architectures described herein implements a completely general model of parallelism. An overall block diagram of a computing system or, as termed herein a transition machine has made in accordance with the invention is shown in FIG. 1. The transition machine is seen to comprise a plurality of processors 2a, 2b, 2c each connected to a common memory 4. While only three processors are shown, it is understood that a large number of processors may be used including I/O controllers and other special purpose processors. (A single processor embodiment is also disclosed herein.) Further, the common memory 4 is typically composed of a plurality of memory modules 6a, 6b, 6c, 6d of which only four are illustrated. Each memory module may provide storage means for data as well as for application programs, or additional memory modules may be provided for such purposes as desired. For the multiprocessor embodiment, however, at least some data storage areas are made commonly accessible to the plurality of data processors. It is also understood that some of the processors may in fact be I/O processors or controllers connected in conventional; and fashion to one or more I/O devices. 
     A System Controller 10 is shown connected to the processors 2 via a processor/system controller interface 12. The System Controller 10 forms the heart of the invention and is more fully described hereinafter. In practice, the processors 2 and common memory 4 may be of conventional hardware design. The System Controller 10 is utilized, together with interface 12, to dispatch activities to the processors 2 and to achieve concurrent operation of the processors 2, in a multiprocessor system. The System Controller 10 is thus similar in function to a multiprocessor software system executive, but has the advantage of extremely low overhead. 
     Model of Parallel Programs 
     The abstract conceptual model of parallel computation is set forth the example in a number of articles by Robert M. Keller e.g. &#34;Formal Verification of Parallel Programs&#34;, Comm. ACM 19, 7 (July 1976) pp 371-384; &#34;Parallel Program Schemata and Maximal Parallelism&#34;, J. ACM 20, 3 (July 1973), pp 514-537; and J. ACM 20, 4 (October 1973), pp 696-710. 
     The conceptual model has been termed a transition system and is accepted as the basis for the more detailed architectural model set forth herein. A transition system is a model of the run time structure for computer programs; it is a form into which any &#34;structured&#34; program can be converted directly by a compilation process. The transition machine provides a machine architecture in which transition systems can be executed. 
     The transition system model is defined as (Q, →), where Q is the set of possible systems states and → is the set of transitions between states as described by Keller. A named transition system is a triple (Q, →,Σ). The components correspond respectively to the set of all possible system states (q 1 , q 2 , q 3 . . . ), a set of all transitions between states (→ 1 , → 2 , → 3 , . . . , ), and a set of names (σ 1 , σ 2 , σ 3 , . . . ) associated with groups of individually programmed transitions between states. Since there is a one-to-one correspondence between the indices on sigma and the names themselves, the indices can be used to indicate the names: i impliesσ i , and I.tbd.{i} implies Σ. The index i ε I is associated with a group of system transitions described by the statement: 
     
         when R.sub.i (d) do d&#39;=Ψ.sub.i (d) 
    
     The symbols in this statement are defined as follows: 
     i=the index of the group of transitions whose common feature is that they all result in the data transformation indicated by the function Ψ i   
     d=the set of all data items in the system 
     R i  (d)=the subset of satisfied propositions on the data set, d which are essential to defining the appropriateness of transitioning as determined by performing the data transformation Ψ i  (d). 
     Ψ i  (d)=the programmed functional data transformation (referred to as a subsystem herein) associated with the group of system transitions indicated by i which operates on the data set, d and results in a revised data set d&#39;. 
     The set i represent procedures (including enabling predicate) that can be written by a programmer to effect transformations Ψ i  on the data set d when the appropriate set of conditions R i  is satisfied on that data set. The Ψ i  are the individual program subsystems which constitute a computer program. In a parallel computation step multiple sets of conditions R i  are satisfied simultaneously such that multiple subsystems can be executed in parallel. R i  is an enabling predicate that indicates the requisite status of the data set which properly enables the execution of the subsystem which performs the transformation, Ψ i . Each of the enabling predicates R i  is made up of a set {R ij  }, j≦J of unary predicates where J is the total number of unary predicates required by the entire algorithm or computation problem. A unary predicate may be defined as a single proposition on the data set and thus represents a single data condition whose value may be specified in or by a binary indication, e.g. true or false. Propositions which are examples of unary predicates on the data elements e j  εd are the following: 
     (1) the data element e j  is available/not available for use in subsequent computations, 
     (2) the data element e j .sbsb.1 satisfies/does-not-satisfy a specified relation to some constant or other data element e j .sbsb.2 (for example, e j .sbsb.1 &lt;e j .sbsb.2), and 
     (3) the data element e j  can/cannot be updated. 
     The implementation of the conceptual model is carried out by reducing control over transitions between states to a mechanical operation. To achieve such control the set of states, Q is restricted such that only those which may imply a different set of eligible subsystems are considered to be unique. In making this restriction any particular state q can be signified by a set of binary status indications on a global set of unary predicates. The global set of unary predicates is restricted to include only those which are relevant to the eligibility of defined subsystems, i.e., the status of the data condition a&gt;b will be a significant part of q if and only if the condition a&gt;b is relevant to the eligibility of some subsystem, i. 
     Procedure Eligibility Determination 
     The eligibility of any particular subsystem, i can thus be determined by selecting the set of global unary predicates that are pertinent to initiating execution of the transformation d&#39;=Ψ i  (d), and by determining the status of those pertinent unary predicates. Thus the control over transitioning can be implemented by: 
     (1) maintaining a variable system status vector S whose components are binary status indications, one for each unary predicate in the global set, and 
     (2) maintaining for each subsystem, i a relevance vector, R i  of fixed indications for designating which of the global set of unary predicates are relevant for enabling a particular subsystem. 
     Once the sense of the indications in R i  and S have been defined, there exists a logical algebraic operation, &#34;·&#34; which can be defined such that E i  =R i  ·S, where E i  is a binary status indication of the eligibility of the subsystem, i. The set of vectors, R i  can be arranged as a matrix, R, the i th  row of which is equivalent to R i . The vector algebraic operation, &#34;·&#34; is then extended to include matrices such that: 
     
         E=R·S, 
    
     where 
     E is a vector indicating the eligibility status of every defined subsystem in the system. The relationship of the data constructs is shown in FIG. 2. A specific set of definitions and theorems relating the sense of the indications in R, S and E and the operations &#34;·&#34; is included as Appendix A. 
     System Status Updating 
     There is now a prescription for determining subsystem eligibilities (E vector) based on system status (S vector) and the subsystems&#39; conditional data requirements (R vector). There is now set forth a procedure for the computation of a new system status vector which is appropriate subsequent to the completion of a given subsystem. 
     There are several possible implications on the status of a data condition at the completion of a subsystem. They are as follows: 
     (1) The data condition remains unaffected by the subsystem running to completion; 
     (2) The data condition is satisfied whenever the subsystem runs to completion; 
     (3) The data condition is negated whenever the subsystem runs to completion; and 
     (4) The data condition is determined dynamically by the execution of the subsystem. 
     It should be noted that there are also implied modifications to system status at entry to a subsystem in the preferred embodiments to be described; these modifications prohibit the same transition from being attempted in multiple processors by denying subsequent update access to d&#39; when the transformation d&#39;=Ψ i  (d) is initiated. 
     The implications to system status at completion of a subsystem is readily accommodated by three data constructs. Two of these are fixed vectors (T and F) indicating respectively the always true (2 above) and always false (3 above) situations. For example, execution of a subsystem which is responsible for computing the value of a variable A would always result in the condition &#34;A available&#34; being set true. A third vector, V, is set dynamically (4 above) by the subsystem based upon the relationship of data variables computed by the subsystems. For example, the subsystem responsible for computing either of the variables A or B would have to return the status of the condition &#34;A&gt;B&#34; upon completion. It is clear that the updated status vector S can be computed as a function of T, F and V. The class of functions can be restricted by overlapping the defined sense of the fixed vectors T and F so as to provide a mask against unauthorized dynamic changes to S through the V vector. Appendix B provides a specific definition of the sense of T, F and V for a particular implementation. 
     A single vector construct A, is required to protect a procedure executing in one processor from being activated in another to perform the same data transformation in cases where this is inappropriate. A specific implementation of this construct is described in Appendix C. 
     Example Program 
     Before proceeding to describe the hardware implementation of the computational structure of the transition machine, an example program is described. This program describes how the software actually operates on a transition machine and a specific implementation of the S, R, T, F, A and V constructs (as described above and in appendices A, B, and C) for the example program. It is also shown how the requirements discussed under software productivity in the background section of the invention are supported by this computation structure. 
     FIG. 3 is a flow diagram of the example program to be used. For each block on this diagram, a high order language procedure is written to perform the requested function. Such a simple computation would not typically be broken into so many small subsystems, but this has been done primarily to give a clear example of how one can implement control flow with a unique computation structure. The function performed by the example set of programs simply computes the sum of the first twenty integers divided by twenty factoral. This function is not essential to the treatment and is given only to illustrate later how the conditions which effect control relate to the requirements of a computation. It is important to note the parallelism that is exploitable in this computation in that the product (block 3) can be computed in parallel with the sum (block 4). 
     In FIG. 4 the example program is implemented in a conventional request driven system. In this structure the flow control is completely implemented by active program requests. The control aspect of the program is interspersed with the data computation aspects. Because of this, any subsystem (program) can be activated by any other subsystem by a direct transfer of control, independent of the computational requirements it implements. Also, note that parallelism cannot be easily exploited due to the problem of trying to synchronize concurrent subsystems. The end effect is that this software structure does not support any of the identified requirements discussed above by way of background of the invention. 
     FIGS. 5A and 5B show the next stage in the example program evolution implemented in a system that supports both requests and events. In this system a subsystem may be activated based on a request by another subsystem or its activation may be determined based on a set of event flags being set appropriately. (It should be noted that these flags denote the status of unary predicates.) This provides a means for solving the synchronization problem that previously prevented parallelism from being exploited. Any subsystem can still request any other subsystem, and a direct transfer of control is still possible within this structure. Event based control structure allows the available parallelism to be easily exploited and therefore supports the requirement that only essential aspects of program control be specified by the programmer. A system that supports both requests and events represents the current state-of-the-art in operating systems. 
     FIG. 6 shows the next step which is a totally event-driven (data condition-driven) version of the program where the activation of every subsystem is based on the status of a set of required event flags. The overall system flowchart is this and subsequent examples is the same as that of FIG. 5B. This approach is not typically incorporated in current systems due to the high overhead involved in processing the large number of event flags in software. The advantage of this structure is that subsystem requests (inter-program direct transfer of control statements) can be eliminated. Control in this system is implemented by setting the appropriate event flags on completion of each computation. The result is a more requirements-oriented control structure in that the data conditions required to enable each subsystem are specified as an inherent part of the subsystem. Although &#34;FLAG0&#34;, &#34;FLAG1&#34;, etc., are not requirements-oriented, this is seen to be primarily a mneumonic problem where identifiers directly associated with specific requirements could have been assigned to the event flags. For example, Table I shows a possible assignment of mneumonic specifiers to the event flags which results in a very readable requirements-oriented structure. 
     
                       TABLE I______________________________________REQUIRED CONDITION MNEMONICS DEFINITIONSMNEMONIC           ASSIGNMENT______________________________________INITIALLY          FLAG0FACTORIAL.READY    FLAG1SUM.READY          FLAG2CONTINUE.FACTORIAL FLAG3CONTINUE.SUM       FLAG4COMPUTE.RATIO      FLAG5______________________________________ 
    
     The vent based structures allow easy exploitation of the available parallelism. There is still not a complete elimination of the direct transfer to control statements, however, in that the &#34;if then else&#34; statement in the subsystem PGM2 implies a transfer of control internal to the program as was discussed previously relative to decision logic. 
     FIG. 7 shows a totally event driven program with only assignment statements even for the implementation of what was formerly decision logic. This was facilitated by using logical operators to assign the status of event flags that are determined dynamically during the execution of subsystems. As a result, there is a complete elimination of the direct transfer of control structures. A very requirements-oriented control structure has resulted, and only the essential aspect of program control is required, with parallelism being easily exploited. 
     The programming structure utilized for the transition machine in accordance with the invention is illustrated in FIG. 8. An example of the source statements for this software structure is shown in FIG. 9 which illustrates the requrements oriented aspects of the structure. In this structure each subsystem is divided into two components: (1) a complete specification of the global conditions required to enable the subsystem (WHEN (list of conditions)), and a specification of the global conditions updated on completion of the subsystem (THEN (list of conditions)), and (2) a sequential set of data transformation statements. FIG. 10 shows the complete dichotomy of control and data transformations, and it is this computation structure that is implemented as the transition machine architecture. 
     Model of Transistion Machine Architecture 
     FIG. 11 shows a general characterization of the model of the transition machine architecture which implements the desired computer architecture. There are two major components of the machine. The first component may be termed a control component, and it maintains status indications for all the relevant global conditions (referred to as flags earlier) in the system. It also contains indicators associated with each subsystem specifying the subset of global conditions required to activate the specific subsystem and indicators specifying the modification to the global conditions implied on completion of the subsystem. The second component is a computation component which executes the code associated with the data transformation aspect of each subsystem. 
     In operaton, the control component first determines an eligible subsystem by examining the current status of the global conditions specified by each relevance indicator associated with each enabling predicate for the subsystem. The eligible subsystem is identified to the computation component which then executes the specified sequential arithmetic operations associated with the subsystem and returns status indications specifying the conditions that have been modified dynamically by the subsystem. The control component updates the global condition indications associated with having completed the subsystem. The cycle is then repeated until the system runs to completion. 
     Example Program Execution 
     FIG. 12 illustrates the operation of the computational structure exemplified by the architecture model by showing appropriate values for the defined constructs of the example program of FIG. 8. The assignments of subsystems and unary predicates to rows and columns of the constructs appropriate to the example are as follows: 
     A. The components of the system status vector, S, defined in Appendix A, are binary status indications of the unary predicates which have been represented as flags in the example program. Thus, for the example program, the assignment of unary predicates to components of S can be made as follows: S 1 , &#34;Initially&#34;; S 2 , &#34;Factorial.Ready&#34;; S 3 , &#34;Sum.Ready&#34;; S 4 , &#34;Continue.Factorial&#34;; S 5 , &#34;Continue.Sum&#34;; and S 6 , &#34;Compute.Ratio&#34;. 
     B. The relevance matrix, R, is defined in Appendix A. Each row in the R matrix is assigned to a subsystem. The assignments for the example program are as follows: Row 1, PGM 1; Row 2, PGM2; Row 3, PGM3; Row 4, PGM4; and Row 5, PGM5. Each column in the matrix is associated with a unary predicate with assignments corresponding to those for S. 
     C. The T and F matrices are defined in Appendix B. Each row of these matrices is associated with a subsystem with assignments corresponding to those of R. Similarly, the columns are assigned to unary predicates just as they are for R. 
     D. The V vector is defined in Appendix B. The binary status indicator components of V are assigned to correspond to those of S. 
     E. The A matrix is defined in Appendix C. The row and column assignments correspond to those of R. For the example, the values used for A correspond to R which is not necessary but sufficient to provide the needed protection for a multiple processor implementation. 
     FIG. 13 is a flow diagram that shows the states of the various constructs during execution of the example program. The operations causing the various state transitions are identified above the transition arrows. Each initial state is identified by a number. 
     The initial S vector for the example program is S=(1,0,0,0,0,0), indicating &#34;Intially&#34; is the only data condition currently true. By generating the dot product of the R matrix shown in FIG. 12 with the current S vector (as described in Appendix A), it is seen that only E 1  is non-zero at this time so that the only eligible subsystem is PGM1. An entry transition is initiated for PGM1 which is dispatched to a processor. This entry transition causes an update to the S vector (involving the A vector) which makes PGM 1 no longer eligible after entry and thereby precludes the inappropriate simultaneous execution of PGM1 in more than one processor. The system remains in this state (state 2) until PGM1 executes to complete and the appropriate exit transition is initiated at which time the system transitions to state 3. In state 3, only PGM2 is eligible. PGM2 is dispatched to the next processor requesting an activity. The appropriate entry transition is performed when PGM2 is dispatched, which puts the system in state 4 where again no subsystems are eligible. The system remains in the state 4 until PGM2 is complete, at which time the exit transition for PGM2 is initiated. On completion of the PGM2 exit transition the system will be in either state 5 or state 10. These are two states possible due to the variable (data value dependent) update returned by PGM2 as shown in FIG. 8. If the system is in state 5 then both PGM3 and PGM4 become eligible simultaneously. These two subsystems can be executed in parallel by separate processors. The state flow diagram in FIG. 13 shows PGM3 being dispatched to a processor and the system transitioning to state 6. PGM4, which is still eligible in state 6 is then dispatched to another processor and an entry transition to PGM4 is performed which puts the system in state 7. (The order in which these two subsystems are dispatched could be interchanged and the end effect would remain the same.) The system will remain in state 7 until either PGM3 or PGM4 runs to completion and the appropriate exit transition is performed. The order in which these subsystems complete is also unimportant, in that the end result will be the same in either case. The state flow diagram in FIG. 13 shows PGM3 completing first which causes the system to transition from state 7 to state 8 and then PGM4 completes which causes the system to transition from state 8 to state 9. In state 9, PGM2 becomes eligible again and the sequence is repeated. If on completion of PGM2 the system is in state 10, PGM5 becomes eligible. When PGM5 is dispatched the entry transition will put the system into state 11 and the system will remain in this state until PGM5 is completed. On completion of PGM5 the system will transition to state 12 which represents the end of the example program. No more transitions will take place until another set of constructs is loaded into the system controller. 
     GENERAL IMPLEMENTATION CONSIDERATIONS 
     To actually implement the approach described in the system overview, there are other issues which must be considered before detail design data becomes meaningful. 
     In relation to FIG. 1, it is apparent that the processor/system controller interface 12 must provide some synchronization mechanism to prevent multiple processors from simultaneously interacting with the system controller 10. In addition there must be provided a communication protocol between processor and system controller and the capability of specifying the type of transition (entry, exit or load) being requested by the individual processor. Provisions must also be made for external I/O and interrupt interfaces. 
     Ideally, the processors used in a general purpose transition machine would not be restricted to a single type. The latter considerations have been incorporated into a single coherent approach by including I/O controllers as processors of a specific type. Procedures are then designated as requiring a processor of a specific type (or type category). Then processors requesting eligible subsystems will only be provided with activities compatible with the type of requesting processor. 
     The designation of an assigned subsystem must be provided to the processor. This could be provided in various ways, but an index to the row in the matrices is all that is absolutely essential. Preferably, read, write and execute authorizations associated with an eligible subsystem are provided to the processor by the system controller rather than being obtained by indexed accesses by the processor to the main memory. This latter approach, however, is also possible. 
     The system status vector update requires a dynamically updated condition status vector (V) returned by the processor upon completion of subsystems. T and F could also be stored in the processor&#39;s main memory along with the access authorizations, but in the preferred implementation they are maintained in the system controller. 
     FIG. 14 shows a block diagram of the preferred embodiment of the data constructs which address the implementation considerations described above and are maintained in the System Controller 10. The registers which comprise the processor/System Controller interface 12 are also shown. The processor/System Controller interface 12 contains all the data and control registers accessible by the processor. The structure and use of these registers are set forth in the following Table II. 
     
                       TABLE II______________________________________Descriptor      Definition______________________________________P/Pa binary semaphore used to prevent     multiple processors from accessing the     processor/system controller interface     registers simultaneously. The P/P sema-     phore is set (using a traditional test     and set capability) when a processor     is accessing the processor/system control-     ler interface registers and it is cleared     when no processor is currently accessing     the interface registers.a binary status indicator used to pre-     vent the processors from accessing     the system controller interface regis-     ters while a system transition is in     progress. When a processor initiates     a system transition, it loads the     appropriate data values in the X,     INDEX, TYPE, and V registers (to be     described) and sets the L discrete     true. This requests execution of the     System Controller which resets the L     discrete false when the required tran-     sition is completed.Xa binary status indication used to     notify the System Controller of the     type of system transition to effect.     The X flag is set true by the processor     when the system transition required is     the result of a subsystem exiting, and     X is set false by the processor for a     subsystem entry transition.TYPEa register used to contain the pro-     cessor type indentification. The System     Controller uses this register to deter-     mine the next eligible subsystem whose     identification is to be loaded into     INDEX. TYPE is loaded by a processor     with its processor category when it re-     quests the next subsystem eligible for     execution. The System Controller then     returns the EXECUTE, READ, WRITE, and     INDEX values associated with the next     eligible subsystem, whose type is of     the same category as the value con-     tained in the TYPE register. (This con-     struct is required if a processor is to     be able to request a specific type of     subsystem.)INDEXa register used to contain the iden-     tification of either the next eligible     subsystem or the subsystem currently     being exited. At the completion of     each system entry transition, the System     Controller loads INDEX with the index of     (the number of the row in the matrices     associated with) the next eliglible sub-     system whose type is of the same cate-     gory as the value contained in the     TYPE register. INDEX is loaded by the     System Controller with a special indi-     cator if no subsystems for the current     processor type are eligible. When a     subsystem exits, INDEX contains the     associated subsystem identification,     i.e. the number of the row in the con-     trol matrices associated with the     subsystem.EXECUTEprovides the entry point of the sub-     system whose identification is in INDEX.     This register is loaded only by the     System Controller and is read by the     processors.Vprovides the variable update vector     loaded by the processors upon comple-     tion of a subsystem. This vector     allows a subsystem to return variable     data conditions to the system status     vector.READprovides the pointer(s) to the global     data item(s) accessible to the asso-     ciated subsystem in a read capacity.     READ is loaded by the System Controller     during an entry transition and is un-     used during an exit transition.WRITEprovides the pointer(s) to the global     data item(s) accessible to the associated     subsystem in a write capacity. WRITE     is loaded by the System Controller dur-     ing an entry transition and is unused     during an exit transition.______________________________________ 
    
     It should be noted that in the detail design of the multiprocessor embodiment, an implementation is set forth wherein a multiport controller is used to prevent simultaneous access to the System Controller. In this case, the processors are not required to perform synchronization functions as these functions are performed by the multiport controller. The requirement of a binary semaphore is therefore removed from the processors in this detailed design. 
     It is further noted that the A vector conveniently takes the form of an A matrix for the specific implementation shown in FIG. 14 and defined in Appendix C. 
     System Controller Functional Operation--General Description 
     A functional description of the interaction of the System Controller 10, the interface 12 and processors 2 is now set forth in reference to FIGS. 14-16. 
     The processor capabilities are limited to: 
     (1) requesting the System Controller to provide a subsystem to be executed; 
     (2) executing the subsystem, 
     (3) notifying the System Controller that the subsystem has been completed, 
     (4) updating variable data condition status indications for which the processor is authorized, and 
     (5) loading the System Controller data arrays. 
     Furthermore, all inter-subsystem communication is controlled by the System Controller. 
     When a processor is in an idle state requesting an activity, it performs a test-and-set operation on the P/P semaphore. This semaphore is used to synchronize the processors so that only one processor is accessing the system controller registers contemporaneously. After gaining access to the System Controller it waits until the logic segment of the System Controller is not busy. At that time it stores its processor type identification into the register, TYPE. The register X is set false to indicate a subsystem entry is being requested. The L discrete is set true to signal the System Controller logic to initiate a transition. The processor will then wait until the System Controller logic has completed its operation (indicated by the L discrete being reset). 
     When the System Controller detects that a transition is to be initiated (by the L discrete having been set true), it will determine whether the entry or exit transition has been specified. If the entry transition is specified (indicated by X=false), the matrix logical dot product if performed to obtain the next eligible subsystem of a type compatible with the processor TYPE register. If such an eligible subsystem is determined, its index is stored in the INDEX register, the subsystem access pointer is stored in the register EXECUTE, and the data access pointers are stored in READ and WRITE registers. The active protection specification for the subsystem (the A vector) is used to update the system status vector to preclude inappropriate simultaneous execution of the same subsystem by another processor. (If no eligible subsystem exists for the processor, this will be indicated by returning a null INDEX register.) Then access authorization is returned to the processor by resetting the L discrete false. 
     When the processor detects that transition authorization has been given (by L discrete being reset false and INDEX register containing a non-null value), the following sequence is performed: the INDEX register value is saved, the READ and WRITE registers are obtained to set up the data access linkages, and the EXECUTE register is obtained to set up control linkages. The P/P semaphore is reset to allow other processors access to the System Controller interface registers. Control is passed to the specified subsystem. The subsystem may, in addition to whatever data processing activities are appropriate to it, modify a V register in the processor. 
     When a subsystem exits, the processor performs a test-and-set operation on the P/P semaphore. After gaining access to the System Controller it waits until the logic segment of the System Controller is not busy. At that time the exiting subsystem&#39;s identification is loaded into the INDEX register, the processor copies its own V register into the V register of the System Controller interface, and sets the register X true to indicate a subsystem is being exited. The processor will then activate the System Controller logic by setting the L discrete register true, set itself into an entry request mode, and finally reset the P/P semaphore to allow other processors access to the system controller interface registers. 
     When the System Controller detects that a transition is to be initiated (by the L register having been set true), it determines whether the entry or exit transition has been specified. If the exit transition is specified, the value in the INDEX register is used to index into the data constructs, providing the A, T and F values to incorporate the change in the system status vector caused by the exited subsystem. The V register is also accessed to perform this update. When the status update is complete the System Controller indicates its readiness to honor further requests by resetting the L discrete false. 
     It is to be noted that the TYPE register may be used to identify the various types of processors requesting access to the System Controller so that a subsystem i will not be eligible for execution by the requesting processor unless the processor is of the proper type for carrying out the i th  subsystem. In this manner special processors can be incorporated which are endowed with unique capabilities e.g., floating point processors, vector instruction set processors, byte or word oriented processors, I/O processors, or specific model processors as desired. 
     Interrupts 
     As in most current computing systems, an interrupt facility may be incorporated into the transition machine. One approach to incorporating interrupts is to allocate one row in the System Controller&#39;s data constructs to a null task, which has an R vector of all zeros (i.e., the row will never become eligible on the basis of internal conditions), and T anf F vectors that mask out all non-interrupt bits of the V register update. In other words, all the interrupt related elements of the S vector may be set variably by the interrupt procedure. When the interrupt occurs, the processor will first save the current processor state (program counter, processor status word, etc.) so on completion of the interrupt handling, the processor can return to the previous task. After saving the processor state it will then wait until the logic segment of the System Controller is not busy (indicated by the L discrete being set false). At that time the interrupt procedure in the processor will save the current values of the INDEX and V register and overstore the INDEX register with the index of the System Controller interrupt data constructs row. The interrupt procedure in the processor will then load values associated with the specific interrupt that has occurred into the V register, and initiate an exit transition by setting the System Controller exit mode (i.e., X=true, I=false, and L=true). The interrupt procedure in the processor will then wait until the exit transition has been completed by the System Controller (indicated by the L discrete being reset), will restore the INDEX and V registers with the previously saved values, restore the previous processor state (program counter, etc.) and will return to the interrupted activity. This entire sequence is completely transparent to the interrupted program. The utilization of short execution time subsystems will generally allow adequate time for interrupt processing. A flow diagram of the interrupt handling is shown in FIG. 17. 
     The implementation of interrupts described above is analogous to conventional approaches, and even uses the conventional interrupt interface of conventional processors to accommodate stacking, prioritization, etc. A more direct method is to tie the interrupt lines directly to the System Controller. A unique condition in the system status register S is then allocated to the interrupt. A preempting interrupt generated by the processor/system controller interface is then used to push the processors current state onto a stack and allow subsystems of lesser index (higher priority) to commandeer control of processors involved in lower priority subsystem execution. 
     DETAIL IMPLEMENTATION 
     FIG. 18 illustrates the overall design of a specific implementation of the System Controller 10 and interface 12 of the transition machine 1 in accordance with the invention. The System Controller 10 is seen to comprise a synchronization and control logic circuit 14, a data constructs section 16 (similar to that of FIG. 14), a procedure eligibility determination logic circuit 18 and a system status update logic circuit 20. FIG. 18 also shows the interconnection of each of these major circuit blocks with each other and with the processor/System Controller interface 12. 
     The organization and operation of the logic required to load the System Controller memory (data constructs section) effects the design and operation of the rest of the System Controller. There are many alternate ways the load function may be incorporated in the System Controller design, for instance, non-volatile memory (ROM, PROM, etc.) could be used in the data constructs section which would then have to be loaded while not physically connected to the System Controller, or DMA capabilities could be designed into the System Controller to allow the System Controller to load its memory from the multiprocessor main memory. In view of the different design alternatives, the specific implementation set forth herein is given by way of example and not by way of limitations. 
     The organization and operation of the logic required to generate the &#34;dot&#34; product of the R matrix and the S vector has a significant effect on the design and operation of the System Controller 10. There are many alternate ways the &#34;dot&#34; product may be generated, for instance, each element of the R matrix could be stored in a separate memory register. Each of these registers could be accessed in parallel so with sufficient combinational logic, each element of the eligibility vector could be computed in parallel. This implementation would require a large number of hardware components but would result in a very high speed System Controller. Another alternate implementation would be to use content addressable memories (associative memories) in which to store the R matrix and the TYPE array. Associative memories would allow each component of the eligibility vector to be computed in parallel which would again result in a very high speed System Controller but one which requires a large amount of hardware. Again, in view of the different design alternatives, the specific implementation set forth herein is given by way of example and not by way of limitations. 
     Processor/System Controller Interface 
     As shown in FIG. 18, the processor/System Controller interface 12 consists of a number of data and control registers accessible to both the processor and the System Controller. The structure and use of these registers are set forth in the following Table III. Some of these registers were previously described in the general description and are also included in Table II. The description in Table III gives a more detailed description of their structure and use. 
     
                       TABLE III______________________________________Descriptor    Definition______________________________________STATUSa 4-bit read/write register whose bits are labeled    L, I, X and O, and which contain the following    synchronization, protocol and mode request    information:a binary status indicator used to prevent the    processors from accessing the System Controller    interface registers while a subsystem transition is in    progress. When a processor requests a system    transition, it loads the appropriate data    values in the X, INDEX, TYPE and V registers    and sets the L discrete true. This requests    execution of the System Controller    which resets the L discrete (sets it false) when    the required transition is completed.Ia binary status indicator used to indicate to the    System Controller whether a normal or load    transition is being requested. The I flag is set true    by the processor when the system transition    required is a load transition. The I bit remains true    until the processor resets it upon load completion.Xa binary status indicator used to indicate to the    System Controller whether an entry or exit system    transition is requested. The X flag is set true by    the processor when the system transition required    is the result of a subsystem exiting, and X is set    false by the processor for a subsystem entry    transition. During a load transition X is ignored.Oa binary status indicator set by the System    Controller to notify the processor that no subsystem    is currently eligible. The O bit is set true by the    System Controller when an entry transition results    in no eligible subsystem. The O bit is set false by the System    Controller when an entry transition    results in an eligible subsystem. The O bit is ignored    on exit and load transitions.TYPEa register used to contain the processor type    identification. The System Controller uses this    register to select the next eligible subsystem    appropriate to the requesting processors. TYPE    is fixed for a given processor with its processor    category. During entry transitions the    System Controller returns the EXECUTE,    READ, WRITE, and INDEX values associated    with an eligible subsystem, whose type is of the    same category as the value contained in    the TYPE register. TYPE is ignored during a    subsystem exit transition. During a load transition    TYPE is loaded by the processor with the    processor category required by the subsystem    whose row of data constructs is being loaded    into the System Controller.INDEXa register used to contain the identification of    either the next eligible subsystem, the row currently    being loaded, or the subsystem currently being    exited depending upon the type of transition being    requested. At the completion of each subsystem    entry transition, the System Controller loads    INDEX with the index of the next eligible    subsystem whose type is of the same category as the    value contained in the TYPE register for the    processor. During a load transition,    INDEX is loaded by the processor with the System    Controller row number for the row of constructs    currently being loaded. When a subsystem exit    transition is requested, INDEX will contain the    subsystem identification provided to it by the    System Controller at completion of the entry    transition. Processor interrupts are forwarded to the    System Controller by an exit transition using    an INDEX value dedicated in the System    Controller for that purpose.EXECUTEa register used to provide the entry point of the    subsystem whose identification is in INDEX. This    register is loaded by the System Controller and is    read by the processors during subsystem    entry transitions. EXECUTE is loaded by the    processor and read by the System Controller    during a load transition. During    exit transitions EXECUTE is unused.READa register used to provide the pointer(s) to the    global data item(s) accessible to the associated    subsystem in a read capacity. READ is loaded by    the System Controller during an entry transition    and is loaded by the processor during a load tran-    sition. READ is unused during an exit transition.WRITEa register which provides the pointer(s) to the    global data item(s) accessible to the associated    subsystem in a write capacity. WRITE is loaded    by the System Controller during an    entry transition and is loaded by the processor    during a load transition. WRITE is    unused during an exit transition.Va register used to provide the variable update    vector loaded by the processors upon completion    of a subsystem. This vector allows a subsystem to    return variable data conditions to the system status    vector. (For the specific implementation described    in the appendices, this allows the subsystem    to modify only selected data elements of the S    vector since any attempt to modify unauthorized    elements will be masked out by the T and F    vectors, stored internally to the System    Controller.) During a load transition V is    loaded by the processor with the new S vector    to be loaded in the S register. V is    unused during an entry transition.Ra register which provides a method for the    processor to load the R matrix of the System    Controller. During load transitions the R    register contains the vector to be loaded in    the row of the System Controller&#39;s R matrix    specified by INDEX. The R register is unused    during entry and exit transitions.Aa register which provides a method for the    processor to load the System Controller A    matrix. During load transition the A register    contains the vector to be loaded in the row of    the System Controller&#39;s A matrix specified by    INDEX. The A register is unused during    entry and exit transitions.Ta register used to provide a method for the    processor to load the System Controller T    matrix. During load transitions the T register    contains the vector to be loaded in the    row of the System Controller&#39;s T matrix specified    by INDEX. The T register is unused    during entry and exit transitions.Fa register which provides a method for the    processor to load the System Controller&#39;s F    matrix. During load transitions the F register    contains the vector to be loaded in the    row of the System Controller&#39;s F matrix    specified by INDEX. The F register is unused    during entry and exit transitions.______________________________________ 
    
     For each System Controller there is one set of interface data and control registers as described above. To insure proper operation of the System Controller, no processor may modify these registers while the System Controller is active (i.e., if the L bit in the STATUS register is true). The processors also must be synchronized so that only one processor modifies these registers at a time. This can be accommodated in various ways, for example, a binary semaphore can be employed to avoid the critical section problem and synchronize the processors (as described in the General Implementation Considerations). Alternatively, a multiport organization can be employed where each processor has a dedicated set of interface registers and a multiport controller resolves multiple processor access contention. The multiport controller performs the actual data transfer between the dedicated processor interface registers and the actual system controller registers (similar to the operation of a multiport memory controller). Because of this the processor interface procedures do not require synchronization precautions. The multiport controller implementation therefore accommodates a simpler interface description, and is utilized in the following description. 
     A multiport controller 26 is utilized for the processor/system controller interface 12, as shown in FIG. 19. Each processor 2 has a dedicated set of interface registers 24. The multiport controller 26 selects and synchronizes the actual data transfer between the System Controller 10 and the dedicated processor interface registers 24. An operational logic flowchart of the multiport controller 26 is shown in FIG. 20. The actual interface implementation is transparent to both the processor and the System Controller, so functionally the processor and System Controller are interfaced directly to each other without the requirement for a P/P semaphore. 
     System Controller Functional Operation Detailed Description 
     There are basically three types of allowed processor/System Controller interactions, namely entry, exit, and load transitions. For each type of interaction specific processor actions and System Controller responses are described below: 
     Entry Transition 
     When a processor is in an idle state requesting an activity, it will first wait until the logic segment of the System Controller is not busy which is indicated by the L bit in the STATUS register being set false. At that time it will store its processor type identification into the register, TYPE (if not previously initialized). The X bit in the STATUS register will be set false to indicate a procedure entry is being requested and the L discrete in the STATUS register will be set true to signal the System Controller to initiate a transition. The processor will then wait until the System Controller has completed its operation which is indicated by the L discrete in the STATUS register being reset false by the System Controller. 
     When the System Controller detects that a transition is to be initiated (by the L bit in the STATUS register having been set), it will determine whether the entry, exit, or load transition has been specified. If the entry transition is specified, the matrix dot product is performed with the S vector and the R matrix to obtain the next eligible procedure of a type compatible with the processor TYPE register. If such an eligible procedure is determined, its index is stored in the INDEX register, the procedure access pointer is stored in the register EXECUTE, and the data access pointer is stored in the registers READ and WRITE. The active protection specification for the procedure (the A vector) is used to update the system status vector to preclude inappropriate simultaneous execution of the same procedure in another processor. If no eligible procedure exists for the processor, the System Controller will set the 0 bit in the STATUS register true. In this case the system status vector remains unchanged. Access authorization to the interface registers is returned to the processor by resetting the L discrete in the STATUS register. 
     When the processor detects that access authorization has been given by the L bit of the STATUS register being set false, it first checks to see if any procedures are eligible. This is accomplished by examining the 0 bit in the status register. If the 0 bit is true, indicating no procedures are currently eligible, the processor puts itself into procedure entry mode and reinitiates the entry sequence. If the 0 bit is false, indicating a procedure is eligible the READ and WRITE registers are obtained to set up the data access linkages, and the EXECUTE register is obtained to set up control linkages. Control is passed to the specified procedure using the EXECUTE register value. The procedure may (in addition to whatever data processing activities are appropriate to it) computer a V register value. 
     Exit Transition 
     When a procedure exits, the processor will copy its V register value into the V register of the System Controller, and set the exit discrete, X in the STATUS register true to indicate a procedure is being exited. The processor will then activate the System Controller by setting the L discrete in the STATUS register true, and set itself into an entry request mode. 
     When the System Controller detects that a transition is to be initiated (by the L discrete in the STATUS register having been set), it will determine whether the entry, exit, or load transition has been specified. If the exit transition is specified, the value in the INDEX register is used to index into the data constructs, providing the data to incorporate the change in the system status vector caused by the exit procedure. The V register is accessed to perform this update. Then the System Controller indicates its readiness to honor further requests by resetting the L discrete in the STATUS register. 
     Load Transition 
     When a load transition is initiated under software control, the processor will first wait until the logic segment of the System Controller is not busy (indicated by the L discrete in STATUS being set false). At that time the processor will store in the INDEX register the number of the row in the System Controller matrices which is to be loaded. The data to be loaded into each of the EXECUTE, READ, WRITE, TYPE, R, T, F, and A matices will be placed into the corresponding interface registers and the initial S vector will be placed in the V register. The load procedure is essentially an application program that transfers the System Controller data constructs from processor main memory to the System Controller. The processor sets the I discrete in the STATUS register true to indicate a load transition is being initiated and then activates the System Controller logic by setting the L discrete true in the STATUS register. The processor then resets itself into any one of the transition modes, entry, exit, or load depending on which transition is required. (It should be noted that the load procedure assumes there are no entry or exit transitions being performed for other processors. This can be guaranteed by assuming a load procedure is entered as the last eligible activity in the data constructs, when all processors are idle. Initializing S=0 will guarantee this status until load complete, at which time the initial S vector is passed). 
     FIG. 21 represents a processor operational flowchart for each of the entry and exit transitions, and FIG. 22 is the processor operational flowchart for a load transition. FIG. 23 represents the System Controller operational flowchart including the entry, exit, and load transitions. 
     SYSTEM CONTROLLER DETAILED COMPONENT DESIGN 
     As shown in FIG. 18, the System Controller 10 is comprised of a synchronization and control logic circuit 14, a data constructs section 16, a procedure eligibility determination logic circuit 18, and a system status update logic circuit 20. A specific detailed design for each of these four components is described below: 
     Data Constructs 
     As shown in FIG. 24, the data constructs section 16 of the System Controller 10 contains the System Controller memory. The memory may comprise eight random access memory modules, one for each of the R, A, F, T, TYPE, EXECUTE, READ, and WRITE arrays. Each of these arrays contain the same number of elements and are addressed concurrently. Each element (row) of the R, A, F, and T arrays contain the same number of bits, which is equal to the number in the system status register. Depending on the machine application and the organization of the System Controller memory load logic, these memories can be either read only (ROM, PROM, etc.) or read/write. For purposes of illustration, read/write memories are utilized which are loaded by the processor. In addition to the data arrays described above the data constructs section 16 also contains a read/write register called the S register, in which the system status vector, S, is stored. 
     There are a total of 14 inputs and outputs for the data constructs section 16 each of which is described in the following Table IV. 
     
                                           TABLE IV__________________________________________________________________________    Definition__________________________________________________________________________ADDRESSa multiple bit address bus that is capable of addressing each    element of the R, A, T, F, TYPE, READ, WRITE, and EXECUTE    arrays. The arrays are addressed concurrently, e.g., if ADDRESS    =    2 then the second element of each array is addressed.CEa one bit signal that enables the eight memory modules to be read    or written. When CE is true (i.e., logical 1) the contents of    each    array element indicated by ADDRESS is read (R/--W = &#34;1&#34;) or    written    (R/--W =&#34;0&#34;) to or from the associated data bus. When CE is    false    (i.e., logical &#34;0&#34;) no array can be read or written.R/--Wa one bit signal input to each of the eight memory modules that    specify a read or write action. When R/--W is true (i.e.,    logical &#34;1&#34;)    and CE is true (i.e., logical &#34;1&#34;) the contents of the array    element    indicated by ADDRESS is output on the corresponding data bus.    When R/--W is false (i.e., logical &#34;0&#34;) and CE is true (i.e,    logical &#34;1&#34;)    the contents of each data bus is written into the associated    array    element specified by ADDRESS.S.sub.NEWa multibit data input to the read/write S register. S.sub.NEW contains    the updated status vector returned by the system status update    logic as the result of an entry, exit or load transition.S.sub.LATCHa control signal which, when enabled (transitions from logical &#34;0&#34;    to logical &#34;1&#34;), causes the contents of S.sub.NEW data input to    be    latched into the S register. When S.sub.LATCH is disabled    (logical &#34;0&#34;)    the contents of the S register remain unchanged independent of    changes in S.sub.NEW.R.sub.iT.sub.iF.sub.imultiple bit, bidirectional data buses. Data from each of theA.sub.i  eight memory modules are output to (or input from) the    associatedEXECUTE.sub.i    data buses.READ.sub.iWRITE.sub.iTYPE.sub.ia multiple bit data bus on which the content of the S register is    output.__________________________________________________________________________ 
    
     Procedure Eligibility Determination Logic 
     The procedure eligibility determination logic circuit 18 is contained within the System Controller 10 and contains the combinational logic necessary to determine procedure eligibility during entry transitions. A subsystem is eligible if the type of processor making the request (content of the TYPE interface register) is equivalent to the processor type required by the selected subsystem (content of the TYPE i  data bus) and all data conditions in the S vector relevant to enabling the subsystem are true (i.e., the vector resulting from forming the logical &#34;OR&#34; of the ith row of the R array and the current S vector contains all ones). 
     FIG. 25 is a block diagram of the procedure eligibility determination logic. In reference to FIG. 18 and FIG. 25, line 30 represents a multiple bit data bus which contains the current contents of the TYPE register in the processor/System Controller interface 12. Line 32 is a multiple bit data bus which contains the processor type associated with the subsystem currently indexed, namely, TYPE i . Line 34 represents a multiple bit data bus which contains the R vector associated with the subsystem currently indexed, namely, R i . Line 36 is a multiple bit data bus from the S register of the data constructs section 16 (FIG. 24) which feeds the current contents of the S register to the procedure eligibility determination logic circuit 18. The output of the circuit 18 is a single data bit representative of a single component of the eligibility vector E along output line 38. E is logical &#34;1&#34; when the indexed subsystem is eligible and logical &#34;0&#34; otherwise. The logical expression for E may be written as follows: ##EQU1## Where the symbol θ is used to denote logical equivalence, and ##EQU2## denotes the logical &#34;AND&#34; of each element of the vector operated on, resulting in a single signal that will be true (i.e., logical &#34;1&#34;) if all elements in the vector are true, e.g., ##EQU3## 
     The logic circuitry of FIG. 25 implements the above equation. In reference to FIG. 25 the signal along data bus lines 30 and 32 are fed to a multibit comparator 40 which produces a single output bit along line 42. The output bit is a logical 1 only if the data on the TYPE data bus (line 30) is identical to the data on the data bus (line 32) corresponding to TYPE i  (all bits equivalent), and otherwise the output along line 42 is a logical 0. The data bits along bus lines 34 and 36 are input to an OR gate which is represented in FIG. 25 by a single conventional OR symbol. It is understood, however, that each of the corresponding bits along lines 34 and 36 are separately OR&#39;ed similar to the circuit shown in FIG. 26. The line running trasverse of the input and output lines of the logical OR thus indicate the multiple OR circuit of FIG. 26. AND circuits are similarly represented in the drawings, e.g., gate 48. The definition utilized in the circuit design is such that S j  =1 if the j.sup. th data condition is true, and R ij  =0 if the j th  data condition is relevant to procedure i. Consequently the OR, AND sequential logic is appropriate. Thus, in reference to FIG. 25, the multiline output of OR gate 46 is fed to a corresponding multiple input AND gate 48 which provides a single output along line 50 to AND gate 52. A second input of AND gate 50 is derived from the output of comparator 40 along line 42. 
     System Status Update Logic Circuit 
     The system status update logic circuit 20 contains the combinational logic required to perform updates to the system status vector, S, appropriate to the transition being initiated. During an entry transition, the logical expression for the S NEW  vector generated is: 
     
         S.sub.NEW =S.sub.OLD  A.sub.i 
    
     During an exit transition, the logical expression for the S NEW  vector generated is: 
     
         S.sub.NEW =(S.sub.OLD  T.sub.i) (A.sub.i  T.sub.i) (T.sub.i  F.sub.i) (V F.sub.i) 
    
     This expression is summarized by Table B.2 given in Appendix B. During the load transition, the logical expression for S NEW  is: 
     
         S.sub.NEW =V 
    
     FIG. 27 is a block diagram of the system status update logic circuit 20. As shown in FIG. 27, the system status update logic circuit 20 comprises a plurality of OR and AND logic circuits (see FIG. 26 for example) identified by numbers 60, 62, 64, 66, 68 and 70. AND gates 64, 66, and 68 have one group of inverting input terminals and one group of non-inverting input terminals. Element 70 is a multiple input/output OR gate (see FIG. 26) wherein each input/output line is a multiple bit data bus. The output of OR gate 70 is fed to an input terminal of a 3-to-1 multiplexer 72 along lines 74. A second group of inputs to multiplexer 72 is fed in along lines 76 from the output of AND gate 60. A third input is fed to multiplexer 72 along lines 78. The output of multiplexer 72 is a data bus 80 representative of the new status vector S NEW  and is fed to the S register of the data constructs section 16 (see FIGS. 18 and 24). 
     The input lines (generally data buses) to update circuit 20 are fed in along lines 82, 84, 86, 88, 90, 92 and 94. Line 82 carries the single bit I discrete value from the system STATUS register of the interface 12. Line 84 carries the single X bit from the STATUS register. The two signals determine the select code at terminals SELI, SEL2 of the multiplexer 72. If I is true (SELI=1) a load transition is indicated (regardless of X) and multiplexer 72 passes the current V vector from lines 94 and 78 to the output data bus 80. If I is false (SELI=0) the S NEW  output is determined by the value of the X bit of the STATUS register. If X is true, S NEW  is shown by the logical expression set forth above. This logical equation is associated with an exit procedure and is achieved using the condition code 01 for SELI, SEL2=01. Associated logic circuits include input lines 86, 88, 90, 92 and 94, AND gates 60, 62, 64, 66, 68, and OR gate 70. 
     When both X and I are false, SELI, SEL2=0,0, the new status vector is simply given by S OLD   A i  and corresponds to any entry transition using AND gate 60 and lines 76. 
     Synchronization and Control Logic Circuit 
     The synchronization and control logic circuit 14 contains the clocked sequential logic required to control the operation and internal connections of all the components of the System Controller. The various input and output lines associated with the logic circuit 14 are generally shown in FIGS. 18 and 28 with a detailed schematic diagram illustrated in FIG. 29. The function of the L, I, and X bits of the STATUS register and the INDEX register of the interface 12 have been set forth above (see Table III for example). Similarly, ADDRESS, CE, R/W and S LATCH  have already been defined (see, for example, Table IV). These latter signals are all generated by the synchronization and control logic circuit 14 and fed primarily to the data constructs section 16. The ADDRESS bus is also latched into the INDEX register of the interface 12 during entry transitions when an eligible subsystem is detected. Additional signals outputted by the synchronization and control logic circuit 14 are set forth in the following Table V. 
     
                       TABLE V______________________________________Descriptor Definition______________________________________ENTRY LATCHa one bit control signal output by the      synchronization and control logic to the      processor interface registers. This      signal causes the current values of the      EXECUTE, READ, WRITE and the      ADDRESS data buses to be latched into the      EXECUTE, READ, WRITE and INDEX      register in the processor interface 12. This      signal is enabled only during entry transitions      when an eligible subsystem is detected.L RESETa one bit control signal output by the      synchronization and control logic to the      processor interface registers. When      enabled, this signal causes the L discrete of      the processor interface STATUS register to      be set false (i.e., logical &#34;0&#34;). The      synchronization and control logic enables      this signal at the completion of      each transition.a one bit data signal input to the      synchronization and control logic from      the procedure eligibility determination      logic. This signal represents the eligibility      (E = &#34;1&#34;) or noneligibility (E = 0) of the      subsystem currently indexed. The E signal is      used by the synchronization and control      logic during entry transitions to      detect an eligible subsystem.Oa one bit data signal output by the      synchronization and control logic to the      processor interface registers. the 0      signal is set true (i.e., logical &#34;1&#34;) if during      an entry transition no eligible subsystem      is detected, otherwise 0 signal is always false.      When the L reset signal is enabled at the      completion of each transition, the content of      the 0 bit is latched into 0 discrete in      the processor STATUS register.______________________________________ 
    
     A specific implementation of the synchronization and control logic is shown in FIG. 29. Other logic combinational arrangements are possible with the design criteria simply being to reproduce the various outputs of FIG. 28 with the various possible combinations of the input variables L, I, X, E and INDEX. The state diagram is shown in FIG. 30 which follows from the flowchart of FIG. 23. In FIG. 30, the symbol φ indicates a &#34;don&#39;t care&#34; condition. The design of the logic circuit from the state diagram may be done in accordance with well known techniques as set forth, for example, by M. M Mano, Computer Logic Design, Prentice-Hall, Inc. (1972), pp 200-236. The state assignments utilized in the logic design are as follows: 
     
         ______________________________________J-K                     J-KFlip Flop               Flip FlopState120    122    124  126  State                             120  122  124  126______________________________________A =  0      0      0    0    G =  1    1    0    0B =  0      0      0    1    H =  1    1    0    1C =  0      0      1    0    I =  1    0    1    1D =  0      1      0    0    J =  1    0    0    0E =  1      0      0    1    K =  1    1    1    0F =  1      0      1    0    L =  1    1    1    1______________________________________ 
    
     For implementing the state diagram four JK flip-flops 120, 122, 124 and 126 are used together with a clock generator 128 and loadable counter 130. With regard to the state assignments above, the most significant bit correspond to flip-flop 120, the next most significant bit to flip-flop 122, etc. Counter 130 is loaded by the INDEX register from interface 12. The detail timing diagrams are illustrated in FIGS. 31-34 in reference to the design description set forth below. 
     System Controller Internal Operation 
     The System Controller has three internal modes of operation, one for each of the entry, exit and load transitions. During an entry transition (initiated by the L discrete of the interface STATUS register being set true) the synchronization and control logic circuit 14 begins accessing successive rows (i.e., each successive element of the eight memory modules) of the data construct matrix assays, causing them to be output on their respective data buses. As each element is output, the subsystem eligilibility determination logic circuit 18 computes the eligibility of the associated subsystem, and the system status update logic circuit 20 generates the S NEW  vector based on the current system status vector and the A vector associated with the subsystem indexed. It will be recalled that the A vector is used to preclude inappropriate simultaneous execution of the same subsystem in another processor. If the subsystem is found eligible, the synchronization and control logic circuit 14 causes the S register to latch the S NEW  vector, transfers access and control information (i.e., EXECUTE i , READ i , WRITE i , and ADDRESS) from the associated data buses to the processor interface registers, and returns access authorization to the processor by resetting the L busy discrete in the interface STATUS register. If no subsystem is found eligible the synchronization and control logic circuit 14 notifies the processor by setting the 0 discrete in the interface STATUS register and returns access authorization to the processor. In this instance, no system status vector update occurs. 
     Accessing successive rows of the R matrix and recycling to i=o at each new entry transition (see FIG. 23) enables the computer programmer to establish a priority application program sequence. Thus subsystems of a higher priority are placed earlier in the row sequence. It is noted however that such a sequential accessing is not required, and indeed, even a random accessing technique would be possible. An alternate approach which involves computing the matrix dot product in parallel as opposed to the sequential method described above is also possible. 
     FIG. 31 represents the timing diagram of the control and data signals in the System Controller during an entry transition resulting in an eligible subsystem being detected which is associated with the third row of the data constructs. It is assumed for the purpose of illustration that each memory array of the data constructs contains only four rows. FIG. 32 represents a similar timing diagram for an entry transition where no subsystem is detected as eligible. 
     During an exit transition, the synchronization and control logic circuit 14 accesses one row (i.e., one element from each of the eight memory modules) in the data constructs section 16. The value stored in the INDEX register is used as the address to select the appropriate row. As each element is output on it&#39;s associated data bus, the system status updated logic circuit 20 generates the S NEW  vector from the current S vector, the T, F, and A vectors associated with row indexed, and the V vector returned by the processor in the V register of the interface 12. The synchronization and control logic circuit 14 causes the S register to latch the S NEW  vector and returns access authorization to the processor by resetting the L discrete in the STATUS register. FIG. 33 represents the timing diagram of the control and data signals in the System Controller during an exit transition. 
     During a load transition the synchronization and control logic circuit 14 first causes the content of each of the interface data registers, R, A, T, F, EXECUTE, READ, WRITE, V, and TYPE to be transferred to the associated data buses. Next, a row (i.e., one element from each of the eight memory modules) in the data constructs section 16 is accessed in a write mode. The value stored in the INDEX register of interface 12 is used to select the row accessed. This causes the content of each data bus to be written into the addressed element of the associated memory module. The synchronization and control logic circuit 14 latches the S NEW  vector which is input from the interface 12 V register (see multiplexer in FIG. 27) and returns access authorization to the processor by resetting the L discrete in the STATUS register. FIG. 34 represents the timing diagram of the control and data signals in the System Controller during a load transition. 
     SINGLE PROCESSOR TRANSITION MACHINE ARCHITECTURE 
     The transition machine architecture described above may also be applicable in a single processor embodiment. In reference to FIG. 35, a single processor, P, has access to all of memory M which contains all of the application programs and data base items defined as part of the computation system. The System Controller 100 is of the same general construction as that shown in FIG. 14, and may generally be thought of as comprising a synchronization and control logic circuit 14&#39;, a data constructs section 16&#39;, a procedure eligibility determination logic circuit 18&#39;, and a system status update logic circuit 20&#39;. 
     The data constructs section contains all of the fixed preamble information concerning the subsystems and data base as well as dynamic systems status information. As before, row i in the R, T and F matrices and in the EXECUTE, READ and WRITE arrays, are all associated with subsystem i. EXECUTE is an array of starting addresses for the subsystem, and READ and WRITE are arrays of pointers to data pointer packets associated with the data access requirements of subsystem i. Each column in the matrices R, T and F, and the vectors S and V, is associated with a data condition, j. The j th  column is associated with the same condition in all cases. The A matrix and TYPE vector of FIG. 14 are not present as these constructs apply only to multiprocessor configurations. The detail implementation of the various components 14&#39;, 16&#39;, 18&#39; and 20&#39; is thus modified in a straightforward manner from the embodiments shown in FIGS. 24, 25, 27 and 29 to remove the A and TYPE constructs. Further, the processor/system controller interface may be comprised from registers within the uniprocessor P which are dedicated to perform the various functions discussed heretofore, for example, in relation to FIGS. 14-18 and Table III. These registers are accessible by both the processor P and System Controller 100. In net effect, a separate interface hardware apparatus may not be required. FIG. 35 illustrates the case wherein interface 12&#39; is part of the processor P. 
     Entry Transition 
     When the processor is in an idle state requesting an activity, it will first wait until the logic segment of the system controller is not busy (L discrete set false). At that time it will check to see if any subsystems are eligible. This is accomplished by examining the 0 bit in the STATUS register. If the 0 bit is true (indicating no subsystems are eligible), the system has completed execution. The processor will therefore cycle awaiting an eligible subsystem which can only be enabled as the result of an external interrupt. If the 0 bit is false, indicating a subsystem is currently eligible, the READ and WRITE registers are obtained to set up to the data access linkages, and the EXECUTE register is obtained to set up control linkages. Control is passed to the specified subsystem using the EXECUTE register value. The subsystem may (in addition to whatever data processing activities are appropriate to it) compute a V register value. The entry transition procedures performed by the processor are the same as those performed in the multiprocessor case as shown in FIG. 21. The handling of these actions outside the processors is modified to the extent that the system controller is interfaced directly with the processor rather than with synchronization support provided by the multiport controller. 
     Exit Transition 
     When a subsystem exits, the processor will copy its V register value into the V register of the System Controller, and set the exit discrete, X in the STATUS register true to indicate a procedure is being exited. The processor will then activate the System Controller by setting the L discrete in the STATUS register true, and set itself into an exit request mode. 
     When the System Controller detects that a transition is to be initiated (by the L discrete in the STATUS register having been set), it will determine whether the entry, exit, or load transition has been specified. If the exit transition is specified, the value in the INDEX register is used to index into the data constructs, providing the data to incorporate the change in the system status vector caused by the exiting subsystem. The V register is accessed to perform this update. Then the System Controller indicates its readiness to honor further requests by resetting the L discrete in the STATUS register. These operations of the processor and System Controller are illustrated in FIGS. 21 and 23 respectively. (The TYPE and A constructs in FIG. 23 are not appropriate to this case). 
     Interrupts are handled by the interrupted processor by saving the processor state, loading a special dedicated value into INDEX, and loading a special V register value indicating the interrupt status. An exit transition is then initiated by the processor. When the exit transition completes, the salvaged state of the interrupted processor will be restored. This procedure is shown in FIG. 17. 
     Load Transition 
     When a load transition is initiated under software control, the processor will first wait until the logic segment of the System Controller is not busy (indicated by the L discrete in STATUS being set false). At that time the processor will store in the INDEX register the number of the row in the System Controller matrices which is to be loaded. The data to be loaded into each of the EXECUTE, READ, WRITE, R, T and F matrices will be placed into the corresponding interface registers and the initial S vector will be placed in the V register. The load procedure is essentially an application program that transfers the System Controller data constructs from processor main memory to the System Controller. The processor set the L discrete in the STATUS register true to indicate a load transition is being initiated and then activates the System Controller logic by setting the L discrete true in the STATUS register. The processor then resets itself into any one of the transition modes, entry, exit or load depending on which transition is required. 
     The algorithms for the processor logic and System Controller logic for the single processor embodiment are shown in FIGS. 36A and 36B respectively. A design language with self-explanatory syntax is used for ease of explanation. 
     SELECTED ALTERNATE IMPLEMENTATIONS OF THE SYSTEM CONTROLLER 
     The specific implementation and operation of the System Controller is dependent upon the specific objectives of the computing system. For example, three specific design objectives are: 
     (1) To implement a system controller to effect exploitation of inherent software productivity advantages even in a conventional uniprocessor or multiprocessor computing system. 
     (2) To implement a highly efficient central control mechanism to control a multiprocessor. The design of this device would be dependent on the type of processors being controlled (i.e. mainframes, minicomputers, or microcomputers). 
     (3) To implement a highly efficient central control mechanism for a conventional single processor which effectively reduces operating system overhead. The design of this device would again be dependent on the type of processor used. 
     The advantages associated with the first implementation objective have already been discussed. The advantages associated with the second and third implementation objectives are the result of a very efficient hardware implementation of a function for which an analogous function is typically implemented in software. 
     For some applications, all aspects of the System Controller need not be included. Many advantages of the concept of having a separate central controlling device can be realized with a partial implementation of the device described above. For example, to meet the third objective identified above a system controller device can be defined which includes only a subset of the complete system controller previously described. One version of a limited system controller is described in detail as an example of an alternate design for a controlling device which is based on the same basic concepts but requires only a subset of the system controller components. 
     System Controller to Support a Conventional Operating System 
     Conventional operating systems for major computing systems are typically implemented to process what is called a job control language. Thus, in order to run a job, a programmer imbeds job control statements throughout the programs, which effect calls to the operating system to perform resource or task control related functions. The performance of these functions by the operating system contributes greatly to program execution overhead (on the order of thirty percent), and is a very costly commodity particularly using large-scale mainframe systems. 
     In the alternate implementation described herein, programs which comprises the resource and task management aspects of the operating system are written as transition machine programs. The application programmer generated job control statements remain unchanged as well as the form of the application programs. A specialized System Controller having fewer data constructs is interfaced to or integrated into the architecture of the processor. The primary function to be performed by this special System Controller is to efficiently perform the task dispatch function for the conventional processor. This function is typically performed in software which results in a significant amount of overhead. 
     FIG. 37 represents the overall design of a specific implementation of the single processor System Controller 210. This version of the System Controller is seen to comprise a synchronization and control logic circuit 214, a data constructs section 216, and a procedure eligibility determination logic circuit 218. The data constructs section 216 herein contains only the R matrix and is thus a simplified version of the data constructs section 16 shown in FIG. 24. Similarly, the synchronization and control logic circuit 214 and the procedure eligibility determination logic circuit 218 are simplified versions of their counterpart circuits shown in FIGS. 25 and 29 respectively inasmuch as only the input and outputs shown in FIG. 37 need be utilized. FIG. 37 also shows the interconnection of each of these major circuit blocks with each other and with a plurality of processor/System Controller registers 212. These registers may be general purpose registers of the processor which is shown as a conventional computer 220. The conventional computer 220 is seen to comprise an operating system 222 which provides control for execution of the various subsystems and for a load logic section 224 and S vector update logic 226. The S vector update logic is thus performed as parts of a software executive routine. It is also to be noted that this embodiment of the invention does not require a complete program separation between data transformation and program control as suggested in the example program set forth above. Even with direct transfer of control (branching, etc) in the application programs, the hardware executive apparatus of the System Controller is effective for reducing the software executive overhead which would otherwise be required. 
     The structure and use of these processor/system controller registers 212 are similar to the interface registers set forth heretofore and are summarized in the following Table VI. 
     
                       TABLE VI______________________________________Descriptor  Definition______________________________________STATUSa two bit read/write register whose      bits are labeled L and I and which      contains the following information:a binary status indicator used to      prevent the processors form accessing      the processor/system controller re-      gisters while a system transition is      in progress. When a processor re-      quests a system transition, it loads      the appropriate data values in the      INDEX, R and S registers and sets the      L discrete true. This requests exe-      cution of the System Controller which      resets the L discrete (sets it false)      when the required transition is com-      pleted.Ia binary status indicator used to      indicate to the System Controller      whether a normal or load transition      is being requested. The I flag is set      true by the processor when the system      transition required is a load transi-      tion. The I bit remains true until      the processor resets it upon load com-      pletion.Ra register which provides a method      for the processor to load the R matrix      of the System Controller. During load      transitions the R register contains      the vector to be loaded in the row of      the System Controller&#39;s R matrix spe-      cified by INDEX. The R register is      unused during entry and exit transi-      tions.INDEXDuring a load transition, INDEX is      loaded by the processor with the Sys-      tem Controller row number of the row      of the R matrix currently being loaded.      INDEX is not used during entry transi-      tions.Sa register which contains the current      system status vector. This register is      updated by the processor on completion      of each subsystem to effect changes to      the global status indications that      occurred during execution of the sub-      system. The content of the S register      is used by the System Controller during      each subsystem entry transition in      combination with the R matrix to gen-      erate the new procedure eligibility      vector E.Ea shift register which contains a      vector indicating the eligibility      status of every defined subsystem in      the system. The E vector is generated      one bit at a time by the procedure      eligibility determination logic. As      each bit is generated, the synchroniza-      tion and control logic causes the E      register to be shifted one position      (by the SHIFT E control signal) which      latches in the eligibility indicator      of the current subsystem. The E      register is not used during load      transitions.______________________________________ 
    
     Functional Operation 
     There are basically two types of allowed processor/System Controller interactions, namely the entry and the load transitions. For each type of interaction, the specific processor actions and the System Controller responses are described below. 
     Entry Transition 
     When a processor is in an idle state requesting an activity, it will first wait until the logic segment of the System Controller is not busy which is indicated by the L bit in the STATUS register being set false. At that time, the I bit in the STATUS register will be set false to indicate a procedure entry is being requested and the L discrete in the STATUS register will be set true to signal the System Controller to initiate a transition. The processor will then wait until the System Controller has completed its operation which is indicated by the L discrete in the STATUS register being reset false by the System Controller. (This procedure may be implemented as a macro instruction whose execution time matches the system controller delay.) 
     When the System Controller detects that a transition is to be initiated (by the L bit in the STATUS register having been set), it will determine whether an entry or load transition has been specified. If the entry transition is specified, the matrix dot product is performed with the S vector and the R matrix to obtain the new eligibility vector which is stored in the E register. Access authorization to the registers 212 is returned to the processor by resetting the L discrete in the STATUS register. 
     When the processor detects that access authorization has been given (by the L bit of the STATUS register being set false), it first checks to see if any subsystems are eligible. This is accomplished by examining the E vector contained in the E register. If the entire E vector is zero, indicating no subsystems are currently eligible, the system is either blocked until an external interrupt frees up resources or the associated job has completed. In the latter case the processor must initiate a System Controller load transition to bring in the next job to execute. If the E register is non-zero, the bit position index of the first non-zero entry in the E vector is used to obtain the task control information associated with the eligible subsystem. This bit in the E vector is then reset. Control is then passed to the specified subsystem. The subsystem may (in addition to whatever data processing activities are appropriate to it) modify the S register in a sense analogous to the update requirements discussed previously. On completion of the subsystem the processor examines the E register again to determine the next eligible subsystem. This cycle continues until all the eligible subsystems have been executed and the corresponding bits in the E register have been reset. At this time the processor activates the System Controller to perform another entry transition. 
     Load Transition 
     When a load transition is initiated under software control, the processor will first wait until the logic segment of the System Controller is not busy (indicated by the L discrete in STATUS being set false). At that time the processor will load in the INDEX register the number of the row in the System Controller R matrix which is to be loaded. The data to be loaded into the indexed row of the R matrix will be placed into the R interface register. The load procedure is essentially an application program that transfers the System Controller data constructs from processor main memory to the System Controller. The processor sets the I discrete in the STATUS register true to indicate a load transition is being initiated and then activiates the System Controller logic by setting the L discrete true in the STATUS register. The processor then resets itself into the appropriate transition modes, entry or load. 
     FIG. 38 represents a processor operational flowchart for the entry transitions, and FIG. 39 is the processor operational flowchart for a load transition. FIG. 40 represents the System Controller operational flowchart including the entry and load transitions. 
     While the invention has been described in terms of preferred embodiments, it is clear that modifications and improvements may be made by those skilled in the art, and it is intended that the invention include all such modifications and improvements which fall within the spirit and scope of the invention. 
     APPENDIX A 
     In the implementation of the model of parallel computation, specific definitions are assigned to the set of constructs R, S and E and the matrix algebraic operation, &#34;·&#34; on these constructs with effect a transition system. 
     Definition A.1. The system status vector, S is a set of binary status indications on the data set d such that for every data condition there is an associated status indications, S j  in S if and only if S j  is relevant to enabling some procedure in the system. S j  =1 if the associated data condition is met, S j  =0 otherwise. 
     Definition A.2. The system eligibility vector, E is a set of binary status indications on the set of unary predicates, R i , indicating whether R i  is currently satisfied, enabling the associated procedure. E i  =1 indicates the associated unary predicates are satisfied; E i  =0 otherwise. 
     Definition A.3. A system status condition, S j  is relevant to enabling procedure i if and only if the data condition whose status is indicated by S j  is included in the unary predicates, R i . 
     Proposition A.1. The unary predicates, R i  can be represented as a set of binary relevance indications associated (and in conjunction) with each of the conditions whose status is maintained in S. This proposition follows directly from the previous definitions. 
     Definition A.4. The relevance matrix, R is comprised of binary relevance indications, r ij  indicating the relevance of system status condition j to enabling procedure i. Relevance is indicated by r ij  =0, irrelevance by r ij  =1. 
     Definition A.5. The logical dot product, P of a matrix M times a vector, V with compatible dimensions is defined as the vector, P=M·V, where ##EQU4## 
     Proposition A.2. The system eligibility vector, E can be computed appropriate to a given state of the system by taking the logical dot product of the relevance matrix R and the system status vector, S. 
     Proof: From Definition A.5 it follows that: ##EQU5## 
     From Definitions A.4 and A.1 it follows that r ij  v s j  =1 if and only if the condition j is either met or irrelevant to enabling procedure i. Then by proposition A.1 is follows that [R·S] i  =1 if and only if all conditions of the unary predicates R i  are satisfied. Thus, [R·S] i  =E i  by Definition A.2, and it is proved that E=R·S as proposed. 
     APPENDIX B 
     Specific definitions are assigned to the constructs T, F, V and their functional relationship. The definitions which follow are used to restrict access of application programs. 
     Definition B.1. The j th  element, t ij  of the true condition vector, T i  is a binary status indication associated with the procedure i and the system status condition, j such that t ij  =1 implies condition j is either satisfied or unchanged by the completion of procedure i. 
     Definition B.2. The j th  element, f ij  of the false condition vector, F i  is a binary status indication associated with the procedure i and the system status condition, j. The element f ij  =1 implies the condition j is either not satisfied or unchanged by the completion of procedure i. 
     Definition B.3. The variable condition update vector, V is a set of binary status indications which can be set dynamically by the procedure running in a sequential processor. The component V j  is set to 1 by the procedure to indicate that system status condition j is satisfied or V j  is set to 0 to indicate condition j is not satisfied. 
     Proposition B.1. The four possible implications on change in system following completion of procedure i can be computed according to the formula: 
     
         S=(S T.sub.i) (F.sub.i  V.sub.i) (T.sub.i  F.sub.i) 
    
     where the bar indicates the logical NOT operation. 
     Proof: The proof follows directly from the definitions of the associated vectors as shown in the Truth Table B.1 given below. 
     It should be noted that there are many forms which proposition B.1 could take. The expression used has the advantage of restricting the range of V i  such that procedure i can only modify conditions for which it is authorized. 
     Proposition B.2. The range of V is restricted such that V modifies only a specified subset of the system status conditions, j. This subset is determined by T i  and F i  for procedure i such that S j  is determined by V j  if and only if t ij  =0. 
     Proof: The implied new values of S j  for the various values of t ij  and f ij  from proposition B.1 are shown in Table B.2 taken from Table B.1 from which the proposition follows directly. 
     
                       TABLE B.1______________________________________ SYSTEM STATUS CONDITION TRANSITIONTRUTH TABLES.sub.jOLD  f.sub.ij         t.sub.ij                V.sub.j                     S.sub.jNEW                             EXPLANATION______________________________________0      0      0      0    0       S set variably false0      0      0      1    1       S set variably true0      0      1      0    1       S set true fixed0      0      1      1    1       S set true fixed0      1      0      0    0       S set false fixed0      1      0      1    0       S set false fixed0      1      1      0    0       S unchanged0      1      1      1    0       S unchanged1      0      0      0    0       S set variably false1      0      0      1    1       S set variably true1      0      1      0    1       S set true fixed1      0      1      1    1       S set true fixed1      1      0      0    0       S set false fixed1      1      0      1    0       S set false fixed1      1      1      0    1       S unchanged1      1      1      1    1       S unchanged______________________________________ 
    
     
                       TABLE B.2______________________________________RESTRICTIONS ON THE RANGE OF Vt.sub.ij f.sub.ij S.sub.jNEW                    Implications to System Status______________________________________1     1        S.sub.jOLD                    unchanged1     0        1         set true0     1        0         set false0     0        V.sub.j   set variably______________________________________ 
    
     APPENDIX C 
     In order to accommodate exclusive data access as well as prohibiting simultaneous activation of the same procedure in more than one processor, the single activation vector is extended so as to negate availability of data which is to be updated by a procedure. This will accommodate the equivalent of a single step function very useful in checkout phases in parallel programs. This can be done by defining a matrix whose row vectors are associated with procedures. Each A i  is defined as a logical subset of the row in R associated with i. And so its definition follows from the definition of R (Appendix A) for any particular implementation. 
     Definition C.1. The vector A i  is a set of binary status conditions A ij , where the index j is associated with the conditions whose status is maintained in S. A ij  =1 if and only if the j th  condition is a mutually exclusive data availability condition required at entry to procedure i; A ij  =0 otherwise. If A i  equals the i th  row in R identically, then all such procedures with any entry conditions in common must execute sequentially. 
     Proposition C.1. Modifying the system status vector according to the formal S=S A i  prior to entry is sufficient to effect access protection for procedure i. 
     The proof of this proposition follows immediately from Definitions C.1, A.1, and A.4. 
     Proposition C.2. Modifying the system status vector according to the formula S=S A i  restores S to its original value. 
     Proof: The proof of this proposition follows directly from Definition C.1 and Proposition C.1 if there are no changes to S between entry and exit of the i th  procedure. When there are other procedures initiated or terminated in the interval, the proof holds because no procedures can proceed in parallel if they are affected by or affect the same data availability condition covered by A i . And therefore, for every condition for which A ij  ≠0 there will have been no intermediate change to S and the proof is completed. 
     Proposition C.3. The change in system status following completion of procedure i can be computed according to the formula: 
     
         S=[(S A.sub.i) T.sub.i)] (F.sub.i  V.sub.i) (T.sub.i  F.sub.i) 
    
     The proof follows directly from the proofs of propositions B.1 and C.2.