Abstract:
A method and associated systems for handling a service request in a hybrid computer system. The hybrid computer system includes an application server computer and at least two mainframe computers. The server computer receives a service request from a user application, determines that the service request does not request a memory-management function, associates the request with a single-digit numeric category, and selects one of the mainframe computers as being able to most efficiently provide the requested service. The server then translates the service request into a configuration compatible with the selected mainframe and with a mainframe operating system running on the selected mainframe, and transmits the translated request to the selected mainframe. The server receives a result from the mainframe and translates the result into a configuration compatible with the application server computer, with the user application, and with a server operating system running on the application server computer.

Description:
This application is a continuation application claiming priority to Ser. No. 12/341,301, filed Dec. 22, 2008, now U.S. Pat. No. 8,458,466, issued Jun. 4, 2013. 
    
    
     FIELD OF THE INVENTION 
     The present invention discloses a system and associated method for efficiently combining high-end mainframe systems and lower-end server systems to provide stable and cost-effective computing environments. 
     BACKGROUND OF THE INVENTION 
     Mission-critical applications require stable and efficient computing environment. High-end mainframes are employed to stably host mission-critical applications. However, the high-end mainframes are prohibitively expensive to perform computation-intensive applications. Consequently, lower-end servers that primarily execute computation-intensive applications are often combined with high-end mainframes to provide both stability and computing performance at a reasonable cost. However, issues regarding system integration, application migration, system management and administration must be solved to interconnect two types of platforms. 
     Thus, there is a need for a system and associated method that efficiently interconnect high-end mainframes and lower-end servers. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for handling a system call in a hybrid system, the method comprising: 
     receiving a request to execute the system call from a user application running on a first computer system, wherein the system call provides a kernel service upon being executed, wherein the hybrid system comprises the first computer system and a second computer system, the first computer system comprising the user application and a first kernel, the second computer system comprising a second kernel, and wherein the first kernel is coupled to the second kernel; 
     discovering that the system call is predetermined to be remotely executed on the second computer system of the hybrid system; 
     converting the system call into a second configuration that is compatible with the second computer system such that the second kernel executes the converted system call to provide the kernel service to the user application; 
     transferring the converted system call to the second kernel; 
     obtaining a result of executing the converted system call, wherein the result is produced by the second kernel; 
     adjusting the obtained result to generate an adjusted result such that the adjusted result is in a first configuration that is compatible with the first computer system; and 
     sending the adjusted result to the user application that had sent the request, 
     wherein said receiving, said discovering, said converting, said transferring, said obtaining, said adjusting, and said sending are performed by the first kernel. 
     The present invention provides a computer program product, comprising a computer usable storage medium having a computer readable program code embodied therein, said computer readable program code containing instructions that when executed by a processor of a computer system implement a method for handling a system call in a hybrid system, the method comprising: 
     receiving a request to execute the system call from a user application running on a first computer system, wherein the system call provides a kernel service upon being executed, wherein the hybrid system comprises the first computer system and a second computer system, the first computer system comprising the user application and a first kernel, the second computer system comprising a second kernel, and wherein the first kernel is coupled to the second kernel; 
     discovering that the system call is predetermined to be remotely executed on the second computer system of the hybrid system; 
     converting the system call into a second configuration that is compatible with the second computer system such that the second kernel executes the converted system call to provide the kernel service to the user application; 
     transferring the converted system call to the second kernel; 
     obtaining a result of executing the converted system call, wherein the result is produced by the second kernel; 
     adjusting the obtained result to generate an adjusted result such that the adjusted result is in a first configuration that is compatible with the first computer system; and 
     sending the adjusted result to the user application that had sent the request, 
     wherein said receiving, said discovering, said converting, said transferring, said obtaining, said adjusting, and said sending are performed by the first kernel. 
     The present invention provides a system comprising a processor and a computer readable memory unit coupled to the processor, said memory unit containing instructions that when executed by the processor implement a method for handling a system call in a hybrid system, the method comprising: 
     receiving a request to execute the system call from a user application running on a first computer system, wherein the system call provides a kernel service upon being executed, wherein the hybrid system comprises the first computer system and a second computer system, the first computer system comprising the user application and a first kernel, the second computer system comprising a second kernel, and wherein the first kernel is coupled to the second kernel; 
     discovering that the system call is predetermined to be remotely executed on the second computer system of the hybrid system; 
     converting the system call into a second configuration that is compatible with the second computer system such that the second kernel executes the converted system call to provide the kernel service to the user application; 
     transferring the converted system call to the second kernel; 
     obtaining a result of executing the converted system call, wherein the result is produced by the second kernel; 
     adjusting the obtained result to generate an adjusted result such that the adjusted result is in a first configuration that is compatible with the first computer system; and 
     sending the adjusted result to the user application that had sent the request, 
     wherein said receiving, said discovering, said converting, said transferring, said obtaining, said adjusting, and said sending are performed by the first kernel. 
     The present invention provides a method and system that overcomes at least one of the current disadvantages of conventional method and system for providing kernel services in a hybrid system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a hybrid system that integrates two architecturally different systems respectively comprising kernels U and K at kernel levels, in accordance with embodiments of the present invention. 
         FIG. 2A  is a flowchart depicting a method for handling a system call by the kernel U in the hybrid system of  FIG. 1 , in accordance with the embodiments of the present invention. 
         FIG. 2B  is a flowchart depicting a method for handling a system call by the kernel K in the hybrid system of  FIG. 1 , in accordance with the embodiments of the present invention. 
         FIG. 3  illustrates a computer system used for handling a cross-platform system call in the hybrid system, in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a hybrid system  100  that integrates two architecturally different systems respectively comprising kernels U and K at kernel levels, in accordance with embodiments of the present invention. 
     The hybrid system  100  comprises at least one system U and a system K  150  interconnected through a data path  180 . A system U  110  of said at least one system U is a lower-end server that is configured to primarily execute user applications that have intensive computation workloads in the hybrid system  100 . The system K  150  is a high-end mainframe that is configured to primarily execute kernel services for the hybrid system  100 . The system U  150  and the system K  150  operate on respective hardware platforms and have respective software environments that have convertible system calls for respective kernels. The system U  150  and the system K  150  communicate with each other through the data path  180  that interconnects their respective kernels. The hybrid system  100  is configured to be perceived by users as a single system that provides functionalities and characteristics of both the system U  110  and the system K  150 . 
     The system U  110  is the lower-end server that is configured to primarily execute user applications for both the system U  110  and the system K  150  in the hybrid system  100 . The system U  110  comprises at least one user application U and a kernel U  130 . 
     A user application  120  of said at least one user application U is a user mode executable code of the system U  110 . When the user application  120  needs a kernel service, the user application  120  invokes a system call U  119  to interfaces with the kernel U  110 . The system call U  119  requests a service provided by the kernel U  130  and/or by the kernel K  170 . 
     The kernel U  130  is a main part of an operating system that controls the system U  110 . The operating system provides services such as, inter alia, time/clock related services, memory management services, process management services including scheduling, termination, and signalling, data services such as file/file system operations, network operations, and I/O calls, debugging and logging functionalities, inter-process communication (IPC) services without a shared memory, memory sharing services, I/O synchronizations, system administration services, and hardware services, etc. Examples of the operating system may be, inter alia, Linux, UNIX®, etc. (UNIX is a registered trademark of X/Open Company Ltd., in the United States and other countries.) 
     The kernel U  130 , among other operating system functionalities, specifically refers to a system call handling facility of the system U  110  throughout this specification. The kernel U  130  comprises a receiver  131 , a splitter  132 , a converter  133 , a transporter  134 , and a local system call handler  135 , which are functional components rather than physically separated units. 
     The receiver  131  is an interface between a system call  119  invoked from the user application  120  and the kernel U  130 . The system call  119  is serviced by the system U  110  and/or the system K  150 . The receiver  131  sends the received system call  119  to the splitter  132 . 
     The splitter  132  determines whether the received system call  119  is either a local system call of the system U  110  or a remote system call of the system K  150 . The splitter  132  forwards the local system call to the local system call handler  135  and the remote system call to the converter  133 . 
     In one embodiment of the present invention, examples of local system calls are, inter alia, a clock request system call of the user application  120  that does not need to be synchronized with the system K  150 , a memory management system call such as mprotect( ) that modifies swapping properties of the user application, etc. 
     In the same embodiment of the present invention, examples of remote system calls are, inter alia, time related services, process/signal management services, file/file system operations, network operations, I/O devices accesses, debugging and logging functionalities, inter-process communication (IPC) services without a shared memory, a shared memory, etc. 
     The converter  133  converts the received remote system call to a corresponding system K system call that is executable on the system K  150 . The converter  133  also converts a result of executing the corresponding system K system call returned from the system K  150  to a corresponding result for the system U  110  to provide the corresponding result to the user application  120 . 
     System calls of the system U  110  and system calls of the system K  150  are previously mapped according to their respective functionalities. Examples of issues to be addressed by the converter  133  may be, inter alia, a possible difference in endianness between the system U  110  and the system K  150 , memory mappings, etc. 
     The transporter  134  sends the converted corresponding system K system call from the system U  110  to the system K  150 . After the system call is executed on the system K  150 , the transporter  134  receives a result of the converted corresponding system K system call from the system K  150 . 
     The local system call handler  135  executes the local system call received from the splitter  132  and returns a result to the user application  120  that had invoked the system call. 
     The system K  150  is, as noted, the high-end mainframe that is configured to primarily execute kernel services for both the system U  110  and the system K  150  in the hybrid system  100 . The system K  150  comprises at least one user application K and a kernel K  170 . 
     The kernel K  170  is a core of an operating system that controls the system K  150 .  110 . See description of the kernel U  130 , supra, for services provided by the operating system. The kernel K  170  comprises a system call handler K  171 . 
     The system call handler K  171  receives a system call request from the transporter  134  of the system U  110  through the data path  180 . The received system call request is serviced by the system call handler K  171 . After executing the system call request, the system call handler K  171  returns a result to the transporter of the system U  110  through the data path  180 . The system call handler K  171  controls an I/O device driver that handles an input/output (I/O) request that is directed to an I/O device that is controlled by the system K  150 . In the hybrid system  100 , the kernel K  170  services all I/O requests from both the system U  110  and the system K  150 . Examples of the I/O device may be, inter alia, HiperSockets®, a direct access storage device (DASD), enterprise tape systems, etc. (HiperSockets is a registered trademark of International Business Machines Corporation in the United States and other countries.) 
     The data path  180  interconnects the transporter  134  of the kernel U  130  and the system call handler  171  of the kernel K  170 . The data path  180  directly connects the system U  110  and the system K  150  in a kernel level with a high-speed communication I/O device such as 10 Gigabit Ethernet. 
     In one embodiment of the present invention, the system U  110  is a blade server employing Intel® or AMD® processors and the system K  150  is an IBM® System z® mainframe. (Intel is a registered trademark of Intel Corporation in the United States and other countries; AMD is a registered trademark of Advanced Micro Devices, Inc in the United States and other countries; IBM and System z are registered trademarks of International Business Machines Corporation in the United States and other countries.) Both the blade server and the mainframe employ the Linux operating system or other UNIX family OS. The hybrid system  100  maintains input/output capability of the mainframe to HiperSockets, a direct access storage device (DASD), enterprise tape systems, etc. The hybrid system  100  retains superior hardware stability and management features of the mainframe. The hybrid system  100  also executes computation intensive applications on the blade server to achieve cost effectiveness. The hybrid system  100  provides a unified view of all resources for all applications on both the mainframe and the blade server. 
     The hybrid system  100  may be employed in areas of, inter alia, dynamic web servicing, data mining, SAP® R/3 application serving, Domino® groupware processing, application servicing and Java® processing. (SAP is a registered trademark of SAP AG in the United States and other countries; Domino is a registered trademark of International Business Machines Corporation in the United States and other countries; Java is a registered trademark of Sun Microsystems, Inc., in the United States and other countries.) 
       FIG. 2A  is a flowchart depicting a method for handling a system call by the kernel U in the hybrid system of  FIG. 1 , supra, in accordance with the embodiments of the present invention. 
     Initially, the user application runs in a user mode on the system U. To perform a kernel operation, the user application invokes a system call to interface with the kernel U of the system U. Upon invoking the system call, the user application passes control over to the kernel U, and the system U starts running in a kernel mode to handle the system call. 
     In step  210 U, the kernel U receives the system call request and parameters of the system call. The receiver of  FIG. 1 , supra, represents step  210 U, which may be a separate sub-procedure. The kernel U proceeds with step  220 U. 
     In step  220 U, the kernel U determines whether the system call should be executed remotely on the system K or whether the system call can be executed locally on the system U. If the kernel U determines that the system call can be executed remotely on the system K, then the system call handler of the kernel U proceeds with step  230 U. If the kernel U determines that the system call can be executed locally on the system U, then the kernel U proceeds with step  270 U. 
     In one embodiment of the present invention, the kernel U uses a predefined number scheme for each system call in determining whether the system call is remote or local in step  220 U. Each system call and required parameters for each system call are analyzed and assigned a respective number describing a function of the system call. Examples of system call numbering based on the function of each system call may be, inter alia, {1=write, 2=read, 3=fork, 4=get-time-of-day, . . . }, etc. Based on the assigned number and necessary parameters of the system call, the kernel U determines whether to execute the system call either locally or remotely. 
     For more effective and seamless integration of the system U and the system K, this embodiment locally executes memory management services and remotely executes time-related services, process/signal management services, scheduling services, file and file system operations, network operations, I/O calls, debugging and logging functionalities, inter-process communication (IPC) services without shared memory, and shared memory operations, etc. 
     There are certain system calls that require special/combined actions rather than simple remote/local execution. These actions are implementation specific and usually simulate the system call in a manner that provides services of the system call and satisfies system-specific requirements of both the kernel U and the kernel K. Examples of system calls require special actions may be, inter alia, I/O synchronizing system calls, exit( ) system call, administrative system calls, and hardware-specific system calls, etc. In cases of I/O synchronizing system calls such as sync( ), close( ), if there is no optimization of a shared page cache, these I/O synchronizing system calls will trigger synchronization of local dirty buffers of the system U to a disk through the system K, before the actual system call is performed remotely. Examples of administrative system calls are, inter alia, reboot( ), kernel module handling calls, virtualization system calls, etc. 
     In another embodiment, step  220 U determines that time-related system calls are locally executable on the system U. In this embodiment, only applications executed on the system U see the same time, or time services on the system U and the system K must be synchronized using existing technologies such as the Network Time Protocol (NTP) as specified in Request For Comments (RFC) 1305 by the Internet Engineering Task Force (IETF). 
     In another embodiment, step  220 U determines that file/file system, network and I/O calls as locally executable for all and/or part of resources to optimize performance of the hybrid system. To support such optimization, the view on all or some I/O resources that is locally serviced on the system U should be identical both on the system U and on the system K. In this embodiment, by using shared file systems and disks, the present invention performs inter-process communication (IPC) calls and/or shared memory locally on the system U. An example of shared file systems and disk devices may be, inter alia, the Global File System (GFS) on a shared Storage Area Network (SAN) device. Although this embodiment significantly increases performance for inter-process communication (IPC) and/or shared memory service calls, the inter-process communication (IPC) domain is restricted to the system U, rendering the hybrid system not completely transparent between the system U and the system K. However, in cases when all parts of an application doing inter-process communication (IPC) or using shared memory are executed on the system U, the performance gain can compensate the loss of transparency between the system U and the system K. These inter-process communication (IPC)/shared memory resources cannot be seen on the system K or other nodes. 
     In still another embodiment, step  220 U determines that limited number of process management calls should be locally executed. While remotely executing most of process management calls on the system K, this embodiment locally services, inter alia, the system call getpid( ) that requests an identifier (ID) of a process that is being used, because the system U locally has all the information available to service the getpid( ) system call and such local service of frequent process management system calls will optimize performance of the hybrid system. 
     In aforementioned embodiments, a notification can be sent to the system K from the system U to make the hybrid system transparent between the system U and the system K. Such notification can be used for system logs and/or debugging purposes. Also, aforementioned embodiments in determining whether a system call is local or remote can be used in combination with embodiments for other system calls in implementing the system U and/or the system K. 
     In step  230 U, the kernel U converts the system call and parameters associated with the system call into a corresponding system K system call and associated parameters for the converted corresponding system K system call, respectively. 
     System calls and parameters are inherent to a platform and a kernel on which system calls are executed. Thus, to provide a consistent result in cross-platform system call execution, the kernel U system call and the parameters must be converted to the kernel K system call and corresponding system K data before an execution. System calls in respective systems are mapped by number and/or function. The parameters are converted with respect to differences between the systems, inter alia, endianness, address space usage, pointers, namespace of object identifiers, memory object synchronization, etc. 
     Numeric parameters such as like integer values or bitmasks are converted to compensate for differences in internal representation of numbers called endianness. For example, if the system U is a little endian system and the system K is a big endian system, the numeric parameters of the system U system call will be reversed to match the endianness of the system K. 
     An example of a system call with numeric parameters may be, inter alia, kill( ), etc. The kill( ) system call has two integer parameters representing a process ID and a signal number to be sent to a process identified by the process ID. The system call number will be converted to match the kill( ) system call number on the system K. If the system U and the system K have different endianness, the process ID and the signal number are endian-converted. 
     When a parameter of the system call is a memory reference or a memory object, converting the parameter needs extra steps. When a pointer parameter refers to memory areas having raw data, the kernel U copies the referenced data to system K and converts the pointer parameter such that the converted pointer parameter can be associated with the copied raw data in the system K. Example of the raw data may be, inter alia, content of I/O operations, etc. Because the user space on the system U can refer to different pages from the kernel space for the system K, synchronizing system calls like sync( ) and/or close( ) require the kernel U to write dirty pages to the file before executing the sync( ) and/or close( ) system calls remotely on the system K. An example of a case when the user space on the system U refers to different pages from the kernel space for the system K may be, inter alia, when an application performs a memory map system call mmaps( ) upon a file into an address space of the system U. 
     An example of a system call with memory reference may be, inter alia, write( ). A Write( ) system call has three parameters representing a file descriptor that is an integer, a buffer area that is a pointer to a starting address of a memory area to write, and a length of the buffer area that is an integer representing the size of the buffer area to write. The system call number of the write( ) system call is converted to match the write( ) system call number on the system K. If the system U and the system K have different endianness, the file descriptor and the length of the buffer area are endian-converted. Data in the buffer area will be copied to the system K and the buffer area parameter is adjusted to point to the copied memory area in the system K. 
     For a system call having memory reference parameters, a memory area referred to by a parameter of the system call may be a structured object rather than raw data. For example, the ioctl( ) system call may have an object supporting a buffer interface. The structured object referred to by the parameter should be evaluated and converted element by element in the structured object pursuant to the usage of the parameter in the system call to execute the system call remotely on the system K. Each element in the structured object may be a numeric parameter, a memory reference with raw data, or a memory reference with a structured object. Each element in the structured object is converted as described in step  230 U. 
     In step  240 U, the kernel U transfers the system call request including all parameters and data to the system K through the data path, which are received by the kernel K in step  241 K of  FIG. 2B , infra. The kernel U proceeds with step  250 U. 
     In step  250 U, the kernel U receives results from the kernel K performing step  245 K of  FIG. 2B , infra. The kernel U proceeds with step  260 U. 
     In step  260 U, the kernel U adjusts the result received in step  250 U from the system K for the system U kernel and application. The adjustment in step  260 U is a reverse process of the conversion in step  230 U. Thus the adjustment in step  260 U also comprises reverse conversions of data due to little/big endian differences, reverse conversions of data, pointers, raw data, and/or structured data to be configured for the system U, reverse translations of namespaces from the system K to the system U, etc. Because the result received in step  250 U is executed on the system K, the result should be configured for the system U before the result is returned to the user application. 
     If the system call has an impact on structures of the kernel U, the kernel U structure is updated in step  260 U as a part of the adjustment. For example, if the system call is for signal or process management, a result of executing the system call changes processing environments of the system U in the kernel space and/or the user space. The kernel U proceeds with step  280 U. 
     In step  270 , the kernel U executes the system call locally on the system U as in a conventional single platform system consisting of the system U. The kernel U proceeds with step  280 U. 
     In step  280 , the kernel U returns the adjusted result from either step  260 U or step  270 U to the user application that had invoked the system call U. If any status updates resulting from executing the system call remotely on the system K need to be made available to the system U, the kernel U transmits such information regarding status updates to the system U prior to returning the control to the user application such that the user application on the system U obtains the result of the system service produced by executing the system call. The user application takes control of the thread of execution back from the kernel U and resumes the execution. 
       FIG. 2B  is a flowchart depicting a method for handling a system call by the kernel K in the hybrid system of  FIG. 1 , supra, in accordance with the embodiments of the present invention. 
     In step  241 K, the kernel K receives a system call request and parameters from the kernel U performing step  240 U of  FIG. 2A , supra. 
     In step  242 K, the kernel K determines whether the requested system call needs memory reference to execute the requested system call. If the requested system call has parameters referring to a memory space, the kernel U marks the system call for a memory reference during the conversion in step  230 U of  FIG. 2A , supra. Thus the kernel K determines that the requested system call needs a memory reference pursuant to the information received from the kernel U. If the kernel K determines that the requested system call needs a memory reference, the kernel K proceeds with step  243 K. If the kernel K determines that the requested system call does not need a memory reference, the kernel K proceeds with step  244 K. 
     In step  243 K, the kernel K finds a mapping associated with each memory reference parameter of the requested system call. The mappings associated with each memory pointer parameter is consistent with a result of converting memory reference parameters from the system U to system K, which was performed in step  230 U of  FIG. 2A , supra. The kernel K uses the mapping associated with each memory reference parameter to locate parameters of the requested system call on the system K. After this step, memory references point to data areas on system K, which have been referenced by the system call on system U and have been copied from the according data areas of system U in step  240 U. The kernel K proceeds to step  244 K. 
     In this embodiment, by converting memory reference parameters on the system U, the hybrid system shifts as much computation and/or workload as possible from the system K to the system U associated with executing a cross-platform system call. 
     In another embodiment of the present invention, the conversion of memory reference parameters in step  230 U on the system U and the mapping in step  243 K on the system K may be integrated into a conversion of memory reference parameters on the system K, after the kernel K received the requested system call and related parameters. In this embodiment, the hybrid system imposes more workload on the system K to execute a cross-platform system call to achieve a simpler implementation. 
     In step  244 K, the kernel K executes the requested system call with parameters that are configured for the kernel K. 
     In step  245 K, the kernel K sends a result from executing the requested system call to the kernel U. 
       FIG. 3  illustrates a computer system  90  used for handling a cross-platform system call in the hybrid system, in accordance with embodiments of the present invention. 
     The computer system  90  comprises a processor  91 , an input device  92  coupled to the processor  91 , an output device  93  coupled to the processor  91 , and memory devices  94  and  95  each coupled to the processor  91 . The input device  92  may be, inter alia, a keyboard, a mouse, a keypad, a touchscreen, a voice recognition device, a sensor, a network interface card (NIC), a Voice/video over Internet Protocol (VOIP) adapter, a wireless adapter, a telephone adapter, a dedicated circuit adapter, etc. The output device  93  may be, inter alia, a printer, a plotter, a computer screen, a magnetic tape, a removable hard disk, a floppy disk, a NIC, a VOIP adapter, a wireless adapter, a telephone adapter, a dedicated circuit adapter, an audio and/or visual signal generator, a light emitting diode (LED), etc. The memory devices  94  and  95  may be, inter alia, a cache, a dynamic random access memory (DRAM), a read-only memory (ROM), a hard disk, a floppy disk, a magnetic tape, an optical storage such as a compact disk (CD) or a digital video disk (DVD), etc. The memory device  95  includes a computer code  97  which is a computer program that comprises computer-executable instructions. The computer code  97  includes, inter alia, an algorithm used for handling a cross-platform system call in the hybrid system according to the present invention. The processor  91  executes the computer code  97 . The memory device  94  includes input data  96 . The input data  96  includes input required by the computer code  97 . The output device  93  displays output from the computer code  97 . Either or both memory devices  94  and  95  (or one or more additional memory devices not shown in  FIG. 3 ) may be used as a computer usable storage medium (or a computer readable storage medium or a program storage device) having a computer readable program embodied therein and/or having other data stored therein, wherein the computer readable program comprises the computer code  97 . Generally, a computer program product (or, alternatively, an article of manufacture) of the computer system  90  may comprise said computer usable storage medium (or said program storage device). 
     While  FIG. 3  shows the computer system  90  as a particular configuration of hardware and software, any configuration of hardware and software, as would be known to a person of ordinary skill in the art, may be utilized for the purposes stated supra in conjunction with the particular computer system  90  of  FIG. 3 . For example, the memory devices  94  and  95  may be portions of a single memory device rather than separate memory devices. 
     While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.