Abstract:
A computer system contains a revision indicator which is stored in a protected special area of computer memory. The revision indicator specifies the revision of the hardware actually present in the system. The revision indicator data is presented by the computer during power up so that a user may be aware of the type and configuration of the computer system hardware. The revision indicator may be displayed by the computer system BIOS during power on self test (POST), for example. The memory storing the revision indicator is protected from erroneous or unauthorized change.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to system level computer operation, and more specifically, to hardware identification measures for computer system software. 
     2. Description of the Related Art 
     As the computer industry has evolved, different versions of hardware and software have been introduced over time. For example, microprocessors, modems, and bus structures operate at much faster data rates than similar devices introduced only a few years ago. Software, one of the most rapidly developing areas of computer technology, however, often is compatible with only some versions of a particular hardware platform. In other situations, software has greater functionality with particular versions of a hardware platform than with other versions. 
     Because software developers generally cannot know precisely which version of a particular hardware platform will be used to run their products, software developers often write generic computer programs to run on all versions. However, modem hardware not only runs faster than in previous generations; additional features, not available on previous versions, allow functionality unimaginable by programmers only a few years ago. Software meant to run optimally across several generations of hardware cannot take advantage of specialized features of a particular hardware platform, unless those features are available on all versions. Consequently, some features cannot be accessed by software. 
     This lowest common denominator problem appears only to be getting more problematic. As software development moves toward cross-platform portable code (for example, on Internet-driven Java-based virtual machines) hardware platforms become less visible to the software. Some software loses backward-compatibility, engendering hostility in paying customers who have already made significant hardware investments now rendered obsolete by the quantum advance in the software evolution. Other software is marketed toward only those customers who have the latest version of the hardware platform, limiting the software&#39;s ability to appeal to the wider market. 
     Software, particularly software directed to a particular virtual machine, therefore, often under-performs by failing to take advantage of functional features presented by the latest actual hardware, since the software is designed to run on any version. Alternatively, software performs with full-feature platform-specific richness, but excludes large portions of the otherwise interested software-purchasing market. Moreover, the latter type of software becomes obsolete if the hardware platform ever falls into disfavor. 
     Many computer systems do contain hardware-encoded revision information, encoded by placing pull-up and pull-down resistors and a shift register motherboard. The resistors have typically loaded a value into the shift register when power is applied to the system. This method is effective, but difficult to update once the computer system has been provided to an end user or even to a VAR (value added reseller). Moreover, the resistor and the shift register cost money and occupied valuable board space. 
     An additional problem is the difficulty of upgrading all computer systems manufactured across an enterprise. Because the resistor and register approach is a hardware implementation system, changes have required physical substitutions or changes, or other time-intensive system-by-system manipulation, 
     SUMMARY OF THE INVENTION 
     Briefly, the present invention allows manufacturing entities to place a “revision indicator” in a special area of memory that cannot be altered. The revision indicator is stored in a region of memory not available to the user. The protected area is a flash memory, which must be physically removed to be reprogrammed. 
     A person must physically remove the memory device containing the revision indicator, place the revision indicator memory in an external device that is not part of the computer system, and apply external voltages and currents not available within the computer system to the memory in order to change the revision indicator. 
     When a user powers on the computer system, the revision indicator is presented to the basic input/output system or BIOS, and is available while the boot software is running. For example, the revision indicator may be presented during the installation and execution of the Basic Input Output System (BIOS), Power on Self Test (POST), and operating system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention can be obtained when the following detailed description of the preferred embodiment is considered in conjunction with the following drawings, in which 
     FIG. 1 is a schematic block diagram of a computer system according to the present invention. 
     FIG. 2 is a schematic diagram of flash ROM components of the computer system of FIG.  1 . 
     FIG. 3 is a block diagram of components initialized by a boot block in the computer system of FIG.  1 . 
     FIG. 4 is a schematic diagram of components of the computer system of FIG. 1 having multiple slots for connecting memory devices. 
     FIG. 5 shows a flowchart of a boot process according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following disclosures are hereby incorporated by reference: 
     U.S. application Ser. No. 09/071,127, entitled “A COMPUTER METHOD AND APPARATUS TO FORCE BOOT BLOCK RECOVERY,” by Don R. James, Jr., Randall L. Hess, and Jeffrey D. Kane, filed Apr. 30, 1998; 
     U.S. application Ser. No. 09/070,821, entitled “BOOT BLOCK SUPPORT FOR ATAPI REMOVABLE MEDIA DEVICES,” by Paul J. Broyles and Don R James, Jr., filed Apr. 30, 1998; 
     U.S. application Ser. No. 09/070,475, entitled “SECURITY METHODOLOGY FOR DEVICES HAVING PLUG AND PLAY CAPABILITIES,” by Christopher E. Simonich and Robin T. Tran, filed Apr. 30, 1998; 
     U.S. application Ser. No. 09/070,942, entitled “METHOD AND APPARATUS FOR REMOTE ROM FLASHING AND SECURITY MANAGEMENT FOR A COMPUTER SYSTEM,” by Manuel Novoa, Paul H. McCann, Adrian Chrisan. and Wayne P. Sharurn, filed Apr. 30, 1998; 
     U.S. application Ser. No. 09/070,866, entitled “A METHOD FOR FLASHING ESCD AND VARIABLES INTO A ROM,” by Mark A. Piwonka, Louis B. Hobson, Jeff D. Kane, and Randall L. Hess, filed Apr. 30, 1998; 
     U.S. application Ser. No. 08/684,413, entitled “FLASH ROM PROGRAMING,” by Patrick R. Cooper, David J. Delisle, and Hung Q. Le filed Jul. 19, 1996; and 
     U.S. application Ser. No. 09/071,128, entitled “A UNIFIED PASSWORD PROMPT OF A COMPUTER SYSTEM,” by Michael D. Garrett, Randall L. Hess, Chi W. So, Mohammed Anwarmariz, filed Apr. 30, 1998; 
     U.S. application Ser. No. 09/123,658, entitled “OWNERSHIP TAG ON POWER-UP SCREEN,” by Paul J. Broyles, m, Rahul G. Patel and Mark A. Piwonka, filed of even date herewith; and 
     U.S. application Ser. No. 09/123,307, entitled “COMPUTER SYSTEM WITH POST SCREEN FORMAT CONFIGURABILITY,” by Rahul J. Patel and Paul J. Broyles, III, filed concurrently herewith, all of which are assigned to the assignee of this invention. 
     COMPUTER SYSTEM OVERVIEW 
     Turning to FIG. 1, illustrated is a typical computer system S implemented according to the invention. While this system is illustrative of one embodiment, the techniques according to the invention can be implemented in a wide variety of systems. The computer system S in the illustrated embodiment is a PCI bus/ISA bus based machine, having a peripheral component interconnect (PCI) bus  10  and an industry standard architecture (ISA) bus  12 . The PCI bus  10  is controlled by PCI controller circuitry located within a memory/accelerated graphics port (AGP)/PCI controller  14 . This controller  14  (the “host bridge”) couples the PCI bus  10  to a processor socket  16  via a host bus, an AGP connector  18 , a memory subsystem  20 , and an AGP  22 . A second bridge circuit, a PCI/ISA bridge  24  (the “ISA bridge”) bridges between the PCI bus and the ISA bus  12 . 
     The host bridge  14  in the disclosed embodiment is a 440LX Integrated Circuit by Intel Corporation, also known as the PCI AGP Controller (PAC). The ISA bridge  24  is a PIIX 4 , also by Intel Corporation. The host bridge  14  and ISA bridge  24  provide capabilities other than bridging between the processor socket  16  and the PCI bus  10 , and the PCI bus  10  and the ISA bus  12 . Specifically, the disclosed host bridge  14  includes interface circuitry for the AGP connector  18 , the memory subsystem  20 , and the AGP  22 . The ISA bridge  24  further includes an internal enhanced WDE controller for controlling up to four enhanced IDE drives  26 , and a universal serial bus (USB) controller for controlling USB ports  28 . 
     The host bridge  14  is preferably coupled to the processor socket  16 , which is preferably designed to receive a Pentium II processor module  30 , which in turn includes a microprocessor core  32  and a level two (L 2 ) cache  34 . The processor socket  16  could be replaced with different processors other than the Pentium II without detracting from the spirit of the invention. 
     The host bridge  14 , when the Intel 440LX North Bridge is employed, supports extended data out (DO) dynamic random access memory (DRAM) and synchronous DRAM (SDRAM), a 64/72-bit data path memory, a maximum memory capacity of one gigabyte, dual inline memory module (DIMM) presence detect, eight row address strobe (RAS) lines, error correcting code (ECC) with single and multiple bit error detection, read-around-write with host for PCI reads, and 3.3 volt DRAMs. The host bridge  14  support up to 66 megahertz DRAMs, whereas the processor socket  16  can support various integral and nonintegral multiples of that speed. 
     The ISA bridge  24  also includes enhanced power management. It supports a PCI bus at 30 or 33 megahertz and an ISA bus  12  at ¼ of the PCI bus frequency. PCI revision 2.1 is supported with both positive and subtractive decode. The standard personal computer input/output (I/O) functions are supported, including a dynamic memory access (DMA) controller, two 82C59 interrupt controllers, an 8254 timer, a real time clock (RTC) with a 256 byte complementary metal oxide semiconductor (CMOS) static RAM (SRAM), and chip selects for system read only memory (ROM), real time clock (RTC), keyboard controller, an external microcontroller, and two general purpose devices. The enhanced power management within the ISA bridge  24  includes full clock control, device management, suspend and resume logic, advanced configuration and power interface (ACPI), and system management bus (SUMus) control, which implement the inter-integrated circuit (I 2 C) protocol. 
     The PCI bus  10  couples a variety of devices that generally take advantage of a high speed data path. This includes a small computer system interface (SCSI) controller  26 , with both an internal port  38  and an external port  40 . In the disclosed embodiment, the SCSI controller  26  is a AIC-7860 SCSI controller. Also coupled to the PCI bus  10  is a network interface controller (NIC)  42 , which preferably supports the ThunderLan™ power management specification by Texas Instruments. The NIC  42  is coupled through a physical layer  44  and a filter  46  to an RJ 45  jack  48 , and through a filter  50  to a AUI jack  52 . 
     Between the PCI Bus  10  and the ISA Bus  12 , an ISA/PCI backplane  54  is provided which include a number of PCI and ISA slots. This allows ISA cards or PCI cards to be installed into the system for added functionality. 
     Further coupled to the ISA Bus  12  is an enhanced sound system chip (ESS)  56 , which provides sound management through an audio in port  58  and an audio out port  60 . The ISA bus  12  also couples the ISA bridge  24  to a Super I/O chip  62 , which in the disclosed embodiment is a National Semiconductor Corporation PC87307VUL device. This Super I/O chip  62  provides a variety of input/output functionality, including a parallel port  64 , an infrared port  66 , a keyboard controller for a keyboard  68 , a mouse port for a mouse port  70 , additional series ports  72 , and a floppy disk drive controller for a floppy disk drive  74 . These devices are coupled through connectors to the Super I/O  62 . 
     The ISA bus  12  is also coupled through bus transceivers  76  to a flash ROM  78 , which can include both basic input/output system (BIOS) code for execution by the processor  32 , as well as an additional code for execution by microcontrollers in a ROM-sharing arrangement. 
     The ISA bus  12  further couples the ISA bridge  24  to a security, power, ACPL and miscellaneous application specific integrated circuit (ASIC)  80 , which provides a variety of miscellaneous functions for the system. The ASIC  80  includes security features, system power control, light emitting diode (LED) control a PCI arbiter, remote wake up logic, system fan control, hood lock control, ACPI registers and support, system temperature control, and various glue logic. 
     Finally, a video display  82  can be coupled to the AGP connector  18  through an AGP master or video card  150  for display of data by the computer system S. The video display  82  displays video and graphics data provided by a video display process running on either the processor module  30  or another by a PCI device bus master or PCI bridge device bus master via host bridge  14 . Video or graphics data may be stored in main memory or in a supplementary or extension memory module. Again, a wide variety of systems could be used instead of the disclosed system S without detracting from the spirit of the invention. 
     According to the present invention, certain memory locations, such as indicated at  202  (FIG. 2) in the flash ROM  78 , having additional protection from alteration contain a revision indicator. The revision indicator so stored identifies the version of the hardware platform of computer system S. When processor module  30  is booted, a basic input output system (BIOS) is loaded and executed on processor module  30 . According to the present invention, a processor associated with the BIOS obtains the revision indicator from the protected area of memory and displays the revision indicator on display  82 . 
     THE FLASH ROM BOOT BLOCK 
     Turning now to FIG. 2, a sector partitioning structure  200  of the flash ROM  78  in the disclosed embodiment is shown. However, while this diagram is illustrative of one embodiment, the techniques according to the invention can be implemented in a variety of embodiments and can be implemented with a variety of non-volatile memory. The sector partitioning structure  200  is determined by the sector architecture of the particular flash ROM  78 . The flash ROM  78  used in the disclosed embodiment is an Advanced Micro Devices (AMD) AM29F002 flash ROM memory. The sector partitioning structure  200  shows a top boot block design architecture. The Advanced Micro Devices AM29F002 flash ROM memory can also be implemented with a bottom boot block design architecture. 
     A boot block sector  202  consists of a first boot block sector  204  of 16 kilobytes and a second boot block sector  206  of 8 kilobytes. The remaining 232 kilobytes form a system block  208  divided into 5 sectors  210 - 218 . In the disclosed embodiment, the first sector  210  has 8 kilobytes, the second sector  212  has 32 kilobytes, and the remaining three sectors  214 ,  216 , and  218  have 64 kilobytes equally. The code stored in the system block  208  preferably contains the Basic Input/Output System (BIOS) code. The BIOS is code interfacing between the operating system and the specific hardware configuration, allowing the same operating system to be used with different hardware configurations. The boot block  202  contains the code necessary to initialize the systems when an anomaly during power-up is detected. During a boot block  202  initialization, preferably a reduced set of hardware is initialized, thus reducing the size of the code in the boot block  202 . The boot block  202  code typically contains an initialization procedure for only the hardware necessary to perform limited functions. Typically a limited function necessary to be performed during boot block  202  initialization is the flash of the ROM  78 . The boot block  202 , according to the invention, contains code initializing the hardware components necessary to flash the ROM  78  and to prompt the user for an administrative password. The boot block  202  code is contained within the boot block  202 , which is protected from spurious initialization. 
     The boot block  202  is stored in a region or protected area of memory not available to the user. Such a protected area is a flash memory which must be physically removed to be reprogrammed. A person must physically remove the boot block  202  containing the revision indicator and place that memory device in an external device to the computer system to reprogram it. Further, such a memory device is preferably one which for reprogramming requires voltage or current devices not available within the computer system S. In this way, the memory containing the revision indicator cannot be inadvertently reprogrammed while in the computer system. 
     The boot block is an additional portion of ROM code within the ROM  78  that is executed at system reset. The boot block contains a validation portion and a boot portion. Upon system reset, the validation portion performs a validation check on the system ROM  78  itself and either jumps to the normal system ROM code or to the boot portion, depending upon the result of the validation check (See step  500  of FIG. 5.) The boot portion, although not capable of initializing any add-in devices except IDE&#39;s, does contain enough code to allow a system administrator to flash a valid ROM code into ROM  78  from a diskette. The boot block is physically located within the ROM to be accessed by the reset vector. The flash ROM  78  contains a 16 KB sector, two 8 KB sectors, a 32 KB sector, and three 64 KB sectors. The boot block occupies the first two sectors (totaling 24 KB), and is followed by an 8 KB ESCD sector, a reserved 32 KB sectors, a 64 KB sector containing normal-mode ROM code, 64 KB of compressed data, and 64 KB of CPU BIOS update code. The boot block  202  code typically is small in relation to the system block  208  code. 
     The BIOS has no access to the screen, so uses the various keyboard LEDS (such as Caps Lock, Num Lock and Scroll Lock) to report states and error information. 
     According to the present invention, the revision indicator is stored in a protected area of flash ROM. The revision indicator is placed in the boot block sector  202  in flash ROM  78  at the factory during the manufacturing process. The board revision information is preferably placed into the binary ROM image at a specified physical location (3FFD4b into buffer, for example) before the ROM  78  is flashed and the boot block sector  202  is protected. 
     Since the revision indicator is placed in the boot block sector  202  of flash ROM  78 , the information is not flashable. Further, the boot block  202  exists as a secondary mechanism for bad ROM flashes. 
     Turning to FIG. 3, illustrated is a block diagram  300  of components of the system S that are initialized by the boot block  202 . The processor  32  copies the system block code  208  from the ROM  78  into RAM, creating the ROM image, and then executes the system block  208  code, including the boot block  202  code contained in the ROM image. The processor  32 , during initial power up and execution of boot block  202  code, executes the validation portion to determine if the flash ROM  78  has become corrupt. If the flash ROM  78  is corrupt, then the processor  32  executes the boot portion of the boot block to allow an administrator to re-flash portions of the boot block  202  code from a diskette. Also, during initial power up, when reflashing is not needed, the Super I/O device  62  and the security device  80  are initialized by the processor  32 . BIOS code is also loaded from the ROM into RAM. Upon initialization of the Super I/O device  62 , the system board revision resident in boot block  202  is provided to the BIOS and stored in NVRAM for use during routine/OS. 
     Whichever boot code the validation portion determines to use is loaded into RAM (volatile memory). The RAM is faster than the ROM itself When power is applied to the system, the BIOS is booted from the ROM, via the image. The BIOS then attempts to complete system initialization in normal mode unless interrupted during initialization. BIOS execution continues from the RAM and, upon conclusion, launches the operating system. 
     The revision indicator indicates the revision of the hardware platform of the computer system. A user operating the computer system can access the location of the CMOS containing the revision indicator, but does not know where in boot block memory it is located. The revision indicator in CMOS is accessible and not protected. If it is accessed in CMOS and modified, this is not a problem. On the next computer boot operation, the CMOS contents as modified will be replaced by an override during boot. 
     THE NVRAM BLACK BOX 
     Turning now to FIG. 4, black box or security device  80  and NVRAM of the super I/O chip  62  are shown in greater detail. The black box is nonvolatile RAM (NVRAM) that is composed of CMOS, yet is accessible only to the BIOS and the operating system (not to any other software running on the computer system). The black box is a protected region within the NVRAM that is writeable only by the BIOS, and readable only by the BIOS and by the operating system. NVRAM is typically provided with back-up batteries to prevent power loss. The BIOS accesses the CMOS by generating an Int 15h followed by the location within CMOS and, if the access is write enabled, data to be written to the CMOS location. This process is described below with respect to boot access to the revision number. With the present invention, the device  80  is of interest because of its storage of revision number information. 
     The memory security device  80  of FIG. 4 functions to lock and unlock resources within the computer system S, having multiple slots for connecting memory devices. The memory security device  80  of FIG. 4 includes three slots, numbered 0 through 2, each protected according to a different methodology. The contents of the memory devices connected to each security device  80  are accessible only to memory access requests complying with the corresponding methodology. Each slot of device  80  has two states: a locked state, in which data is protected, and an unlocked state. In the locked state, access is denied to the memory device connected to the corresponding slot. To transition to the locked state, a user must enter a “protect resources” command. To transition to unlocked state, transitioning the slot from the locked state, an “access resources” command must be issued, followed by a correct password. 
     Slot  0  of device  80  includes a flash ROM interface connecting to a flash ROM device. Slot  0  protects the flash ROM  78  from unauthorized writes such as viruses and unauthorized individuals. At power-up, the BIOS loads a flash ROM password into slot  0  and executes the “protect resources” command for that slot. After the system S has completed the boot process and before any other software is loaded, the BIOS issues a “protect resources” command to slot  0 , disabling further access to the flash ROM  78 . 
     Slot  1  of device  80  contains the “power-on” password of the user. The security device  80  communicates with the super I/O chip  62  containing the CMOS, by holding a “SIOAEN” and/or a “SIOWCL” signal to keep the super I/O chip  62  from decoding read and/or write cycles to the “power-on” password locations in the CMOS. The AEN signal is derived from ANDing a signal indicating that the black box slot  1  is locked and a signal indicating that the last data write to a real time clock index register was in the “power-on” password range, indicating that the user has missed an opportunity to access the “power-on” password location within. Thus, the security device  80  controls access to the CMOS within the super I/O chip  62 . The slot  1  of the black box selectively disables access to the “power on” password storage area within the CMOS. In contrast, the SIOWCL signal operates similarly to the SIOAEN signal, although the SIOWCL signal only prohibits writes and does not prohibit reads to the password. Thus, the SIOWCL signal may be used during subsequent user sessions to determine whether the user password has been entered correctly. 
     Slot  2  of the security device  80  is accessible only with an administrator password. The limited access of the slot  2  memory device protects system resource information that must be protected to preserve the integrity of the computer system. The administrator password is necessary to access particular registers of CMOS region  404 . The unlocking of slot  2 , however, also unlocks slot  1 , allowing an administrator cognizant of the administrator password to access these CMOS locations. Thus, the administrator has control of these memory locations in the computer system. It is recommended that, prior to unlocking slot  2 , the administrator check the status of slot  1  to see if it is locked, since relocking slot  2  does not re-lock slot  1 . 
     THE BOOT PROCESS 
     AS shown in FIG. 5, at step  500 , computer system S starts the boot process. The system block code is loaded from either the boot portion of the boot block or the normal system ROM image, depending on the result of the ROM image validation. The former case merely allows rehashing of the ROM  78 , if a diskette is present and the proper passwords are entered. The latter case, the normal system ROM operation, is of primary interest. 
     After the start routine  500 , of the system S is initialized during step  505  next operation is during step  510  where the board revision indicator is read from the boot block of flash ROM  78 . The board revision indicator is then stored in CMOS during step  515 . Control is then transferred to step  520  where the remaining, conventional steps of the BIOS routine are completed. 
     The BIOS typically identifies an Initial Program Load (IPL) device containing additional software, including the operating system (or OS). Generally, the operating system is located on a hard drive, while the BIOS typically resides in the system ROM  78 . The BIOS loads, initializes, and begins execution of the operating system and transfers control over to the operating system once the BIOS determines that the operating system has loaded correctly. The BIOS, however, does not terminate once the operating system is loaded; rather, the operating system is able to call various BIOS-related routines during run-time. 
     The operating system is then executed allowing a user to load and run user applications. The user applications often are commercially-available programs that a user has purchased and installed on the computer system. The operating system loads and installs the applications, and begins execution of the application, when commanded to do so by a user. 
     According to the present invention, the BIOS includes an instruction  530  or set of instructions for reading a revision number from a nonvolatile memory location, for example in a nonvolatile storage device such as the system ROM  78  or other flash ROM. The revision number indicates what features are available on the computer system hardware platform. The BIOS instruction or instructions also make the revision number available to the operating system and to software applications. Thus, software applications and operating systems are enhanced in their ability to take advantage of computer features. Thereafter, operations of the computer system S may proceed in the normal manner. 
     BOOT ACCESS TO REVISION NUMBER 
     BIOS code is code loaded from the ROM image that allows the computer system to begin operation, validate hardware, perform certain platform-specific operations, and then launch an operating system. Many device-specific commands from the subsequently-loaded operating system rely on information loaded by the BIOS and on routines left in memory by the BIOS. 
     The BIOS and the operating system gain access to the CMOS of the NVRAM by loading a sequence of values into particular registers and generating a particular interrupt after each value. 
     Generating an Int 15h interrupt with AX set to E823h allows access to CMOS. When BH is set to one, the access is a write access, and when BH is reset to zero, the access is a read access. Generating an Int 15h with AX set to E841h causes default values to be written from the ROM to NVRAM. 
     The BIOS may obtain the revision number by generating an Int 15h OE814h function. When Int 15h is generated while E814h is contained in the AX register, the revision level is returned in the BL register. The CF flag and the AH register indicate whether the revision number has been successfully obtained. When CF=0 (the carry flag is cleared) and AH=00h, the revision number has been successfully returned, and when CF=1 (the carry flag is set) and AH=86h, the revision number has not been successfully returned. 
     An example code for retrieving revision number information is set forth below: 
     mov ax,0E845h 
     int 15h 
     A suitable code for copying the board revision indicator from the boot block sector  202  at 4 GB to NVRAM or CMOS is the following: 
     
       
         
               
               
               
             
           
               
                   
               
             
             
               
                 CopyAutoRev 
                 proc 
                 near 
               
               
                 pushad 
                   
                   
               
               
                 push 
                 es 
               
               
                 push 
                 ds 
               
               
                 call 
                 GoProtectedMode 
                 ;Enter 4GB mode &amp; 
               
               
                   
                   
                 Enable A20 
               
               
                 mov 
                 ebx,BB_AUTOREV 
                 ;AutoRev addr in Boot Block 
               
               
                 mov 
                 bl,[ebx] 
                 ;get AutoReg byte 
               
               
                 mov 
                 ax,CMOS_AUTOREV 
                 ; 
               
               
                 call 
                 rnvsWrite 
                 ;save it in CMOS 
               
               
                 call 
                 GoRealMode 
                 ;return to Real Mode 
               
               
                 pop 
                 ds 
               
               
                 pop 
                 es 
               
               
                 popad 
               
               
                 ret 
               
               
                 CopyAutoRev 
                 endp 
               
               
                   
               
             
          
         
       
     
     With the present invention, the ROM  78  thus simply reads the revision indicator information from its own boot block memory  202 . Preferably, this may be aliased under 4 GB, the top of addressable memory, at fixed location 0FFFFFFD4h) during POST. ROM  78  copies this revision indicator data to CMOS during POST so that it can be referenced at run time. This is done without the need for special protected-mode selectors. ROM  78  then can make the revision indicator data available to software of computer system S through BIOS calls in the conventional manner. 
     Cross-platform applications are actually enhanced by the present invention. Applications intended to run a particular virtual machine can be easily altered to conform to the specificity of the physical machine. Applications can be altered slightly to read the revision number made available by the BIOS instructions, and enable and disable routines accordingly. Thus, the same software can be run on almost any version of hardware platform, without losing the ability to take advantage of platform-specific and revision-specific features. 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in number of variables, number of parameters, order of steps, field sizes, data types, code elements, code size, connections, components, and materials, as well as in the details of the illustrated hardware and software and construction and method of operation may be made without departing from the spirit of the invention.