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USER DOCUMENTATION FOR POV-Ray FOR MS-DOS USING WATCOM VERSION 1.0 Introduction The Watcom compiled version of POV-Ray is designated by either ".msdos.wat-cwa" or ".msdos.wat-d4g" after the POV-Ray version number on the opening banner. Everything in this document ONLY applies to that version. Other versions will operate under different rules. This file is NOT the only documentation for POV-Ray. There is a file called POVMSDOS.DOC which covers the MSDOS-specific features but that still isn't everything. There is a hypertext utility POVHELP.EXE that reads a file POVHELP.PHE which contains the main documentation for POV-Ray itself that is common to all versions. This version has been compiled as a 32-bit DOS protected mode application. It must be run on a 386 or higher system with at least 4 meg of memory. More memory is preferred. The program uses one of two different DOS extenders to manage memory and to create and use virtual memory swap files. The "wat-cwa" version uses the CauseWay DOS extender written by Michael Devore & John Wildsmith. It is linked directly into the official POV-Ray executible. If you are using an official version, this is the extender you will use. Although the CauseWay authors have graciously donated a copy to the POV-Team, CauseWay is still very much a commercial product. We cannot include it with the free source code for POV-Ray for you compile-it-yourself people. You will have to purchase it directly from the authors. Alternatly, another DOS extender called DOS4GW is supplied with the Watcom compiler. However it is limited to a total of 32meg of memory. If your version is designated "wat-d4g" it uses the DOS4GW extender. The instructions below explain how CauseWay and DOS4GW use memory. Do not try to use CauseWay variables with DOS4GW or vice-versa. Be sure to read POVMSDOS.DOC and run POVHELP to make sure you have all the remaining documentation. This file only applies to the Watcom compiled version. Also read POVWHERE.GET for more information on POV-Ray archives and support information. --------------------------------------------------------------------------- CAUSEWAY DOS EXTENDER CONFIGURATION Excerpted from Chapter 1 of the CauseWay DOS Extender User's Manual. It is (c) Copyright 1992-1996 by Michael Devore. Used by permission. Postal: Devore Software & Consulting PO Box 4283 Naperville, IL 60567-4283 USA CompuServe: 71540,62 Internet: 71540.62@compuserve.com Telephone: 1-708-717-6369 Fax: 1-708-717-6373 BBS: 1-708-717-9679 Note: The 708 area code changes to 630 in August of 1996. INTRODUCTION What is CauseWay for Watcom C++ and Assembly Language? CauseWay is a 386 DOS extender package for use with Watcom C++ and assembly language programs. It consists of a DOS extender, provided as a stub EXE for Watcom C++ applications. Within the standard DOS, and Windows and OS/2 DOS box environments, CauseWay supports very large memory models for applications on PC compatibles with an 80386SX processor or above without the need to use overlays or crude stopgap measures such as EMS/XMS swapping. To do this, the DOS extender runs applications in protected mode, rather than the real mode normally used in the DOS environments. CauseWay supports both 16-bit and 32-bit protected mode applications operating under a DOS environment. It makes full use of 386-level chip capabilities including demand paging of code and data, variable-sized segments up to 4G in length, mixing 16- and 32-bit segments as well as support for flat (non-segmented) memory addressing models. The CauseWay implementation of these powerful capabilities provides all their benefits while being transparent to the application user. Applications created using CauseWay are compatible with the VCPI and DPMI standards and run equally well on systems with no protected mode drivers or programs. CauseWay applications work with such diverse environments as normal DOS, DesqView, Windows 3.0 and above in both standard and enhanced modes, as well as DOS windows within OS/2 2.0 and above. CauseWay allocates memory from DPMI, VCPI, XMS, and INT 15H services, in addition to conventional DOS memory. This allows CauseWay applications to allocate memory through the CauseWay DOS extender without the need to detect or manipulate the various memory handling schemes. MINIMUM SYSTEM REQUIREMENTS CauseWay for Watcom C++ and Assembly Language requires a 386SX based computer or better. The required operating environment is MS- DOS or PC-DOS 3.1 or higher, Windows 3.0 or higher, OS/2 2.0 and above, or compatible operating system that provides a DPMI or VCPI DOS environment. DOS 3.3+ and a 386 machine or better are necessary to run CauseWay applications. CAUSEWAY MEMORY REQUIREMENTS The recommended minimum amount of total free physical memory for CauseWay applications is 500K total. 100-150K of this memory must be conventional DOS memory, the remainder may be extended memory. CauseWay applications can run in less memory, down to the 300K range, provided sufficient virtual (disk-based) memory is available, but application performance will decline significantly. More physical memory improves a program's performance, reducing virtual memory disk access overhead. When running the DOS-extended application, DOS first loads the CauseWay DOS extender in conventional memory. CauseWay establishes the protected mode environment, retrieves the application from the executable file - loading it first into extended memory, then conventional memory if extended is exhausted, then virtual (disk-based) memory if conventional is exhausted - sets up the application for execution, and finally passes control to the application to begin operation. No additional files are required to make your application run in 386 protected mode using the CauseWay DOS extender. OPERATIONAL CONSIDERATIONS WHEN USING CAUSEWAY The TEMP, TMP, and CAUSEWAY=SWAP environment variables are used by CauseWay to determine where to build its virtual memory swap file when an application is not operating under Windows or OS/2 (Windows and OS/2 use their own virtual memory files). Since CauseWay has integrated virtual memory, disk space is considered part of total memory. If you use the TEMP, TMP, or SWAP environment variable to point to a small RAM disk or almost full disk, free memory will be affected accordingly. If virtual (disk-based) memory is less than physical (installed on machine) memory, Cause Way turns off virtual memory. On the other hand, if you have a disk 300M free, CauseWay will have no problem reporting 300M free memory to your program, provided that virtual memory is not inhibited or limited by the CAUSEWAY environment variable memory settings. Memory operates differently under Windows and OS/2. With OS/2, the DPMI setting for the session determines available memory. With Windows, available memory is the total of physical memory plus the swap file size less any memory already in use by Windows or another Windows application. When creating a VMM swap file at application startup under DOS, CauseWay builds a list of possible paths in order of priority. CauseWay then works through the list until one of the entries provides both a valid drive and path specification and sufficient free space to begin operation. The first entry to succeed becomes the swap file drive with no further processing of the list. If CauseWay reaches the end of the list without finding a valid drive, it disables the virtual memory manager. The order of priority is: CAUSEWAY=SWAP, TEMP, TMP, and application execution path. If endusers reboot the system or turn off power while executing a CauseWay application under DOS, a temporary file will be left on the system by CauseWay. This will usually be a zero length file unless the application was large enough to exceed physical memory and CauseWay had started using its virtual memory manager. The temporary file name is requested using standard DOS functions, meaning the name will vary with different versions of DOS. It typically is a mixture of letters and numbers with no extension, although a .$$$ extension may be presented when operating under a network. Make sure you do not delete this temporary file while the CauseWay application is still active, as improper or erratic program operation, including lockups, may occur. Application startup times may increase significantly if free physical memory is less than the executable size. In such cases, not only must the executable be loaded into physical memory, but a virtual memory file of the executable file size must also be built. This file holds the portions of the executable that do not fit into physical memory and which have not been recently accessed. After startup is complete, the program will operate normally, paging to and from virtual memory as necessary. CauseWay automatically sets aside 32K of low DOS memory for allocation and use by developer routines via the GetMemDOS API function. The 32K memory block is available even if CauseWay needs to use virtual memory just to load an application. The set-aside amount can be increased by using the CAUSEWAY environment variable LOWMEM option although the additional set-aside goal is not guaranteed to be reached if too little conventional memory is left for CauseWay's operating requirements. ENVIRONMENT VARIABLES CauseWay can make use of three environment variables at runtime: TEMP, TMP, and CAUSEWAY. TEMP and TMP Environment Variables The TEMP and TMP environment variables specify the directory and drive where a swap file is built by CauseWay's virtual memory manager (VMM) when operating under DOS. Windows and OS/2 provide their own memory management functions which override CauseWay's use of the TEMP and TMP environment variables. The path indicated by TEMP will be used under DOS if both TEMP and TMP environment variables exist. Both settings are superseded by the CAUSEWAY=SWAP environment variable setting. SET TMP=C:\SWAP The example above directs the CauseWay DOS extender to create its swap file, if any, in the C:\SWAP directory. If no TEMP, TMP and CAUSEWAY=SWAP settings are present or are invalid, the current drive is used when creating a swap file. If free drive space is less than physical memory (extended and conventional) available at startup, then the DOS extender VMM is disabled, no swap file is created, and virtual memory is not available to the application. CAUSEWAY Environment Variable The CAUSEWAY environment variable controls operation of the DOS extender at application runtime. Seven options are supported, although they are ignored in a Window or OS/2 DPMI environment. Use any combination of the seven options in the following format: SET CAUSEWAY=[setting_1;] [setting 2;] [setting_n;] Items in brackets ([ ]) are optional. Do not actually type the brackets if you use the optional items. Items in italics should be replaced with actual values, separated by semicolons. Following is a description of the seven valid settings: DPMI Force DPMI rather than default VCPI usage whenever possible (recommended for 386^Max and BlueMax users). The memory manager must support DPMI or else this setting is ignored. EXTALL Force CauseWay to use all extended memory and sub- allocate memory from the bottom up instead of the default top-down approach. This setting is most useful for processor intensive enviromnents which have a small hardware CPU cache. Use of this setting means that no extended memory will be available for other programs while the application is loaded (including shelling to DOS). HIMEM:nnn Set maximum physical (conventional plus extended) memory that can be consumed by CauseWay. "nnn" is the decimal number of kilobytes that can be consumed. If memory allocation requests exceed this figure, CauseWay will use virtual memory, even if additional physical memory is present. If the HIMEM memory value exceeds available physical memory, then memory allocations operate normally. For example, HIMEM:2048 on a 4M machine would force virtual memory use after 2M of memory allocations (including loading the executable file). The remaining 2M of memory could be used by other applications while the CauseWay application is active. LOWMEM:nnn Set DOS (conventional) memory to restrict it from use by CauseWay. This memory is in addition to the default 32K low DOS memory block reserved by CauseWay for use by any applications which need to allocate DOS memory. nnn is the decimal number of kilobytes to reserve. If there is not enough conventional memory to satisfy the nnn request value then CauseWay will leave all conventional memory free that is not required by the extender to operate. Note that tnis option does not guarantee the amount of free DOS memory, just how much needs to be free before CauseWay will consume DOS memory after exhausting all extended memory. For example, LOWMEM:200 will attempt to reserve 200K of DOS memory, even if CauseWay has exhausted all extended memory and is using conventional memory to fill memory allocation requests. MAXMEM:nnn Set maximum linear address space provided by CauseWay. nnn is the decimal number of megabytes of linear address space. This setting is similar to HIMEM except that it includes any virtual memory. For example, MAXMEM:32 on a 16M memory system restricts VMM disk space usage to 32M, even if more disk space is present. MAXMEM:8 on the same system would restrict the application to 8M of memory (all physical). Note that the setting is in megabytes, rather than kilobytes used in the LOWMEM and HIMEM options. NOVM Disable all virtual memory use by CauseWay. If physical memory is exhausted, CauseWay will fail further memory allocation requests. SWAP:path Set CauseWay's virtual memory manager swap file path. This path takes precedence for choosing the location of a swap file over the TEMP and TMP environment variables. --------------------------------------------------------------------------- This concludes the information on the CauseWay DOS Extender which is linked into the official POV-Ray executible. The information below applies ONLY if you have compiled the program yourself using the Watcom compiler and the DOS4GW extender. --------------------------------------------------------------------------- --------------------------------------------------------------------------- DOS/4GW Configuration Guide WATCOM International Corporation Waterloo, Ontario, Canada This chapter explains how to use the DOS4G environment variable to suppress the banner that is displayed by DOS/4GW at startup. It also explains how to use the DOS16M environment variable to select the switch mode setting, if necessary, and to specify the range of extended memory in which DOS/4GW will operate. DOS/4GW is based on Rational Systems' DOS/16M 16-bit Protected-Mode support; hence the DOS16M environment variable name remains unchanged. 1.1 Suppressing the DOS/4GW Banner The banner that is displayed by DOS/4GW at startup can be suppressed by issuing the following command: set DOS4G=quiet Do not insert a space between DOS4G and the equal sign. A space to the right of the equal sign is optional. 1.2 Changing the Switch Mode Setting In almost all cases, DOS/4GW programs can detect the type of machine that is running and automatically choose an appropriate real- to protected-mode switch technique. For the few cases in which this default setting does not work we provide the DOS16M DOS environment variable, which overrides the default setting. Change the switch mode settings by issuing the following command: set DOS16M=value Do not insert a space between DOS16M and the equal sign. A space to the right of the equal sign is optional. The table below lists the machines and the settings you would use with them. Many settings have mnemonics, listed in the column "Alternate Name", that you can use instead of the number. Settings that you must set with the DOS16M variable have the notation req'd in the first column. Settings you may use are marked option, and settings that will automatically be set are marked auto. +------+---------------+-------+---------+-----------------------------------+ | | | |Alternate| | |Status|Machine |Setting|Name |Comment | +------+---------------+-------+---------+-----------------------------------+ |auto |386/486 w/ DPMI|0 |None |Set automatically if DPMI is active| |req'd |NEC 98-series |1 |9801 |Must be set for NEC 98-series | |auto |PS/2 |2 |None |Set automatically for PS/2 | |auto |386/486 |3 |386,80386|Set automatically for 386 or 486 | |auto |386 |INBOARD|None |386 with Intel Inboard | |req'd |Fujitsu FMR-70 |5 |None |Must be set for Fujitsu FMR-70 | |auto |386/486 w/ VCPI|11 |None |Set automatically if VCPI detected | |req'd |Hitachi B32 |14 |None |Must be set for Hitachi B32 | |req'd |OKI if800 |15 |None |Must be set for OKI if800 | |option|IBM PS/55 |16 |None |May be needed for some PS/55s | +------+---------------+-------+---------+-----------------------------------+ The following procedure shows you how to test the switch mode setting. 1. If you have one of the machines listed below, set the DOS16M environment variable to the value shown for that machine and specify a range of extended memory. For example, if your machine is an NEC 98-series, set DOS16M=1 @2M-4M. See the section, "Fine Control of Memory Usage" later in this chapter for more information about setting the memory range. +--------------------+---------+ | Machine | Setting | +--------------------+---------+ | NEC 98-series | 1 | | Fujitsu FMR-60,-70 | 5 | | Hitachi B32 | 14 | | OKI if800 | 15 | +--------------------+---------+ Before running DOS/4GW applications, check the switch mode setting by following this procedure: 2. Run PMINFO and note the switch setting reported on the last line of the display. (PMINFO, which reports on the protected-mode resources available to your programs, is described in more detail in the chapter, "Utilities".) If PMINFO runs, the setting is usable on your machine. 3. If you changed the switch setting, add the new setting to your AUTOEXEC.BAT file. Note: PMINFO will run successfully on 286 machines. If your DOS/4GW application does not run, and PMINFO does, check the CPU type reported on the first line of the display. You are authorized (and encouraged) to distribute PMINFO to your customers. You may also include a copy of this section in your documentation. 1.3 Fine Control of Memory Usage In addition to setting the switch mode as described above, the DOS16M environment variable enables you to specify which portion of extended memory DOS/4GW will use. The variable also allows you to instruct DOS/4GW to search for extra memory and use it if it is present. 1.3.1 Specifying a Range of Extended Memory Normally, you don't need to specify a range of memory with the DOS16M variable. You must use the variable, however, in the following cases: * You are running on a Fujitsu FMR-series, NEC 98-series, OKI if800-series or Hitachi B-series machine. * You have older programs that use extended memory but don't follow one of the standard disciplines. * You want to shell out of DOS/4GW to use another program that requires extended memory. If none of these conditions applies to you, you can skip this section. The general syntax is: set DOS16M= [switch_mode] [@start_address [- end_address]] [:size] In the syntax shown above, start_address, end_address and size represent numbers, expressed in decimal or in hexadecimal (hex requires a 0x prefix). The number may end with a K to indicate an address or size in kilobytes, or an M to indicate megabytes. If no suffix is given, the address or size is assumed to be in kilobytes. If both a size and a range are specified, the more restrictive interpretation is used. The most flexible strategy is to specify only a size. However, if you are running with other software that does not follow a convention for indicating its use of extended memory, and these other programs start before DOS/4GW, you will need to calculate the range of memory used by the other programs and specify a range for DOS/4GW programs to use. DOS/4GW ignores specifications (or parts of specifications) that conflict with other information about extended memory use. Below are some examples of memory usage control: set DOS16M= 1 @2m-4m Mode 1, for NEC 98-series machines, and use extended memory between 2.0 and 4.0MB. set DOS16M= :1M Use the last full megabyte of extended memory, or as much as available limited to 1MB. set DOS16M= @2m Use any extended memory available above 2MB. set DOS16M= @ 0 - 5m Use any available extended memory from 0.0 (really 1.0) to 5.0MB. set DOS16M= :0 Use no extended memory. As a default condition DOS/4GW applications take all extended memory that is not otherwise in use. Multiple DOS/4GW programs that execute simultaneously will share the reserved range of extended memory. Any non-DOS/4GW programs started while DOS/4GW programs are executing will find that extended memory above the start of the DOS/4GW range is unavailable, so they may not be able to run. This is very safe. There will be a conflict only if the other program does not check the BIOS configuration call (Interrupt 15H function 88H, get extended memory size). To create a private pool of extended memory for your DOS/4GW application, use the PRIVATXM program, described in the chapter, "Utilities". The default memory allocation strategy is to use extended memory if available, and overflow into DOS (low) memory. In a VCPI or DPMI environment, the start_address and end_address arguments are not meaningful. DOS/4GW memory under these protocols is not allocated according to specific addresses because VCPI and DPMI automatically prevent address conflicts between extended memory programs. You can specify a size for memory managed by VCPI or DPMI, but DOS/4GW will not necessarily allocate this memory from the highest available extended memory address, as it does for memory managed under other protocols. 1.3.2 Using Extra Memory Some machines contain extra non-extended, non-conventional memory just below 16MB. When DOS/4GW runs on a Compaq 386, it automatically uses this memory because the memory is allocated according to a certain protocol, which DOS/4GW follows. Other machines have no protocol for allocating this memory. To use the extra memory that may exist on these machines, set DOS16M with the + option. set DOS16M=+ Setting the + option causes DOS/4GW to search for memory in the range from FA0000 to FFFFFF and determine whether the memory is usable. DOS/4GW does this by writing into the extra memory and reading what it has written. In some cases, this memory is mapped for DOS or BIOS usage, or for other system uses. If DOS/4GW finds extra memory that is mapped this way, and is not marked read-only, it will write into that memory. This will cause a crash, but won't have any other effect on your system. 1.4 Setting Runtime Options The DOS16M environment variable sets certain runtime options for all DOS/4GW programs running on the same system. To set the environment variable, the syntax is: set DOS16M=[switch_mode_setting]^options. Note: Some command line editing TSRs, such as CED, use the caret (^) as a delimiter. If you want to set DOS16M using the syntax above while one of these TSRs is resident, modify the TSR to use a different delimiter. These are the options: 0x01 check A20 line -- This option forces DOS/4GW to wait until the A20 line is enabled before switching to protected mode. When DOS/4GW switches to real mode, this option suspends your program's execution until the A20 line is disabled, unless an XMS manager (such as HIMEM.SYS) is active. If an XMS manager is running, your program's execution is suspended until the A20 line is restored to the state it had when the CPU was last in real mode. Specify this option if you have a machine that runs DOS/4GW but is not truly AT-compatible. For more information on the A20 line, see the section, "Controlling Address Line A20" in this chapter. 0x02 prevent initialization of VCPI -- By default, DOS/4GW searches for a VCPI server and, if one is present, forces it on. This option is useful if your application does not use EMS explicitly, is not a resident program, and may be used with 386-based EMS simulator software. 0x04 directly pass down keyboard status calls -- When this option is set, status requests are passed down immediately and unconditionally. When disabled, pass-downs are limited so the 8042 auxiliary processor does not become overloaded by keyboard polling loops. 0x10 restore only changed interrupts -- Normally, when a DOS/4GW program terminates, all interrupts are restored to the values they had at the time of program startup. When you use this option, only the interrupts changed by the DOS/4GW program are restored. 0x20 set new memory to 00 -- When DOS/4GW allocates a new segment or increases the size of a segment, the memory is zeroed. This can help you find bugs having to do with uninitialized memory. You can also use it to provide a consistent working environment regardless of what programs were run earlier. This option only affects segment allocations or expansions that are made through the DOS/4GW kernel (with DOS function 48H or 4AH). This option does not affect memory allocated with a compiler's malloc function. 0x40 set new memory to FF -- When DOS/4GW allocates a new segment or increases the size of a segment, the memory is set to 0xFF bytes. This is helpful in making reproducible cases of bugs caused by using uninitialized memory. This option only affects segment allocations or expansions that are made through the DOS/4GW kernel (with DOS function 48H or 4AH). This option does not affect memory allocated with a compiler's malloc function. 0x80 new selector rotation -- When DOS/4GW allocates a new selector, it usually looks for the first available (unused) selector in numerical order starting with the highest selector used when the program was loaded. When this option is set, the new selector search begins after the last selector that was allocated. This causes new selectors to rotate through the range. Use this option to find references to stale selectors, i.e., segments that have been cancelled or freed. 1.5 Controlling Address Line 20 This section explains how DOS/4GW uses address line 20 (A20) and describes the related DOS16M environment variable settings. It is unlikely that you will need to use these settings. Because the 8086 and 8088 chips have a 20-bit address spaces, their highest addressable memory location is one byte below 1MB. If you specify an address at 1MB or over, which would require a twenty-first bit to set, the address wraps back to zero. Some parts of DOS depend on this wrap, so on the 286 and 386, the twenty-first address bit is disabled. To address extended memory, DOS/4GW enables the twenty-first address bit (the A20 line). The A20 line must be enabled for the CPU to run in protected mode, but it may be either enabled or disabled in real mode. By default, when DOS/4GW returns to real mode, it disables the A20 line. Some software depends on the line being enabled. DOS/4GW recognizes the most common software in this class, the XMS managers (such as HIMEM.SYS), and enables the A20 line when it returns to real mode if an XMS manager is present. For other software that requires the A20 line to be enabled, use the A20 option. The A20 option makes DOS/4GW restore the A20 line to the setting it had when DOS/4GW switched to protected mode. Set the environment variable as follows: set DOS16M= A20 To specify more than one option on the command line, separate the options with spaces. The DOS16M variable also lets you to specify the length of the delay between a DOS/4GW instruction to change the status of the A20 line and the next DOS/4GW operation. By default, this delay is 1 loop instruction when DOS/4GW is running on a 386 machine. In some cases, you may need to specify a longer delay for a machine that will run DOS/4GW but is not truly AT-compatible. To change the delay, set DOS16M to the desired number of loop instructions, preceded by a comma: set DOS16M=,loops 2.0 VMM The Virtual Memory Manager (VMM) uses a swap file on disk to augment RAM. With VMM you can use more memory than your machine actually has. When RAM is not sufficient, part of your program is swapped out to the disk file until it is needed again. The combination of the swap file and available RAM is the virtual memory. Your program can use VMM if you set the DOS environment variable, DOS4GVM, as follows. To set the DOS4GVM environment variable, use the format shown below. set DOS4GVM= [option[#value]] [option[#value]] A "#" is used with options that take values since the DOS command shell will not accept "=". If you set DOS4GVM equal to 1, the default parameters are used for all options. Example: C>set DOS4GVM=1 2.1 VMM Default Parameters VMM parameters control the options listed below. MINMEM The minimum amount of RAM managed by VMM. The default is 512KB. MAXMEM The maximum amount of RAM managed by VMM. The default is 4MB. SWAPMIN The minimum or initial size of the swap file. If this option is not used, the size of the swap file is based on VIRTUALSIZE (see below). SWAPINC The size by which the swap file grows. SWAPNAME The swap file name. The default name is "DOS4GVM.SWP". By default the file is in the root directory of the current drive. Specify the complete path name if you want to keep the swap file somewhere else. DELETESWAP Whether the swap file is deleted when your program exits. By default the file is not deleted. Program startup is quicker if the file is not deleted. VIRTUALSIZE The size of the virtual memory space. The default is 16MB. 2.2 Changing the Defaults You can change the defaults in two ways. 1. Specify different parameter values as arguments to the DOS4GVM environment variable, as shown in the example below. set DOS4GVM=deleteswap maxmem#8192 2. Create a configuration file with the filetype extension ".VMC", and call that as an argument to the DOS4GVM environment variable, as shown below. set DOS4GVM=@NEW4G.VMC 2.2.1 The .VMC File A ".VMC" file contains VMM parameters and settings as shown in the example below. Comments are permitted. Comments on lines by themselves are preceded by an exclamation point (!). Comments that follow option settings are preceded by white space. Do not insert blank lines: processing stops at the first blank line. !Sample .VMC file !This file shows the default parameter values. minmem = 512 At least 512K bytes of RAM is required. maxmem = 4096 Uses no more than 4MB of RAM virtualsize = 16384 Swap file plus allocated memory is 16MB !To delete the swap file automatically when the program exits, add !deleteswap !To store the swap file in a directory called SWAPFILE, add !swapname = c:\swapfile\dos4gvm.swp