3.10 How to get the most RAM for DJGPP programs?

Q: How do I set my system so that DJGPP programs could use all of my 256MB of installed physical RAM?

Q: I have 128MB of memory installed, but go32-v2 only reports 32MB, how can I get more?

Q: You say that CWSDPMI supports up to 512MB of total virtual memory, but I cannot get more than 128MB!

A: You can have as much as 256MB of physical memory in DJGPP programs, provided that you have at least that much installed, and that you observe the following guidelines:

• Use CWSDPMI as your DPMI server. With a possible exception of Qualitas' 386Max, all the other DPMI servers usually cannot support more than 64MB. (The DPMI server built into Windows usually won't even let you have more than 64MB physical and virtual memory combined, unless you have more than 64MB installed physically, see below.)
• Do not install any memory managers but HIMEM: most of the others will limit the amount of accessible memory to 64MB (EMM386 usually limits it to 32MB unless you turn off the VCPI support using the NOVCPI NOEMS parameters on the EMM386 command line). Using HIMEM from MS-DOS 7 does allow access to more than 64MB. Note that you must install HIMEM, since without it, BIOS is the only way to find out how much memory is installed, and the standard system BIOS only supports up to 64MB of memory.
• If you are using QEMM (version 8.0 or later), you must include the USERAM= parameter (e.g., USERAM=128M for 128MB) on its command line in your CONFIG.SYS and specify the exact amount of memory installed on your machine, otherwise QEMM won't support more than 64MB.
• Make sure you use the latest release r5 of CWSDPMI. Versions before r4 only supported up to 128MB of main memory, and had bugs with more than 64MB. CWSDPMI r4 supports up to 256MB of memory, but has bugs when the total amount of memory approaches 256MB, so if you use r4, make sure the total amount of memory is less than 256MB.
• If you want to use more than 128MB of virtual memory, run the CWSPARAM program and enlarge the "Maximum number of 4K pages in swap file" parameter. The default value is for 128MB of virtual memory.

Another possibility is to run your program from the Windows 9X DOS box, after changing the EMM386 line in your CONFIG.SYS like this:

 DEVICE=C:\WINDOWS\EMM386.EXE NOEMS L=131072

I'm told that this line (here for 128MB of installed memory) together with an "Auto" setting of the DPMI memory for the DOS box allows DJGPP programs to use up to 117MB of memory when running from the DOS box under Windows 9X.

If you need to use more than 256MB of physical memory, upgrade to CWSDPMI r5 or later. Another possibility is to run under OS/2 which features a built-in DPMI 1.0 support which can be configured to support as much as 512MB of DPMI memory (the user who reported this didn't know how much of this can be physical RAM).