DJGPP FAQ -- How to get the most RAM for DJGPP programs?

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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?

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: most of them 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.
If you are using QEMM (version 8.0 or later), you must include the USERAM=128M parameter (here for 128MB of installed memory) 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 r4 of CWSDPMI. Previous versions only supported up to 128MB of main memory, and had bugs with more than 64MB.

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, try to convince Charles Sandmann to upgrade CWSDPMI. However, note that breaking the current limit of 256MB will make CWSDPMI considerably slower (it requires to abandon 16-bit arithmetics and move to 32-bit longs, which causes Turbo C, the compiler used to build CWSDPMI, to generate much slower code). Charles says that people who got such customized versions of CWSDPMI were never really happy with its performance, so he advises to consider the 256MB limit a serious reason to switch to another operating system. For example, a dual-boot DOS/Linux system will probably do. 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).

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