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15.1 How much virtual memory do you have?

Q: How much virtual memory can I use in DJGPP programs?


A: That depends on the DPMI host you are using. CWSDPMI (the free DPMI host which comes with DJGPP) will let you use all available conventional and extended memory (up to 256MB) and up to 256MB of disk space, for a grand total of 512MB of virtual memory for your application. Try a malloc(50*1024*1024) some day.

With other DPMI hosts, your mileage may vary. Quarterdeck's QDPMI, for instance, has a bug in some of its versions which effectively disables virtual memory under DJGPP (described in QDPMI VM bug, below), so you only have whatever free physical RAM is left. Under Windows 3.X, the amount of virtual memory you get depends on various virtual memory settings in the Control Panel and on the .pif file settings for the program you run (see Windows allocation subtleties, below). Under Windows 9X, the memory settings of the DOS Box Property Sheets define how much virtual memory a DJGPP program will get (see Windows 9X allocation details, below). OS/2 reportedly can be configured to support up to 512MB of DPMI memory.


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