Available Conventional Memory for MS-DOS (82714)

SUMMARY

Running under a system that has very little loaded into conventional memory (a "bare-bones" system), the Microsoft Windows operating system versions 3.1 and 3.0 operating in enhanced mode will reduce the amount of memory available to MS-DOS programs by 4K to 16K.

MORE INFORMATION

A combination of the following can force Windows in enhanced mode to use more conventional memory:

Memory for an MS-DOS virtual machine (VM) must start at a 4K page boundary (because of the paging mechanism that the 80386 processor uses.) In the worst case, this can cause slightly more than 3K of memory address space to go unused.
Some machines have an additional data area used by the machine's system ROM BIOS called the EBIOS data area. This data area usually resides at the top of the conventional memory (near the 640K boundary). Because the 80386 paging mechanism deals with 4K pages of memory, the EBIOS data area occupies 4K of space in Windows in enhanced mode. (Normally, when Windows is not being run, the EBIOS area takes up only about 1K of memory because there is no limitation of 4K-sized memory pages.)
When an MS-DOS prompt is started from within Windows, a second copy of the MS-DOS command interpreter, COMMAND.COM, is being started. This can account for an additional memory loss of 4K.