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Comparison of free memory for an old IBM PC/XT compatible system 
Saturday, August 7, 2021, 08:00 PM
Posted by Administrator
All big numbers are "Bytes". Nothing else loaded, no keyboard driver a.s.o.

MS-DOS 1.25 : 642784 english
MS-DOS 2.00 : 628688 english
MS-DOS 2.11 : 630784 english
MS-DOS 3.00 : 616720 english
MS-DOS 3.10 : 616800 english
MS-DOS 3.20 : 609984 english
MS-DOS 3.30 : 600368 english
MS-DOS 3.31 : 599488 english (Compaq DOS, first DOS for partitions > 32MB)
MS-DOS 4.01 : 589488 english
MS-DOS 5.00 : 593392 english, no HIMEM.SYS
MS-DOS 5.00 : 638592 english, with a 386, and with DEVICE=HIMEM.SYS and DOS=HIGH
MS-DOS 6.22 : 592384 english, no HIMEM.SYS
MS-DOS 6.22 : 638416 english, with a 386, and with DEVICE=HIMEM.SYS and DOS=HIGH

MS-DOS 4.01 : 589072 german version (just to see if a different language costs memory)

HIMEM.SYS 2.04 can be loaded on a 386 with MS-DOS 4.01, but there is no DOS=HIGH command, about 2.6KB less memory then (if loaded),
DOS 6.22 without hidden DRVSPACE.BIN file in root directory.

There are no further numbers for comparison of higher DOS versions, because it makes not really sense to load such a version on a very old 8088 PC compatible system.
Also, I do not wanted to compare the free memory numbers for 386 systems and above, with UMB usage you can probably get even more free memory than just with DOS=High.
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