Hi there, I've did a quick test of a few not so popular DOSes and their memory consumption.

Here's my little list so far (640KB DOS memory, not start-up files) :

Wendin Multiuser DOS 2.11 [185856 Bytes free]
PC-MOS 386 3 [418960 Bytes free; reported by CHKM]
PC-MOS 386 2.20 [445600 Bytes free; reported by CHKM]
PC-MOS 386 1.02 [470992 Bytes free; reported by CHKM]
(note: multi-tasking/multi-user OSes can take advantage of the 80386 MMU to provide more DOS memory)

sisne plus [551,680 Bytes free]
Datalight DOS 7.1 [558,272 Bytes free]
DOS Plus 1.2 [565,488 Bytes free; reported by CHKM/PC-MODE]
X-DOS 5 [568,128 Bytes free]
Sigma Four DOS 1.0 [581,408 Bytes free]
TRDOS 8086 1.0.x [585,728 Bytes free]
DR DOS 5 [586,640 Bytes free]
DR DOS 6 [588,064 Bytes free]
DeviceLogics DR-DOS 8 [598,944 Bytes free]
DCP 3.30 [599,392 Bytes free]
AlphaDOS 3.30 [601,376 Bytes free; reported by CHKM]
PTS 6.42 GER [601,744 Bytes free]
NOVELL DOS 7 [606,224 Bytes free]
Janus 2.0 [610,800 Bytes free]

MS-DOS 2.11 [623792 Bytes free; reported by CHKM]

For comparison, here's vwestlife's list from Vintage Computer Federation forums :

I just went through all my boot disks, and ran CHKDSK on each one to display the amount of free RAM (out of 640K) on each one, u […]
Show full quote

I just went through all my boot disks, and ran CHKDSK on each one to display the amount of free RAM (out of 640K) on each one, using a totally clean boot (no CONFIG.SYS or AUTOEXEC.BAT):

PC DOS 2.00 ... 630,672 bytes
PC DOS 2.10 ... 630,672
PC DOS 3.10 ... 616,432
MS-DOS 3.10 ... 616,432
PC DOS 3.21 ... 609,392
PC DOS 3.30 ... 600,528
MS-DOS 3.30 ... 600,368
IBM DOS 5.00 ... 593,328
MS-DOS 5.00 ... 593,328
MS-DOS 6.00 ... 592,256
IBM DOS 6.10 ... 593,056
MS-DOS 6.22 ... 592,256
PC DOS 6.30 ... 593,024
PC DOS 7.00 Revision 0 ... 593,840
PC DOS 2000 (7.00 Revision 1) ... 593,760

I also have an MS-DOS 4.01 boot disk, but not a copy of CHKDSK which will work with it, so I can't give it an accurate free RAM amount, but judging by what other utilities report, it's somewhere in the ballpark of 590,000 bytes. So IBM claimed that PC DOS 7 offered the most free RAM of any version of DOS since 3.3, and that does appear to be true!

Source: https://forum.vcfed.org/index.php?threads/rec … 95/#post-540236

This is just a silly little thread here that I may update from time to time. 😅
Knowing conventional memory usage might be useful to PC/XT users..

Best wishes,
Jo22