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DOS Memory Management

108 points by ingve

by 5o1ecist

6 subcomments

I remember UMB. I remember that, as a teenager, I was obsessed with figuring out how to squeeze the most free conventional memory out of MS-DOS 6+ ... or 7+? I was stuck at around 615k, maybe 620ish. It annoyed me greatly, because I knew there was still headroom left.
The thing was, that upper memory wasn't just for TSRs. Anything one can shove there, would happily stay there and run just fine.
My journey towards the most free, conventional memory ended at 637k on my 386 DX-33 with 8megs of RAM and a SoundBlaster card, with everything possible being shoved to high memory. Mouse driver, MSCDEX and even COMMAND.COM.
637k. So proud, much wow!
Good times!

by markus_zhang

0 subcomment

I have to admit, DOS memory management is very fascinating to me as a very amateur kernel investigator. I have a book called “DOS beyond 640k” which describes all sorts of extensions people back in the 80s invented to get as much free memory as possible. The contents of course are irrelevant nowadays, but it is still interesting to read as a tech book.

by GarnetFloride

0 subcomment

I set up a computer for an engineering department. It was an IBM PS/2. They wanted to run AutoCAD and Ventura Publisher, one used extended memory and the other expanded.
I ended up making batch files that swapped around autoexec.bat and config.sys files so they could run.

by throw0101c

0 subcomment

No discussion on the topic would be complete without QEMM:
* https://en.wikipedia.org/wiki/QEMM

by gschizas

2 subcomments

'MZ' has been confirmed to be the initials of Mark Zbikowski, there's no question about it. It's not "Memory" + "Last".

by sqldba

0 subcomment

There's a retail tool that lets you get a lot more memory below 1MB. 639K (625K free) conventional, 262K upper (177K free).
If you remember seeing how, you'll get a free virtual cookie.

by nnevatie

0 subcomment

Good times. Our DOS game PaybackTime 2 was only capable of using conventional memory. That was a major reason for the game really not having any proper animations for its player characters.

by esafak

0 subcomment

Lacking a discussion on protected mode; the means to access the 1MB+ area (up to 16MB in 286, and 4GB in 386 and later).
https://en.wikipedia.org/wiki/DOS_Protected_Mode_Interface https://en.wikipedia.org/wiki/Virtual_Control_Program_Interf...
I remember toying with DPMI in assembler.

by ubermonkey

0 subcomment

Mmmm, flashbacks of complex sets of AUTOEXEC.BAT & CONFIG.SYS files that we'd swap in and out using batch files to support different memory configurations...

by mlvljr

0 subcomment