IBM PC-DOS 2.10 explorations

Will Senn will.senn at
Sun Oct 4 09:52:49 CDT 2020

On 10/3/20 4:07 PM, Fred Cisin via cctalk wrote:
> On Sat, 3 Oct 2020, Will Senn via cctalk wrote:
>> 2. Most of the Assembly examples use DOS interrupt 21 for output. Is 
>> this typical of assembly programs of the time, or did folks use other 
>> methods?
> For simple stuff, Int21H works and is portable to anything running 
> Int10H is less portable.  Not as commonly used.
> If you need SPEED, which all commercial software perceived a need for, 
> then you need to determine WHERE video memory is (segment B000H for 
> MDA, segment B800H for CGA, with TEXT modes of EGA/VGA also using 
> those), and put bytes/words directly into video memory.  REP MOVSW was 
> generally the quickest way to put up a screenful of stuff (avoid 
> segment over-ride because REP MOVSW lost that if an interrupt occured 
> in mid transfer)
Great detail. I'll be playing around in the video memory. Int 21H is 
fine for printf style output, but I've never really played around with 
pages of data and this sounds like fun.

> Keyboard input could be done with Int21H, Int16h, or accessing memory 
> in the BIOS segment.
>> 3. I was able to find a lot of 5150/5160 and other manuals, but I 
>> couldn't find an IBM Macro Assembler 2.0 manual (there are plenty of 
>> IBM Macro Assembler/2 manuals, but those are for OS/2, not DOS). Does 
>> anyone know where I can find one online?
> MASM manual??!?
> MASM 5.0 was the first version to have documentation that a sane 
> person could say was adequate.
> The MASM 5.00 manualS were pretty usable for the earlier MASM.
Hmm. I'll give it a shot.

> I used Lafore as textbook for my assembly language class
>> 4. In y'all's view, what are the significant differences between IBM 
>> PC-DOS 2.10 and it's brother MS-DOS 2.x?
> 2.00 to 2.10 was minor changes.  Perhaps the most significant was that 
> the PCJr used the QumeTrak 142 (early half-height) drives, which were 
> TOO SLOW for 2.00, so PC-DOS 2.10 slowed down the DOS track to track 
> access time.
> 2.11 was MS-DOS ONLY, not PC-DOS.  It was one of the favorite ones for 
> OEMs to patch for different video or different drives (such as 720K 3.5")
> PC-DOS didn't get 3.5" drives until PC-DOS 3.20.
> PC-DOS 3.30 added 1.4M If you want CD-ROM, 3.10 added the "network 
> redirector".
> MS-DOS (NOT PC-DOS) 3.31, another favorite for patching, was the first 
> to support hard drives larger than 32M
> PC-DOS 4.00 was unpopular, partially becaause IBM didn't pre-warn 
> Norton to revise their fUtilities.
> MS-DOS 5.00 was the first to be sold RETAIL (not gray-market from an 
> OEM), and added such things as SETVER (so LINK and EXe2BIN didn't need 
> patching for DOS versions).
> MS-DOS 6.00 added a whole cartful of bundled aftermarket add-ons, 
> including compression, SMARTDRV disk cacheing, etc.
> PC-DOS 6.10 had a cartful of different aftermarket brands of the same 
> add-ons.
> MS-DOS 6.20 was the first version of MS-DOS for which imporving 
> reliability was primary goal!  (instead of adding smell-o-vision, 
> dancing kangaroos and yodelling jellyfish)
> It backed off the settings for SMARTDRV so that disks didn't get 
> trashed (incorrectly blamed on compression)
> 6.21 was same, without compression due to copyright lawsuit(s).
> 6.22 was same with non-infringing compression

Great detail, thanks.

>> 5. I'm thinking of moving on to 3.3 at some point, in your view, what 
>> are the advantages?
> Consider 3.31, instead of 3.30, to get larger drive support.
I am using a Thinkpad T430 w/DOS 6.22. If I can figure out how to get 
3.31 on there, I'll give it a shot. I bought a Floppy-USB connector for 
my old 1.44 floppy drive and it works fine with DOS 6.22, but I'm not 
sure where to locate 3.31 media that I could burn onto a 1.44 floppy and 
boot. I have sealed IBM DOS 3.3 media, but I don't think my T430 is 
really compatible :). So, I'm not keen on opening the seal...

> Bob Wallace (MICROS~1 10th? employee) wrote the IBM PASCAL.  He 
> advised me to NOT use the run-time library.
Well, there's a thought. I have Turbo Pascal 3 and it works fine. I just 
like the feeling of running the old stuff.

> -- 
> Grumpy Ol' Fred             cisin at

Thanks Fred!

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