AW: CGA card (Mitsubishi Electric) with 192K RAM?

Fred Cisin cisin at
Wed Sep 9 14:40:22 CDT 2020

>> Date and time of and any other DOS files will identify the 
>> version number.
On Wed, 9 Sep 2020, Jules Richardson via cctalk wrote:
> I've got 11/26/85 on

That would be MS-DOS version 3.10
Best known for having the "network redirector"? (which was also the 
loophole that permitted MSCDEX to have CD-ROM (bigger than 32MB, BUT DOS 
didn't know that it was local - thought that it was on a network 

1.00  August 1981
1.10  May 1982      double sided drives
1.25                MS-DOS
2.00  March 1983    HDDs, hierarchical directories, file handle API
2.10  October 1983  slowed down disk access for the PCJr Qumetrak 142
2.11                MS-DOS heavily customized by OEMs
3.00  August 1984   AT/5170, 1.2MB floppy, 
3.10  Nov 1985      network redirector?
3.20  January 1986  included PC-DOS 720K 3.5" floppy  (some OEM MS-DOS 
versions had 3.5" since MS-DOS 2.11)
3.30 April 1987   PS/2
3.31              MS-DOS heavily customized by OEMs, >32MB HDD
4.00              PC-DOS  HDD >32MB   "not compatible with Norton"
5.00 May 1991     DOS version in the displayed date
6.00 March 1993   massive inclusion of aftermarket add-ons
6.10              IBM's Version
6.20 October 1993 reliability improvements! (such as changing SMARTDRV) 
6.21              removal of infringing compression
6.22              addition of non-infringing compression

>> DIR /A  or
>> DIR /A:H
>> will let you see the hidden files (presumably IO.SYS and MSDOS.SYS; PC-DOS 
>> had IBMBIO.COM and IBMDOS.COM instead)
> The /a switch isn't part of the dir command in whatever 3.3 version I have.

sorry,  try ATTRIB *.*

> However, I just wrote a DOS 6.22 boot disk and that shows three hidden files 
> on the hard disk:
>  MSDOS.SYS (11/18/85)
>  MIO.SYS   (11/18/85)
> I'm guessing that the 'M' in MIO.SYS is "Mitsubishi" and the OS is tailored 
> in some way to the machine.
> TYPEing "sd.ini" indicates that it's related to Norton Speed Disk - not a 
> program I'm familiar with, but as that appears to be a defragmenter, it might 
> hint at why my drive isn't bootable and seems to be having problems with 
> various executables - I wonder if the directory structure "looks sane", but 
> file contents have been completely mangled.


Just like, . . .
when DOS 1.10/1.25 came out, there were disasters when people ran CHKDSK
1.0 on a 1.10 disk, even if running the CHKDSK on DOS 1.10.  Chkdsk 
proceeded to "FIX" the disk  (cf. Merck Veterinary manual)

THAT disaster resulted in later versions:
1) CHKDSK beagan to require "/F" ("fix"), AND requiring confirmation
before "repairs"
2) DOS utilities ("External commands") wouldn't run on any version of DOS
other than what they were bundled with.
THAT resulted eventuaally in release (V5.00?) of SETVER.
In my assembly language class, I showed them how to use DEBUG to patch
LINK and EXE2BIN to stop caring about DOS version, and assigned them to go
home and do it.   (comment out the conditional jump after Int21h, Fn 30h)

Ah, but another classic example, . . .
Norton fUtilities wasn't compatible with DOS 4.00 or 4.01 >32MB HDD.
It needed changes to comply with the 3.31 and newer changes to HDD
The press didn't phrase it that way!
They said, "DOS 4 is broken, it isn't compatible with Norton!  DOS needs 
to be fixed to work with Norton!"
Obviously, a new version of Norton fUtilities was called for to go with 
the new OS. 
MICROS~1 learned the hard way that major changes called for meeting with 
certain software vendors and giving them advanced warning, so that they 
could come out with new versions at same time as new OS release.

>> It is probably completely CGA compatible, unless you invoke of of its other 
>> modes.
> Maybe. Assuming that the hard drive's directory contents are intact, and 
> therefore there's nothing too unusual on the drive, I've perhaps got nothing 
> to lose by reformatting - the only issue is that MIO.SYS, how it differs from 
> Microsoft's, whether it's corrupt or not, and how - if it is intact - I can 
> migrate it over post-install.

If machine works OK from floppy 6.22 boot, then you could re-format with 
that.  Save a copy of the MSDOS.SYS, MIO.SYS, COMMAND.COM, and contents of 
DOS directory.

Try seeing what modes you can set with Int 10h, and poke memory in various 
modes.  You are going to be spending some time in DEBUG!

> Of course maybe speed disk (if that is even the cause of my problems) has 
> some kind of backup / undo aspect, but I doubt it.

Grumpy Ol' Fred     		cisin at

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