release dates of early microcomputer operating systems, incl. Intel ISIS

Eric Smith spacewar at
Tue Sep 15 04:03:05 CDT 2015

On Tue, Sep 15, 2015 at 2:34 AM, Dave G4UGM <dave.g4ugm at> wrote:
> Looks like FLEX for the 6809 was also 1976...

A neat trick since the 6809 wasn't introduced until 1978. I assume
what is really meant is FLEX for the 6800.

> BUT I don't believe ISIS became an operating system until 1976 when ISIS II added support for disks....

Are you sure ISIS (one) didn't have disk support? I thought that was
shipped with the first Intel MDS-DOS floppy systems for use on the
MDS-800 in 1975.  A 1975 edition of the MDS-DOS Operator's Manual is
listed among other Intel manuals at:

> and the ISIS II manual has 1976 on Bitsavers has 1976 as the first  Copyright.....

Which doesn't tell us anything about ISIS (one).

> P.S. Often the search for "First" is fruitless,

Definitely.  I'm not necessarily looking for first, just early.

I found evidence of two operating systems for use on Intel's
development systems, sold by third parties along with their own floppy
disk systems, probably prior to Intel's MDS-DOS introduction.  MDOS by
Millenium Information Systems Inc. is mentioned in the April 1975
Microcomputer Digest, and DOS-80 by Applied Data Communications in the
May 1975 issue.  My vague recollection was that MDS-DOS was introduced
fairly late in 1975, but I don't have any definitive reference.

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