[geeks] Oldest OS Still Developed

[Geoffrey S. Mendelson]

On Wed, Oct 18, 2006 at 10:06:21PM +0100, Mike Meredith wrote:
> The funniest thing about IBMs mainframe operating systems is the story
> of VM. IBM repeatedly tried to kill it off and get customers to use
> their 'real' OS, and found it impossible ... especially when their own
> internal developers were busily using it to develop that 'real' OS!

IBM had two main timesharing operating systems at the time. One was
TSO a part of MVS and the other was VM. VM was the more popular (BTW, it
was distributed in source code). TSO was used by systems programmers.

When IBM dropped VM, they found that their VM customers were not migrating
to TSO, they were looking at DEC's offerings. So IBM reversed their
decision and kept VM. They also took a bunch of public domain enhancments
to VM and sold them as VM/SP (VM/370 System Product). This was the first
of the non free operating system offerings, spreading to DOS as DOS/VSE and
MVS as MVS/SP. 

The major enhancments of DOS/VSE were support for more effecient use of multiple
DOS vitrual machines under VP/SP.

The same thing happened to DEC years later. When they decided to drop UNIX 
to force their users into runing VMS, customers started making plans
to drop DEC entirely and convert their VMS useage to UNIX.

Unlike IBM, DEC never did recover, although they reinstated UNIX. 

Geoff.
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