[rescue] More IBM emulation fun

Mike Meredith very at zonky.org
Tue Feb 10 01:57:14 CST 2009

On Mon, 09 Feb 2009 23:08:00 -0700, Scott M wrote:
> On Mon, 9 Feb 2009 20:04:36 -0600, Bill Bradford wrote:
> > ... VM/370 ... documentation ... 
> http://www.bitsavers.org/pdf/ibm/370/vm370/
> At this URL, this doc:  Introduction_To_VM370_Course_Jul75.pdf
> has this chapter heading:  "VIRTUAL MACHINE DESCRIPTION". 
> Virtualization in 1975?  Really? 

Try 1965. VM/CMS derives from CP/CMS.

> However with so little memory available, it seems strange that 

Actually it sounds like a lot to me. Ok, I'm not quite that old but you
can do quite a bit in 256K if you don't have any graphical interfaces to
worry about. 

> Maybe DOS/360 and CMS were single-user and virtualization was a way 

(In the case of DOS) Not just single-user, but also single-tasking.
There was a great deal of opposition to the idea of interactive
computing (timesharing) in the commercial sector at the time.

CMS was also single-user, but that was intentional as CP/CMS was a
(relatively) quick hack to produce a workable timesharing system as TSS
was in trouble. The concept of virtual machines was sufficiently
powerful that CP spread like a virus through IBM whilst IBM management
was trying to kill it off.

As my dad later pointed out, it's kind of handy having a mainframe of
your own when you're writing o/s code. Even if it's "only" a virtual

Mike Meredith (http://zonky.org/)
 Men never do evil so completely and cheerfully as when they do it from
 religeous conviction
  -- Blaise Pascal

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