[rescue] More IBM emulation fun

Scott M scott.mickey.sunhelp at atsgate.com
Tue Feb 10 00:08:00 CST 2009

On Mon, 9 Feb 2009 20:04:36 -0600, Bill Bradford wrote:
> ... VM/370 ... documentation ... 

At this URL, this doc:  Introduction_To_VM370_Course_Jul75.pdf
has this chapter heading:  "VIRTUAL MACHINE DESCRIPTION". 
Virtualization in 1975?  Really? 
I guess I should not have been surprised, since the "VM" in VM370 
stands for "Virtual Machine".  
However with so little memory available, it seems strange that 
anyone would want to put more than one OS on a machine of that era. 
Page 8 of this doc shows a "256K DOS BATCH" virtual machine running 
on a S/370 Model 145 along with five "320K CMS" virtual machines. 
But DOS didn't exist in 1975!   -Turns out this isn't MS-DOS, but 
IBM DOS/360 or some variant of it: 
Maybe DOS/360 and CMS were single-user and virtualization was a way 
to make the machine multi-user?  Or maybe IBM had the same problems 
as today where code needs to be isolated because it tries to write 
to memory that belongs to someone else? 
-Scott M

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