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From: John Levine <johnl@taugh.com>
Newsgroups: comp.arch
Subject: Re: interative use, The Design of Design
Date: Wed, 8 May 2024 21:02:41 -0000 (UTC)
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According to Stephen Fuld  <sfuld@alumni.cmu.edu.invalid>:
>> With sufficiently disciplined programming, you could swap and move data
>> by updating the base registers.  APL\360 did this quite successfully
>> and handled a lot of interactive users on a 360/50.
>
>Wasn't APL\360 an interpreter?  If so, then moving instructions and data 
>around was considerably simpler.

That's right.  It could switch between users at well defined points that
made it practical to update the base registers pointing to the user's workspace.

>> Reading between the lines in the IBMSJ architecture paper, I get the
>> impression they believed that moving code and data with base registers
>> would be a lot easier than it was, and missed the facts that a lot of
>> pointers are stored in memory, and it is hard to know what registers
>> are being used as base registers when.
>
>Interesting.  That would seem to imply that it wasn't that they didn't 
>think about the problems that base addressing would cause, they just 
>(vastly) underestimated the cost of fixing it.  A different "design" 
>problem indeed.

In Design of Design, Brooks said they knew about virtual memory but thought
it was too expensive, which he also says was a mistake, soon fixed in S/370.

-- 
Regards,
John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly