Re: transactions vs interactive, was The Design of Design

According to Tim Rentsch  <tr.17687@z991.linuxsc.com>:

Another (and perhaps larger?) part of the motivation was about the
relative priorities, and this was (I believe) a conscious element.
In particular, interactive use was thought to be important for
program development (Brooks says something along these lines in
TDOD).  I conjecture that IBM consciously decided -- whether
rightly or wrongly -- that program development was only a small
fraction of what IBM's market wanted to do with their computers,
and so IBM didn't prioritize it;  they thought that what little
program development was needed could be carried out adequately
under the batch processing model. That 's understandable -

It's the Jevons Paradox. If you improve your processes to use
something more efficiently, you often end up using more of it because
the overall usage increases. Jevons said it about coal and steam
engines but it happens all the time.

IBM was certainly familiar with time-sharing from Project Mac which
ran on a 7090. Time-sharing needs system managed context switches
which are expensive, as opposed to SAGE/SABRE style transaction
processing where each bit of application code manages its own context.
In practice it also needs dynamic address translation which they added
to the 360/67 to bid on the Multics project, and to all 370s both for
that reason and the horrible OS memory management Lynn has described.

Among the many differences between IBM and DEC computers was that
IBM's had channels which did a lot of work between relatively
infrequent interrupts, while DEC's did not often had interrupts for
each word of data. (They did have DMA which they called data break but
only for fast devices like disks, not terminals or medium speed
DECtapes.)

At the time IBM's choice made sense. Now of course everything is so
much faster that the mini-server on my desk that is about the size of
an orange has an ATA disc controller that does more than a 1960s
channel, and the CPU takes thousands of interrupts per second
without noticably slowing down.

PS:

A quote from Tom Watson Sr comes
to mind (paraphrased):  "I think there's a world market for about
five computers."

He never said that. What he probably said in 1943 was more like five
computers could do all the computing the world is doing, which was
true. I would think he was quite aware that as costs came down the
demand would go up but I think everyone was surprised at how fast that
happened.
--
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