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From: Lawrence D'Oliveiro <ldo@nz.invalid>
Newsgroups: comp.arch
Subject: Re: ancient OS history, ARM is sort of channeling the IBM 360
Date: Sun, 30 Jun 2024 07:22:23 -0000 (UTC)
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On Sun, 30 Jun 2024 04:33:11 -0000 (UTC), Stephen Fuld wrote:

> Lawrence D'Oliveiro wrote:
> 
>> By the 1970s, CPU/RAM speeds had improved to the
>> point where copying records a few hundred bytes at a time between
>> buffers was not the performance bottleneck; disk I/O was.
> 
> Yes, but given multiprogramming, even in the 1970s, you would typically
> have several batch programs running at the same time, so during waits
> for I/O, another program could use the CPU.  But using the CPU to move
> records meant it couldn't be doing anything else at the same time.

Scraping the bottom of the barrel, much?

Work out the numbers. The CPU time necessary to copy a single record is 
most likely a small fraction of the time it takes to service an I/O 
interrupt.

And this is not taking into account the fact that I/O interrupts run at a 
higher priority than user-level tasks like copying buffers, anyway.