Re: ancient OS history, ARM is sort of channeling the IBM 360

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.