According to Peter Flass <
peter_flass@yahoo.com>:
But note that the trend of falling memory prices was already becoming
clear by the 1970s, if not earlier. The earliest batch systems only kept >>> one program in memory at one time, and swapped it out for another one when >>> it went into any kind of I/O wait, to keep the CPU busy...
They did no such thing.
Well, early timesharing systems such as PDP-11 systems or TSO.
Timesharing systems all swapped because programs spent most of their
time waiting for people at terminals. That meant delays of at least
seconds so it made sense to spend a fraction of a second swapping to
disk.
Genrally speaking, batch systems only waited for tapes and disks. Swapping wouldn't make sense because the swap disk would be no faster than the
device a program was waiting for. Indeed it might be the same device.
Starting in the 1960s there were plenty of batch systems that ran multiple programs, switching back and forth when the programs were I/O bound, but the programs were all in memory so it was just context switching, no extra I/O. Once
virtual memory and paging arrived, we can argue about whether the I/O for paging
was like swapping, although it is my strong impression that if a system's memory
was so overcommitted that it did a lot of paging, it was unlikely to get much useful work done.
--
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
--- MBSE BBS v1.0.8.4 (Linux-x86_64)
* Origin: Taughannock Networks (3:633/280.2@fidonet)