Re: base and bounds, Why I've Dropped In

According to Thomas Koenig  <tkoenig@netcologne.de>:

The problem of the /360 was that they put their base registers in
user space.  The other machines made it invisible from user space
and added its contents to every memory access.  This does not take
up opcode space and allows swapping in and out of the whole process,
which was a much better solution for the early 1960s. (Actually, I
believe the UNIVAC had two, one for program and one for data).

The PDP-6, which was designed around the same time as the 360, had
base and bounds relocation registers which indeed allowed swapping.
The follow-on KA10 had two, the low half of the address space for
private data and the high half for shared code. Later PDP-10s all had
paging.

Base and bounds is OK, but I gather that the PDP-6 and KA10 spent
a lot of time shuffling memory to consolidate free space.  An
underappreciated advantage of paging is that you don't have to do
that, since one page frame is as good as another.

(Yeah, I know some sysems have big pages and small pages but those
don't seem very popular. And some systems don't run I/O through a page
map so you have to coonsolidate space for large I/O operations.)
--
Regards,
John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies",
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