25 Apr
2018
25 Apr
'18
11:43 p.m.
On 2018-04-25 16:39, Ronald Natalie<ron(a)ronnatalie.com> wrote:
What machines are we talking about then?
PDP-11 have 8K pages. VAX have 512 byte pages, if we talk about hardware.
(And yes, I know pages on PDP-11s are not fixed in size, but if you want
the page to go right up to the next page, it's 8K.)
On Apr 24, 2018, at 9:27 PM, Dan
Stromberg<drsalists(a)gmail.com> wrote:
On Sun, Apr 22, 2018 at 2:51 PM, Dave Horsfall<dave(a)horsfall.org> wrote:
Early
pages were 1K. Now, how many youngsters know the difference
between paging and swapping?
I'm a mere 52, but I believe paging is preferred
over swapping.
Swapping is an entire process at a time.
Paging is just a page of memory at a time - like 4K or something thereabout. The fun argument is what is Virtual Memory.
Typically, people align that with paging but you can stretch the definition to cover
paging.
This was a point of contention in the early VAX Unix days as the ATT (System III, even
V?) didn’t support paging on the VAX where as BSD did.
Our comment was that “It ain’t VIRTUAL memory if it isn’t all there” as opposed to
virtual addressing.
Weird comment. What does that mean? On a PDP-11, all your virtual memory
was always there when the process was on the CPU, but it might not be
there at other times. Just as not all processes memory would be in
physical memory all the time, since that often would require more
physical memory than you had.
But you normally did not have demand paging, since that was not really
gaining you much on a PDP-11. On the other hand, overlays do the same
thing for you, but in userspace.
So you would claim that ATT Unix did not have virtual memory because it
didn't do demand paging?
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt(a)softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
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