On 2018-04-25 16:39, Ronald Natalie wrote: > >> On Apr 24, 2018, at 9:27 PM, Dan Stromberg wrote: >> >> On Sun, Apr 22, 2018 at 2:51 PM, Dave Horsfall wrote: >>> 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. > Early pages were 1K. 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.) > 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 at softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol