Happy Birthday VAX 11/780 (influence of)

On 2010-10-29 19:00, "Chuck Guzis"<cclist at sydex.com> wrote: I think that virtual address space is intimately connected to virtual memory, and you cannot have one without the other. If your program vrites data to address 0, and reads it back, and get the same data back, and another program on the same machine, at roughly the same time, write to address 0, and reads the same data back, and that data is different than the first programs data, then I'd say you have virtual memory. Certainly. If we just disregard that the code needed to implement this thing might need more memory than 8K. The program that we intend to fool must have atleast 8K of physical memory, to which we can read in and out pages. With 16K that would leave just 8K for out demand paging software... Well, actually, this is a bit too simplified. An instruction can potentially refer to 4 pages, so we would need to be able to have four pages to be able to fully fool a program. That would mean minimum 32K of physical memory to use for the user program. And then some for your kernel. But you'd probably be able to come in under 56K, while fooling the program that is has 64K. With less than four pages, you could get into a situation where mapping in one page means you have to map out another, which the instruction refers to, and when you restart the program you'll just get another page fault, ad infinitum... :-) 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