 |
 |
> I see the problem. You have the definition of virtual memory wrong. > Virtual memory is strictly a software concept, and has nothing to > do with physical memory, which generally consists of RAM + swap. I belive that YOU have the definition of virtual memory wrong. > To quote from Tanenbaum, "Modern Operating Systems": > The basic idea behind virtual memory is that the > combined size of the program, data and stack may exceed > the amount of physical memory available for it. In this case, Tanenbaum uses the term "physical memory" to refer to RAM, not RAM+swap. This is obvious, because no process can have the combined sizes of it's program, data, and stack exceed RAM+swap. In fact, the combined sizes of ALL RUNNING PROCESSES must be less than RAM+swap. Tanenbaum's sentence does not define virtual memory, but only gives "the basic idea behind" it. Now, the 5th edition of Doctor Linux, Part XIII, 7.1 Making Virtual Memory, says: "To create an additional 8 megs of virtual memory..." and then shows how to make a swap file. The 8 megs of swap space is the virtual memory. Virtual memory is NOT the 4 gigs of "addressable memory." One can fragment the 4 gigs of addressable memory, but that would take a lot of work. The OS will move data in RAM and swap (a.k.a. "virtual memory"), as needed. So if two megs of RAM+swap are available, but only in 512k blocks, and a process tries to allocate another meg, the OS can move the data around in RAM+swap to make a contiguous 1 meg block. That is why we programmers don't have to worry about fragmenting memory, until we reach the 4 gig limit. The OS writers have already solved the problem. > If you still disagree, I suggest we take the discussion off-line. Only if _I_ get the last word _online_. :-) -jack %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%