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I 100% disagree with this answer. If "virtual memory" referred to paging, then a system that doesn't page (say, one with no swap or page files enabled) could not support virtual memory. But that's obviously insane.
– David Schwartz
Commented Aug 28, 2011 at 22:09
@DavidSchwartz - I initially had a reaction similar to yours, but in reading the answer in more detail, I don't think it is so bad. Consider Wikipedia/virtual memory/Paged says "Nearly all implementations of virtual memory divide a virtual address space into pages, blocks of contiguous virtual memory addresses". That is, "paging", in the broad sense, does not require a page file, but refers to the mapping of virtual addresses into physical addresses.
– ToolmakerSteve
Commented May 14, 2017 at 10:42
1

Hmm, on the other hand, Lee says "All of the pages of information don't fit in memory, so some pages are put on disk, and loaded again later.", so David is right: this answer misses the essential fact that paging is not just about paging to disk. On the plus side, Lee does go on to mention other benefits of virtual memory (memory isolation). If this answer were reworded to not muddle "mapping pages of virtual memory" with "paging to disk", it would be more useful.
– ToolmakerSteve
Commented May 14, 2017 at 10:51
@ToolmakerSteve The problem is that this is a very common misconception and anything that strengthens that misconception is, IMO, a bad thing. It's especially bad here when this answer is trying to explain the very basic concepts in a very simple matter -- there it's the most important not to lay a groundwork based on a common misconception!
– David Schwartz
Commented May 14, 2017 at 17:35
@DavidSchwartz - I agree. You are right, he is not defining "virtual memory", he is defining "how a page file works". At first I had thought that the problem was merely that Lee failed to distinguish between "paging = mapping pages of memory from virtual to physical" versus "page file = mapping pages to disk", but after re-reading, he really was talking only about mapping to disk. (As we can see, from the textbook quote, from all the other answers except the Captain's, and from a google search, this commingling of the two concepts is very widespread. I'm sure I've been guilty of it.)
– ToolmakerSteve
Commented May 19, 2017 at 9:45

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