This crash course in Unix should give you a first helping of guidance—enough to perform some genuinely useful tasks in Mac OS X, and to acquire a feeling for how Unix commands work.
Power Users’ Clinic: Secrets of Virtual Memory
The top command’s table offers a fascinating look at the way Mac OS X manages memory. In the “VM” section, for example, you’ll see current statistics for pageins and pageouts—that is, how many times the virtual-memory system has had to “set down” software code for a moment as it juggles your open programs in actual memory. (These numbers are pointed out in Figure 17-3.)
The pageins and pageouts statistics are composed of two different numbers, like this: 45451(0) pageins, 42946(0) pageouts. The big number tells you how many times your Mac has had to shuffle data in and out of memory since the Mac started up. The number in parentheses indicates how much of this shuffling it’s done within the last second.
This is the number to worry about. If it stays above zero for a while, your Mac is gasping for RAM (as the hard drive thrashing sounds and program-switching delays are probably also telling you).
In the listing of individual programs, the last four columns provide details about the memory usage of each listed program. The one you care about is the RPRVT (Resident Private) column, which shows how much memory each program is actually using at the moment. (If you remember the About This Macintosh memory graph of Mac OS 9, then you probably remember ...
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