Don't understand RAM in OS X

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Help me understand how this works. In the Activity Monitor, I've got: Wired, Active, Inactive, Used, and Free. What the..?? So, as I understand it:

Wired: RAM that is actively in use
Active: Uh... RAM that is actively in use.. ??
Inactive: RAM not being used but is for some reason tied up.. will be used as soon as it is needed (this is like Linux, how it eats up as much RAM as possible and gives it out to applications as needed, right?)
Used: A grand total of the above?
Free: free RAM

Then for each process, there's "Real Memory" used and "Virtual Memory." But if I total up all the "Real Memory", it doesn't add up to what's wired/active.

So.. how exactly does this work? For instance, my wired RAM is around 690MB, and active is around 373MB. But if I total up all the "real memory" for all the apps, it comes to 334MB. What gives?
 
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I remembered coming across this thread that explains it. Giulio's post includes a link to an Apple page that discusses it.

Edit: Sorry. There's nothing on the Apple page that explains why it doesn't add up.
 
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Yeah, that thread just states what's in the help file. Doesn't explain "real memory" vs "virtual memory" on the process list either.
 
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REal memory is physical RAM, Virtual is Hard Drive space that is used to act as extra RAM IIRC...
 
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Virtual RAM does not have any effect on the speed.
 
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Something still doesn't add up. Specifically, the "real memory" of each app does not add up to the wired/active.

Also, no way does "Virtual Memory" equal the HD based RAM an app is using, because nearly every app I'm running is eating up 300-400MB of RAM! Doesn't make any sense.
 
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Virtual RAM does not have any effect on the speed.
If you're saying the use of disk space as virtual memory has no affect on application speed, that is untrue when it is used. The read and write speeds to drives are many many times slower than accessing real memory directly.
 
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To answer the origial question simply start up Activity Monitor, select the Help menu item 'Activity Monitor Help' and enter the word 'wired' into the search box, hit the return key, then select the first reference that comes up. That was titled 'Checking system memory usage' for me in Tiger.
 
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I already read that help file. It doesn't explain my other questions/issues in this thread though.
 
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my processes -> all processes

It does work, you just have to click on the button that says "my processes" and select "all processes". Also, depending on what you're running using the purge command can help a lot (e.g., you're going through virtual memory because you've run out of RAM).
 

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