It's because your application is reserving memory but not looking at
most of it. What happens is that OS X swaps things in RAM out to
disk when they are not recently used. Do a google on "how virtual
memory works" to understand more.
On Nov 30, 2007, at 9:59 AM, Kenneth Prager wrote:
I have a question regarding an application's real memory footprint
versus its virtual memory footprint. I am asking this question
here because (a) I know that there are many knowledgeable people
here and (b) I honestly don't know which other of the Apple lists
is more appropriate (is this a Darwin question, a Cocoa question,
etc.). Also, I am asking this question only because I am curious,
not because I expect to do anything with the information.
Here is my question: when I reboot my Mac, it starts out with one
swap file (BTW, I have 2 GB of RAM). If I look at memory usage in
the Activity Monitor, real and virtual memory footprints are the
same. After about a week I am typically up to 5 or 6 swap files
and for most applications, the virtual memory footprint is 10-15
times as large as the real memory footprint (for example, PCalc's
real footprint is 6.7 MB and virtual footprint is 364.5 MB).
Why is this? Is it because of a lack of garbage collection in
Objective C? If so, will the addition of garbage collection in
Leopard automatically solve this problem?
Thanks in advance,
Ken Prager
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