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I am using OS X 10.5.8 and in spite of having 5GB of RAM memory, I face a lot of inactive RAM, and go to the terminal and purge it via the "purge" command (of course without quotes).

I do this almost every two days, some application(s) is(are) probably not freeing up memory.

I would like to know if this command is harmfull/if it can "damage" anything in the system/in open applications?

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In general, it should be unnecessary to use purge unless you're trying to do performance testing by flushing the disk cache, which causes page hits to take longer, because it has to read them back into memory. What are you trying to accomplish? Memory marked "inactive" (displayed in blue by Activity Monitor) is memory that hasn't been touched recently, so the OS will page it out before "active" memory, but inactive memory still contains data that may not be on disk, so it will take time to write. And, purge can also purge active memory and usually causes severe computer slowdowns. –  Chris Page Jun 29 '12 at 13:13
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up vote 3 down vote accepted

No harm will come to your system through using the purge command. The purge command clears out pages which have been written to memory which the system thinks it may need again. Usage of purge can cause some applications to temporarily run slowly if resources need to be reloaded.

From the purge man page for Xcode 3.2.5:

DESCRIPTION

Purge can be used to approximate initial boot conditions with a cold disk buffer cache for performance analysis. It does not affect anonymous memory that has been allocated through malloc, vm_allocate, etc.

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I was waiting for more answers, but yours seems to answer it, I'll accept it. –  jackJoe Jun 29 '12 at 12:03
    
"Clears out pages which have been written to memory" is probably not a good description (and "memory" is likely a typo for "disk"). It writes any unsaved data to disk, then marks the memory as unused, so the data has to be re-read from disk the next time it is needed. –  Chris Page Jun 29 '12 at 13:10
    
The usage of the word "memory" versus "disk" is not a typo. Additional info on memory states can be found in KB Article 1342. –  DMan Jun 29 '12 at 15:59
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