Um, no. Read the developer docs, or just look at your inactive memory use over time and you'll see this person is utterly misinformed...

Um, yes. It doesn't do what the developer docs says it does, just as described in link. I've observed it myself. Yes, inactive decreases as well as increases over time, but immaterial to the fact that inactive still gets paged to disk — doesn't matter whether it's "only" modified inactive; *no* inactive should (defeats the purpose!). Watch the swap files pile up!... If it's a scam, then why does my excruciating sluggishness go away when running FreeMemory-type utilities (or purge in Terminal)? Without them, I'd have to go back to rebooting every time this happens.

If inactive is dirty, it will get paged to disk, that is exactly as it is supposed to do. I've never seen excessive Page outs unless they were genuinely needed (I'm at the limit of my physical memory use). Swap is allocated in larger chunks than the data that is written, do not look at the Swap used as an accurate indicator of what really is in the backing store.

Are you sure. I manage about 8 Mac Pros and several laptops in our lab, we run computational models of neural circuits, extensive data analysis in Matlab, generate scientific graphs in CS5, and run Parallels for some legacy software and have never seen lots of free/inactive memory yet lots of paging out. I see exaclty what I'd expect, and given the long history of hoax memory optimisers, FreeMemory is certainly no different in conception.

Yes, I'm sure. I've personally observed the undesirable behavior at least as far back as 10.4 Tiger.... Inactive should *never* be paged to disk, no matter what TheWormyFruit™'s docs say; to repeat, it defeats the purpose and the thrashing unnecessarily slows down the Mac.... Linux & other Unix-type OS apparently don't do this for the most part, it's all Apple arrogance... Some of the heavy-lifting things you described you do themselves may be purging inactive as you use them, similar to what FreeMemory-type utilities or repairing permissions do.... Nevertheless, it's not consistent & many Macs don't overtly experience it — sometimes there seems no rhyme or reason to it.... In any event, the acid test is that when one *does* chronically experience it, and purging inactive by any means (or rebooting to do so) restores robustness, I'm going to keep doing it, so I can get some work done instead of fighting the goddamned computer.

You are incorrect. Here is what happens in the Linux kernel:

"Pages of memory are either Free (available to allocate), Active (in use), or Inactive. Inactive pages of memory are either dirty or clean, depending on if it has been selected for removal yet or not. An inactive, dirty page is no longer in use, but is not yet available for re-use. The operating system must scan for dirty pages, and decide to deallocate them. After they have been guaranteed sync'd to disk, an inactive page my be “clean,” or ready for re-use."
http://www.linuxplanet.com/linuxplanet/print/6593

IF the inactive page is dirty, sync it to disk. Then free it.

And OS X:

"In Mac OS X, if an inactive page contains data that has not been written to the backing store recently, its contents must be paged out to disk before it can be placed on the free list. "
https://developer.apple.com/library/mac/#documentation/Performance/Conceptual/ManagingMemory/Articles/AboutMemory.html#//apple_ref/doc/uid/20001880-99406-TPXREF103

IF the inactive page is dirty, page it to disk. Then free it.

Countless highly trained computer science engineers have built the virtual memory system across multiple OSes in this way. Do you really think a single line command or some two-bit app developer[1] somehow can do something the most highly skilled (and in Apples case probably richly paid) CS engineers have failed to understand for years? Again, read The Memory Optimization Hoax by sysinternal engineer Mark Russinovitch (Windows VM is largely similar).

You probably have something seriously wrong with your software somewhere, it certainly isn't OS X / Linux VM memory subsystem, and I still doubt placebo purging is really helping.

----
[1] I contacted Rocky Sand some time ago and they told me they would put some reference to the criticisms of their software and a discussion of both sides of the memory optimisation debate on their page. They never did, their vaguely worded FAQ is useless. That smacks of hoax two bit software to me.

I find it interesting that no one has questioned why Apple would make this available in the App Store. If it is as totally useless as most seem to believe, that leads me to wonder why Apple continues to allow it to be sold. Could they need the .99¢ that badly? Or do they really not care?

Not only are they useless, they actually SLOW your Mac by flushing caches that were put there in the first place to speed it up! Any developer who tries to convince you that such apps are beneficial is either lying or stupid.

Sorry. The UI here ate some of the characters in my instructions. Let me try again using [R]:

1) Open a Terminal window.
2) Type on the command line:
purge [R]
... where [R] means hit the Return key.
3) When the purge process is finished, close the Terminal app.

You're done.

$ sw_vers
ProductName: Mac OS X
ProductVersion: 10.6.8
BuildVersion: 10K549
$ man purge
No manual entry for purge
$ type -a purge
-bash: type: purge: not found

@ Hal Itosis - hi, I may be mistaken but I believe the purge command comes as a part of the Xcode Apple Developer Tools install package; it's not included on a standard OS X install. =)

@Tommy_b: i have no idea if you're mistaken or not. But either way, such info was lacking in the OP.

There's a reason it's only included with the Developer Tools - it's for developers to dick around with memory while developing their software:

"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."

End users do not need (and should not screw around with) "purge", not even the ones who think they're "advanced" users, and _nobody_ needs FreeMemory. Apple and Mac OS X handle the complexities of memory management (such as ASLR) far more effectively than some random amateur developer who is still thinking in Mac OS 9 terms.