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There's a highly-rated app on the Mac App Store called FreeMemory. It claims to be able to "increase your free memory with a simple click." Although it's free right now, I believe it normally goes for 99 cents.

As a computer scientist, my intuition about the app is that it's almost certainly snake oil; in a modern operating system, anything the app could do would be unnecessary at best and actually harmful to performance at worst.

My best guess is that the app probably does something to cause the system to dump the "Inactive" memory, which probably has no effect whatsoever on performance. However, very little information is provided about the app, and I'm reluctant to install it on my machine. I'm also not as familiar with OS X as I am with Linux and Windows, so I could be mistaken about how OS X handles RAM.

My questions are:

  • What exactly does FreeMemory do, and how does it accomplish it? Is there some public API that can give user-space programs access to the operating system's memory management parameters?
  • Could using FreeMemory actually confer a performance boost, or is it snake oil as I suspect?
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3  
An excellent question! On of my biggest pet peeves is not only the dissemination of FUD but using it to swindle people out of their hard earned cash! –  cksum Oct 18 '11 at 8:28
    
Thanks for all the thoughtful answers. I actually installed "Free Memory" on my MBP as it seemed to really get bogged down switching between apps. With the FM app installed, it isn't really any better, and there is an additional irritation that as the app is "Freeing Memory", nothing else functions,.. at all,.. for 45 seconds or so. I don't think my MPB running OS X6.8 is really handling it's own memory well, but this app doesn't appear to be helping anything. –  user23051 May 21 '12 at 3:22

2 Answers 2

up vote 11 down vote accepted

Absolutely nothing other than swindle people out of their money. Don't ask me why Apple approved it. iOS and OS X manage memory as required. A lot of FUD out there claiming it's poor at it. No evidence to support those claims. No facts ever presented. No one with a modicum of experience or education in the field has ever come up (that I've seen) and accredited the claims. Snake oil.

You want to improve performance? Buy a better device. Only better hardware can equate to better performance. You can of course optimize a system, but this doesn't do that, it only shifts available memory.

Here's a breakdown of how to understand memory management in OS X (courtesy of Apple):

Free memory

This is RAM that's not being used.

Wired memory

Information in this memory can't be moved to the hard disk, so it must stay in RAM. The amount of Wired memory depends on the applications you are using.

Active memory

This information is currently in memory, and has been recently used.

Inactive memory

This information in memory is not actively being used, but was recently used.

For example, if you've been using Mail and then quit it, the RAM that Mail was using is marked as Inactive memory. This Inactive memory is available for use by another application, just like Free memory. However, if you open Mail before its Inactive memory is used by a different application, Mail will open quicker because its Inactive memory is converted to Active memory, instead of loading Mail from the slower hard disk.

Now even with rudimentary understanding of memory management in Apple's OS, tell me if you think "freeing up" Inactive memory is of any use? It is available to any application that requests it and if the same application wants to grab a hold of it again, it gets a speed boost. It's of course not this simple, but razing Inactive memory and moving it to Free memory results in no increase in performance. After all, how could it? A good system should hoard all your memory and allocate it to things that need it. Free memory is wasted memory as it's, by definition, not being used. If you have 8 GB of RAM and keep 4 GB free at all times, then you have a system running 4 GB.

Inactive memory in OS X is allocated intelligently. I'll change my tune when I see valid and reliable data that claims otherwise. And honestly, if nothing else, do you think some third party app has found the holy grail of memory management that has eluded Apple's world class engineers all this time (not to mention the thousands of contributing open-source UNIX programmers)? Like I said, snake oil.

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Note, the App is specifically OS X rather than iOS, but I like the answer. –  Nicholas Smith Oct 18 '11 at 9:43
    
@NicholasSmith iOS manages memory in very much the same way as OS X. It's file structure is also identical and so is very much of kernel architecture. For such low level functions, you can speak about iOS and OS X interchangeable (obviously iOS is tweaked to run on the ARM7 arch, but for our intents and purposes, we needn't worry about that), but that is off topic and I edited my answer to better focus on the OP's question. Thanks. Don't know why I wove iOS in there... gotta learn how to read better. –  cksum Oct 18 '11 at 9:57
    
the similarities are why I liked it, you get to see how OS X handles under limited memory circumstances more readily via iOS. –  Nicholas Smith Oct 18 '11 at 10:08
    
@NicholasSmith that's a good point, and should add further support that all those memory management apps (iOS and OS X) do absolutely nothing (a shame Apple approves them; at the very least, they seem "dishonest"). –  cksum Oct 18 '11 at 10:14
    
Why is it that my mac would rather start swapping like mad even though there is over 40% of my memory as "inactive" –  XAleXOwnZX May 21 '12 at 4:12

Installed and tested, they're running the purge command and freeing up inactive memory. It's not 100% snake oil, there can be situations where OS X doesn't properly release the inactive and starts hitting the disk based swap file (incurring an I/O performance hit), but it's fairly useless for the majority of users.

Although if they're making $0.99 for wrapping a command in a menu bar I really need to get my Mac Developer license.

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