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I am looking for clarification since I am seeing large allocations of RAM on my Mac. I have 16 GB of RAM and recently installed Windows 7 on Parallels. When the machine runs, I see 3.55 GB Free memory and 8.39 GB Inactive memory. I do not want my RAM to be hogged by Windows if I only need it for a small task and am concerned about a slowly running Mac in this case.

Might the huge amount of inactive memory be due to Parallels being run recently? I am not sure if Parallels is the culprit. Moreover, Wired and Active memories show 2 and 2.13 GB, respectively. The total Used memory is 12.54 GB which means the majority (12.54 GB of 16 GB) of RAM is committed now.

This seems too much. How can I diagnose what is exactly eating up my RAM? I have a retina MacBook Pro and the 10.8 release of Mountain Lion. When I launch Parallels, the increase in memory is allocated to "Wired" yet Inactive memory is still 8GB.

Is what I am seeing explainable?

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2 Answers 2

up vote 9 down vote accepted

Free memory has nothing in it. Inactive memory caches recently used information just in case the system might use it again. This is especially beneficial for file storage.

The system only needs a tiny amount of free memory so the program asks for memory to be allocated it doesn't have to page some other active memory out to disk and cause that program to stall momentarily while the virtual memory system is doing housekeeping. The overhead for the system to release inactive memory is almost immeasurably short so worrying about a large amount of that memory is generally not worth your brainpower to even think about it.

In summary:

  • Inactive memory: this is always good, it makes the system fast.
  • Free memory: any more than 200 MB is a waste, so the system will keep adding files and/or code to inactive memory until free memory hits a low-water benchmark based on a few factors.

What you describe seems perfectly normal for a system that has been recently booted and doesn't seem to me to be anything of concern. VMware fusion or Parallels clearly has need to access a lot of files when running Windows 7 and they are likely to be the reason for your large amount of inactive memory.

If, however, you wish to diagnose what is using memory, the sysdiagnose program will run several memory allocation utilities and saves the results to a directory.

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Haha do all members like editing each other's posts that much ? :P –  Render Aug 14 '12 at 19:12
2  
Yes - this site is quite collaborative and we err on letting people make edits. When someone feels it's not perfect they of course get to roll back changes and optionally explain why, but this site is fairly hands on in terms of editing. –  bmike Aug 14 '12 at 19:16

I'm a designer and what's happening to me is barely the same. I'm using Snow Leopard and have a MacBook Pro 15" (i7) with 8GB Ram, 500GB (180GB free) (2010 model).

I usually use Chrome (4/5 tabs), Firefox (1/2 tabs), Skype, VM Ware Fusion (with Win XP, using only 512MB), Photoshop CS5, Adium, iTunes, maybe Filezilla.

Photoshop is the main Ram user. It can eat up to 3GB or more as time rolls by, and I'm not working with very big files, 50mb max, and only 2 or 3 open.

When you start opening programs everything works fine. It's later on that you see that you have very (and I mean veryy) little Free Ram left. Between 8MB and 15MB. At the same time I have 2.21 GB of Inactive Memory.

The machine gets much slower once you get below 150MB of Free Memory, and it's a total lie that Inactive Memory gets released onto other programs to overcome this slowness. It never gets released until you close the program.

I wanted to post a screenshot of my Activity Monitor but your site doesn't allow it if I'm a new user.

Once your Free memory gets to these levels (15MB), the Page Outs start increasing and the Inactive Memory never gets released. It gets laggy.

Please don't tell me that a 2010 Macbook Pro with 8GB is not enough to work with Photoshop on small to medium sized files. Normal users (internet, skype, movie watching, etc.) won't have this problem, but if you use it for design or more heavy tasks, it doesn't work properly.

I think this is a very important issue that has never been addressed. I don't know if Mountain Lion has solved this, but I've been searching around and haven't read good commentaries (they even say Mountain Lion eats up more Ram).

Do you know if a MacBook Air i5/i7 8GB 256GB SSD will improve on this matter? Do SSD's improve Ram usage? I'm planning on changing the MacBook Pro (not because of this, because of it's size).

Thanks, Jimmy

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