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I remember the times when I got my macbook pro with 4GB of RAM: I could launch Firefox, VirtualBox and Firefox inside a VirtualBox and it worked reasonably well.

Two years later, when I start the system and have no programs launched, 3.99 out of 4GB of RAM is used; and launching any tiny program, making ⌘ Cmd+Tab or a new tab in a browser is a huge pain for Mac OS X: I have to wait for dozens of seconds for any little action to complete.

However, if I sum up the "Memory" column in Activity Monitor, it would barely come up to 700 MB; Swap is low, File Cache does not exceed 300 MB.

Memory usage

So I don't really understand what could have happened with my Mac and what can I do to take it back to the times when I could use Firefox and Skype together without any slowing down.

Screenshot with all processes as suggessted in comments:enter image description here

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Can you add the process list (from the Memory tab) out of Activity Monitor to your question as well? –  patrix Dec 9 '13 at 8:11
    
Two years ago, what was you Mac OS X Version ? –  Larme Dec 9 '13 at 14:28
    
Two years ago I had 10.6, the lags started on 10.6 as well. I switched to 10.9 a few weeks ago in hope to have some speedup, but no results. –  Ixanezis Dec 10 '13 at 6:50
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1 Answer

The "Memory Used" number doesn't mean what most people think it does. Modern operating systems pre-fetch a lot of things from the disk to make things seem faster when you actually request them. For example, in your screenshot, 1.47 GB of the 4 GB "used" is the file cache, which OS X will delete if an app needs more memory. A better metric to look at is App Memory (1.57 GB) compared to your total memory (4 GB).

In the screenshots, it should not be slow because you have barely used any swap. Once the OS starts using swap (more rare with Mavericks), it will start feeling slow. Some people think there are bugs introduced in Lion in OS X's dynamic pager (manages the swapfiles) that cause the system to thrash before it needs to. (I assume) Apple engineers use fast computers with SSDs, which hides this problem.

The solution is to buy a crapton of RAM so the OS doesn't have to hit the swap or downgrade to the earliest OS supported by your computer.

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All right, I see the "Memory used" is probably not the reason of slow behaviour. My complaint is "Why do I have to experience heavy lags or extend RAM if my apps only use 1.5 out of 4GB?". Moreover, it was all fine earlier and started being slow also on 10.6. BTW, there's another Windows 8 PC with 4GB RAM, running a lot more heavy programs like MS Office, Photoshop and VMWare simultaneously without any problem. A bit disappointing. –  Ixanezis Dec 10 '13 at 7:07
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To see if it's a problem with some software you installed, you could try making another partition and doing a clean install of OS X on that partition. I haven't really looked into the issue. I will say that I used to use a Mavericks Mid-2010 MBP with 4 GB of RAM and a spinning hard drive, and when everything is backed by RAM, it was pretty fast. –  Kevin Chen Dec 11 '13 at 7:10
    
Thanks, I'll try it out. –  Ixanezis Dec 11 '13 at 8:56
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