virtual memory - does it slow my system down?

Do you know what "virtual memory" is? Virtual memory - Wikipedia, the free encyclopedia. Do you know what you are looking at in Activity Monitor? That information is strictly for developers. It means nothing to you or what your computer is doing.

That didn't "fix" anything. There has to be something wrong for something to get "fixed." Wait a few more hours and you'll likely see the same thing. That's because you really don't understand what those numbers mean - nothing to the user. There is nothing to fix. Memory usage of all kinds will drop after you reboot any computer.

200 to 400 GB of Virtual memory is just promises. Only a problem if it all comes due at once.

Use this Activity Monitor setup to look around.

Using Activity Monitor to read System Memory and determine how much RAM is being used

If you have less than 1/6 pie of green, you may be getting into trouble. If you have a non-trivial amount of PageOuts, you are in trouble.

It might be normal if you haven't rebooted for a long long time. Reboot ahd it will shrink again.

Look at Avtivity Monitor System Memory and read this to determine if you need more ram to boot your performance.

Using Activity Monitor to read System Memory and determine how much RAM is being used

Virtual in that scenerio is not real page out VM, it is "address space" and 140GB is very normal. When you boot using 64-bit kernel mode, guess what? those figures are higher.

Go To Folder /Var and take a look in VM and count how much actual page files there are.

If it was "real" your drive would crash but OS X would warn your first.

Disk drive space: boot drives: keep 35% or more free. That means yes it is good to not have anything but the OS and apps and mini home library.

For a 900GB drive that does mean 300GB free - you don't want slow long disk I/O seeks to find and write files and cause the disk to "thrash" about. And why SSD which have gotten cheaper can be ideal boot drive - $120 / 120GB or 240GB / $200. Along with 1TB / $120 to hold data files.

12GB should be fine for even medium work load with graphics. For what you were doing you might want to try with a guest or trial user (standard user) account.

Heck.... now we won't know just how many files, and total of all those files (64 - 128 - 512MB etc)

The basic operations of the OS require a certain amount of swap space of their own. If you look in /private/var/vm (you may have to use the finder Go menu to look), and I say look, never touch, you will see the swap files created for the VM. Initially after reboot there will be only one file. With time the number of these swap files tends to increase. Depending on your total ram and how many new apps you start running over time having a larger number of these swap files will affect performance. That's one of the reasons your performance improved after rebooting.

What's a large number of swap files? Like I said that depends on your particular usage and ram. I only point this out to give you some way to try to correlate some of your performance slowdown with the number of swap files in see in /private/var/vm. Over time you should get a feel for your machine and when the number of swapfiles you see is "too much" and you should reboot.

Keep probing and watching.

How large a disk drive is the system on?

What else is running?

Maybe use Top command and some numbers to show real and virtual sorted output.

PageOuts is a "water meter" type counter.

A high number after a few days is nothing to worry about.

A high number after a few minutes could be a problem.

With respect to watching youtube videos, a lot of them are "choppy", i.e., rebuffering "pinwheel", particularly since google took it over. I see it too, and I have 24GB 6-core 3.33GHz mac pro with a 12 Mbps internet connection. I suggest you try lowing the resolution of the video (click the little gear in the bottom right of the video screen).