[nemanirc]

In the activity monitor, what is "wired" RAM? Why is some RAM "inactive"? I just opened iPhoto with a large library (1086 photos) and it soaked up 232 MB of my 896 MB, but most of it seemed to be in inactive RAM. Why is this?

[eevyl]

I will paste a email I sent as a answer to a very similar question on a mailing list.

87.0M wired means you have ........ ?

It means you have 87 MB of memory that needs to be in physical RAM all the time, no matter what. This is usually the case of the OS kernel, drivers and similar hardware things.

616M active means there is .......... ?

It means there is several applications actively using 616 MB of physical RAM, usually from applications running (from the OS itself or the ones you launch).

308M inactive .........

This one means there are 308 MB of RAM not being used by any application at that time, and it may be swapped to disk if there is need of active RAM for other applications. It also can be memory left by an application quitted, OS X memory management keeps some chunks in physical RAM if there is space just in case you relaunch it later (this is why applications usually launch faster after the first launch, on the same restart of course).

1011M used ........

The sum of wired, active and inactive.

13.2M free ...........

Free memory for OS X is wasted memory, this is memory no one is using at the moment.

So if you look for "available" memory, you should look at the sum of inactive and free memory.