It's faster than swapped memory since it's already loaded in RAM and accelerates things when the virtual memory system makes good guesses. It serves as free at a moment's notice, but also makes repeated tasks much, much faster if the system guessed correctly and kept something in RAM that you will do again. Inactive memory is bonus speed / double duty RAM.

The problem arises when Free+Inactive is less than roughly 1/3 of the total and then things can really get slow. For largest allocations, it simply uses some of the Inactive RAM by allocating it to active/wired and removing the information on what it used to hold.

Free: Totally Wasted RAM - the system only needs one or two MB free to cover short term allocation requests.

The same things happen again and again on computers. Engineers know better, you will go back to Facebook in a few minutes or re-launch Word after quitting it.

Inactive: Things that programs have read from the slow disk or elsewhere and said they never need again.

Active: Programs are really using this memory now or in the last few seconds.

Wired: The system cannot run without this amount of RAM (never swapped).

Here's how I explained things to someone new to the concept of virtual memory on OS X: It should have been called something like 'make your Mac really fast the second, third, and fourth time it does the same task' memory except that's an awful name, too.Īpple re-wrote the activity monitor when it introduced several new features and added compressed memory, so some of this no longer applies to macOS that don’t show “Inactive Memory” but this still applies to Mac OS X memory management as documented against this version of Activity Monitor: Inactive memory got a horrible rap due to a crappy name.

How to clear memory on mac