Why is 70MB of my RAM 'inactive'?

[joefinan]

In the activity monitor I have 540MB active and 2.97GB free (which all makes sense) but what is 443MB of 'wired' and 68.99MB of 'inactive' memory?

 

[xUKHCx]

I suggest you read Mac OS X: Reading system memory usage in Activity Monitor for a full picture but the specific parts are.

Wired memory
This information can't be cached to disk, so it must stay in RAM. The amount depends on what applications you are using.

Inactive memory
This information is no longer being used and has been cached to disk, but it will remain in RAM until another application needs the space. Leaving this information in RAM is to your advantage if you (or a client of your computer) come back to it later.

It is perfectly normal to have these numbers