iStat Pro Memory Question

[slackersonly]

20" iMac Core Duo with 1.5GB RAM

I have been studying the memory section of iStat Pro as I have had increasing delays in Safari lately (ie. beachballs of frustration). What, in basic terms, do the 4 categories of memory used mean?

Wired
Active
Inactive
Free

After using the computer, I seem to run very low on free memory. Closing programs does nothting to change this. Rebooting does but that it not a good workaround.

Am I really running low on RAM?

 

[WildCowboy]

Free memory is not important. What is important is free + inactive memory. Inactive memory was used by an application at one time, but has been released to be reallocated if needed. It retains the old data in case you happen to reopen the previous application.

Wired memory is what contains core kernel processes and can't be paged out to disk if you run low on memory.