Why am I having less free memory? What is active and inactive memory?

Question

Hi, I own a MBP penryn model. Right now, when I look in the activity monitor (or istat pro), it tells me that my free ram is 302mb, 56mb inactive, 816mb active, and 166mb wired. Why am I only having 300mb free if Im only using safari at the moment and not running anything else? Everytime I start up my notebook, the free space is around 1.70gb free at least. But why do I have that little bit of free space after a long time use?
Sorry if this is a newbie question, im really new to this.
Message was edited by: djvic87

Answer 1

About OS X Memory Management and Usage
Reading system memory usage in Activity Monitor
Memory Management in Mac OS X
Performance Guidelines- Memory Management in Mac OS X
A detailed look at memory usage in OS X
Understanding top output in the Terminal
The amount of available RAM for applications is the sum of Free RAM and Inactive RAM. This will change as applications are opened and closed or change from active to inactive status. The Swap figure represents an estimate of the total amount of swap space required for VM if used, but does not necessarily indicate the actual size of the existing swap file. If you are really in need of more RAM that would be indicated by how frequently the system uses VM. If you open the Terminal and run the top command at the prompt you will find information reported on Pageins () and Pageouts (). Pageouts () is the important figure. If the value in the parentheses is 0 (zero) then OS X is not making instantaneous use of VM which means you have adequate physical RAM for the system with the applications you have loaded. If the figure in parentheses is running positive and your hard drive is constantly being used (thrashing) then you need more physical RAM.