Limited Available Memory, is web browsing effecting logic? Options

[miaba]

Hi, I'm wondering if anyone can briefly explain the pie chart in the "system memory" section of the utlity monitor. I'm noticing that as i surf the web there is a decrease in availability within memory. This is a concern because i need everything i've got to get the best performance out of logic. Any advice, tips, or ideas are welcome. I'm considering a re-instal if necessary.