Found in the Utilities folder with the Applications, chances are you have probably opened it up once or twice for something. Its main function is to display all the current running processes, along with their memory and processor usage. What it also shows you is the drive space, RAM space, network activity, CPU activity, and disk activity to name a few things.

CPU – This panel will display all the information pertaining to the usage of the processor. The first thing you will notice when viewing the process list is that 100% isn’t the maximum. The way the computer calculates percents for processes is based on every core operating at 0 to 100%, meaning if you have two cores, you’ll have a total of 100% processing power, 4 cores 400%, etc. Contrast this with the summary (lower panel) which runs from a strict 0-100% scale, meant as an overview to the system, rather then a detailed look as is the process view. The “% User” which is green by default, indicates the percent of the processor that tasks that belong to you are using. These tasks include pretty much anything that opens when you log in, as well as anything you manually open or run. “System” includes things that load up when the system is started as well as processes that cannot be terminated and that are necessary to the operation of the computer. “Nice” is a bit more complicated. The Nice processes are those which are running under a scheduled order – that is processes that are given a priority, to either be executed ahead or behind others. You will usually see the Nice increase along with heavy multitasking actions, such as some Photoshop plugins. Read more