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.

System Memory – There are more ways of looking at memory usage then you can shake a stick at. The two basic ones, and most important, are the Real Memory and Virtual Memory. Real memory is the amount of actual RAM being used, while the Virtual memory is the page size – the amount of space a program takes up on a disk, incase it runs out of room in RAM. You’ll notice the Virtual memory is usually quite high, sometimes in the order of 10+GB; the process isn’t usually actively taking up this much space, but rather is allocated this amount in the event should it need it. On the “System Memory” panel, “Free” is as the name implies, the amount of free RAM. “Wired” is RAM that is currently being used by a process that cannot be terminated (such as a System process). “Active” is RAM that is currently being read or written to, while “Inactive” can be either a program that was previously closed and kept in RAM incase you reponed it (to decrease launch time), or an open program that hasn’t been used in some time. Processes in the Inactive category are the first to be moved into a page file should it become necessary. “VM Size” indicates the total maximum size of the virtual memory, should the computer need to utilize that amount. “Page ins” and “Page outs” are the amounts of data actually written to and read from the virtal memory, while the “Swap used” is the total virtal memory being used.

Disk Activity – Ever look at an older PC and notice the flashing green light in front indicating drive activity? This is your flashing light. This panel displays the amount and speed of access to the drive. A “Read in” and “Write out” is defined as an access. Access is any time the computer needs to either write something to or read something from the drive – basically any time the needle has to move. The numbers you see reported aren’t in singular, but usually reported in thousands or millions. “Data read” and “Data written” as you might imagine is the total amount of data moved on and off the drive. Expect this to easily ready the order of 1+GB even without opening any programs. Bellow the graph, you’ll notice two options – “IO” and “Data”. IO is a rather obscure measurement, while “Data” is the more relevant one, displaying speed in amount per time (usually either KB or MB/sec). The “Peak” displayed above the graph is a peak for the time period of which the graph covers, not a value of the peak of all time.

Disk Usage - The “Disk Usage’ panel is rather straight forward in comparison to the others. It displas a dropdown menu of all currently mounted drives, along with their free and used space amounts. Although a GB (Gigabyte) is suppose to represent 1,000,000,000 bytes, practically speaking in todays IT world, it represents 1,073,741,824 bytes, accounting for the discrepency between the two amounts listed next to eachother.

Network – If you understand the earlier “CPU” panel then you’ll understand this “Network” panel largly the same. “Packets in” and “Packets out” are the amout of packets transfered by the computer. A packet is a small chunk of information, the size of which is usually very small and determined by the network settings. “Data recieved” and “Data sent” is as the name implies, the amount of data moved through the network. This is not the amount of data you have transfered over your intnernet connection, which is usually significantly less, due to a lot of the transfer protocols which take up some bandwith on yoru internatl network. Likewise with the Peak from the “Disk Activity” the peak here is limited to the coverage of the graph, not of all time.

Inspect – The insepct button allows you to basically see all of the data from the panels on the bottom for one specific process. This is useful for checking to see how many recorces a particular program, or part of a program, is using. Some of the information provided there is a bit advanced, while some is identical to the summary display.