System Monitor can be started by double-clicking its icon in the Finder or Dock. When using Mac OS X Lion or later, Launchpad can also be used, of course. After launch, the following window will appear which allows you to manage all features of the app as desired:
The highlighted left side of the window shows different areas that you can control. We refer to it as sidebar. The individual items within the sidebar are thematically arranged sections that you can select by clicking. After you have selected an item, its settings will appear at the right side of the window.
The window can be resized as usual, by dragging its lower right corner. If the window is wide enough, you can additionally resize the sidebar, determining the portions which are used for sidebar and preferences. You can do so by using the small handle in the lower right corner of the sidebar.
In addition to the control window, the actual display area of the app will be shown simultaneously at the right side of the menu bar of Mac OS X. The display of System Monitor is always added left to other icons which you might already have in the bar. So the display is placed on the right side, adding items from right to left. The menu of the currently active application remains always on the left side of the screen.
If your screen should not be wide enough to display the menu of the currently running application (left) and the added symbols (right) at the same time, the menu of the application will always have higher priority. Menu bar icons will disappear automatically from left to right until enough space is available. When more space will become available later, the icons will automatically reappear.
In case you mistakenly remove all monitoring items of System Monitor, the menu bar won't become empty. In this particular situation, a crossed rectangle (⌧) will appear as a placeholder to indicate that System Monitor is still running.
In normal operation mode, System Monitor will show a summarized overview of the data directly in the menu bar. More details can be unveiled for each monitored item by opening the respective menu of the individual icon. You only need to click on the respective symbol with the left or right mouse button. Which details are available to be retrieved can be customized individually in most cases. Another click on that area in the menu bar will close the menu again.
At the bottom of each menu, you will always find the item Preferences…. After selecting such an item, the control window will be shown and the matching section with the associated preference settings will be opened.
You only need the control window when you like to make changes to the configuration of System Monitor. After all settings have been made as desired, you can close the control window which also makes it possible to remove the icon of the app in the Dock. The display in the menu bar should usually be shown all the time, however. For this reason, these two parts of the app are independent of each other. A setting in the program defines how the display in the menu bar should behave when you quit the System Monitor app, or close its control window, respectively.
Perform the following steps if you like the menu bar display to appear only while the control window is running. The steps can also be used to permanently remove the display from the menu bar:
The next time you close the application or control window, the icons in the menu bar will be switched off.
Reverting the setting causes the display in the menu bar to be displayed each time you log into Mac OS X:
You can skip this section during first reading. It describes particular rules defined by Mac OS X for the display of menu bar items.
There is a special order of rank for icons appearing at the right side of the menu bar:
At the rightmost position, you'll find the icons provided by Apple which are part of Mac OS X. These icons are called Menu Extras. They can be moved, bringing them into any order. To relocate these icons, perform the following steps:
Similarly, Menu Extras can be removed from the menu bar:
Left to the Menu Extras, you'll find the displays of applications which are not part of the Mac OS X package. They are called Status Items. Although there are no visual differences, Status Items are following other rules: They cannot be relocated, they cannot be removed by pulling them down, and they can be added from right to left only, keeping them always left to the Menu Extras.
Apple strictly monitors compliance with these rules. Menu Extras and Status Items must not mix. Because System Monitor is not part of the Mac OS X package, it constitutes a Status Item. For this reason, the app's individual icons in the menu bar cannot be moved by the mouse.
If you switch certain icons of System Monitor off and then reenable them, those icons will be considered to have been “recently added”, so they can be lined up to the left of the remaining icons only. This can cause their normal sort order to be lost temporarily. You can manually readjust the order of items back to their default order or to your personal preferred order easily, however. Further information can be found in the section Customizing Layout of the Menu Bar Display.