System Monitor can monitor the current load running programs put on the central processing units, the processors of your computer. If the load per processor is at 100%, this processor will be fully utilized, so it will be running all the time, without any interruptions. If the load is at 50%, this will mean there was not enough to do for this processor: After half the time available, it was “finished”, having completed all tasks, or it had to wait for data from other, slower devices, e.g. the hard drive, so it was idle for the remaining 50% of the time interval measured. Modern processors are actually shut down during these idle times which saves energy and significantly reduces operating temperature.
If you like to monitor the load of the system, perform the following steps:
When this option is enabled, the total load of the system will be shown in the menu bar. This is equivalent to the average value of the load of all available processors. In case all available processors are fully utilized, the total load will be 100%. If you had 4 processors, for example, one is fully utilitized, and the other three are idle, total load would be 25%. Alternatively, you can configure the display to show the individual loads for each single processor (see below).
The data shown is calculated live and updated about once per second.
The box Menu Bar controls in which form total load should be displayed. System Monitor offers a variety of icons and functions that you can combine in any order. The following elements can be used:
Within the box, the upper bar simulates as a sample how this monitor section should be presented in the menu bar. You can grab the individual items by mouse and move them into a different order. You can remove an element by pulling it out of the bar. The lower bar contains the stock of items available. If you like to add a certain item to the menu bar, use the mouse to drag it from the lower to the upper bar. Pressing the button Default causes your current settings to be deleted, replacing it by a default suggestion for the menu bar.
Spacers are shown with dotted rectangles to make it easier for you to recognize and to move them. In the actual display, the rectangle will become invisible, so the spacer does its job providing a blank area within the menu bar.
If you mistakenly have removed all items of this monitoring section from the menu bar, a three-star-icon (⁂, asterism) will appear as a placeholder. This ensures that you still can open the associated menu.
You cannot drag items directly into the real menu bar.
In standard configuration, the menu bar shows the total load for all processors of the computer. You can replace this display by individual displays for each processing unit if you like. All display elements will be reduplicated for each processor in this mode which can consume much more space in the menu bar. The text CPU is hereby replaced by Pxx where xx is the number of the respective processing unit. To enable this feature, switch the pop-up menu below the box Menu Bar to the item Display loads for each single processing unit.
At least the following items will be shown as part of the menu associated with this monitor section:
The reading Reduced is also known by the term nice in computer jargon. A process that runs with reduced priority behaves “nicely” and modest in respect to the remainder of the system. It will only occupy the processors when nothing else has to be done.
You can also include the following items in addition:
Show top 5 processor consuming processes: When setting a check mark here, System Monitor additionally collects information which currently running processes are responsible for the major part of the load. The process names will be listed in one section of the menu, sorted by their contributions to the total load. The corresponding percentages will be listed as well.
Retrieving the process list is a costly operation for technical reasons. The load caused by System Monitor itself will slightly increase when you enable this feature.
To show the full list of processes, you can quickly open Apple’s Activity Monitor application. Select the item Launch Activity Monitor in the menu.
Additional load graphs: In addition to the total load value in the menu bar, you can also insert further history graphs into the menu, showing the detail load on each processor for the last 30 seconds graphically. You only need to check the respective processors in the table. By pressing the buttons All or None, you can automatically add all processors, or remove them, respectively.
System Monitor sees the processors from the same standpoint as the operating system; it does not use the point of view of the hardware. A processor is a processing unit administered by macOS, no matter if it is located on an individual chip, or only as a processor core within a chip. Some processors use special technology to emulate more processing units than actually available.