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Working with the application

Usage Information

Basic operation

To use the tool, double-click its icon, enter the number of processors you want to control into the field Numbers of processors to load, and select the desired load with the slider.

Control window of SystemLoad
Control window of SystemLoad

How can I verify if SystemLoad is working?

Launch the application Activity Monitor which is part of every macOS system. You can select any of the possible monitoring displays, e.g. Window > CPU History. It will display the load on each processor over time. On the command-line, you can use other tools like top or ps to monitor CPU activity.

Why can the actual CPU load be higher than the one set with SystemLoad?

The application can only control the load it generates itself. If you have other applications running, these applications might also put load on the processors. Because the design of macOS guarantees that no application (except the operating system core itself) can “steal” processing power from other applications, you cannot make SystemLoad generate a load which is lower than the current load on your computer. The load set with the slider is the additional load on the processors.

Why is the load displayed by a monitoring program not always exactly the same load as set in SystemLoad?

A variety of factors has influence on the actual load display: CPU Monitoring applications have to measure the processor load during a certain time interval. Because macOS continuously reschedules processor time depending on the current total load, the SystemLoad application may have received varying parts of the totally available processor power during the measurement interval. While SystemLoad tries to generate an exact load in the system, other events could cause the measurement to become inaccurate. In particular, this is the case for systems with multiple CPUs because macOS might decide to place the application onto different CPUs during the interval. So a 50 percent load defined for one processor may for example appear as 60 percent load on CPU A and 40 percent load on CPU B on a dual CPU system.

To generate a load as accurately as possible, you should quit other running applications.

Can SystemLoad cause any damage?

No, SystemLoad is a standard application which lets your computer compute. This is what your Macintosh has been designed for. The only special thing about SystemLoad is that can control exactly how much computations are done and when they take place. This cannot harm a functioning system.

Of course SystemLoad has been developed to detect hardware problems. This means if your hardware is already defective, SystemLoad will most likely expose this defect. For example if the cooling system is not working correctly and you put maximum load onto the system, your Mac might shut down because it is exceeding its temperature limit.

What will happen when I switch the mode at the bottom of the window?

When you select the button Try to play a scale on voltage supply circuits, the application tries to variate the load put on the processors in a certain pattern. This pattern is equivalent to the frequencies of a C-major scale between the notes C6 and C7. For processors consuming much power this causes the current (amperage) drawn by the processors to variate in the same pattern. Due to the low supply voltage values of modern processors, the load changes in amperage can be extreme. The processor could for example draw 6 A on low load, and 35 A current under maximum load, changing between these two values each millisecond. Certain components in the power supply or at the voltage control units for the processors will start to ring with the same frequencies due to the high load changes. For some computer models, these changes become audible.

If you don’t hear anything after switching to the “scale” feature, this will confirm that your computer is not affected by any oscillation problems in its voltage supply circuits. You may already hear some chirping noise after the application has been launched and the load is not 100%.

Such chirping noise can be annoying, but does not indicate an actual defect.