There is some confusion between 100% duty cycle and 100% CPU load. The duty cycle setting in BurnInTest determines how quickly the various tests in BurnInTest run. Using a duty cycle value of less than 100% means short pauses are inserted into the test. 100% means a tight testing loop, with no pause. The duty cycle value does not necessarily equal the percentage load value displayed in Windows task manager. It might seem like a good idea to run all the tests at the same time and wind up all the tests to 100% duty cycle. But it isn't.
Imagine you have one application running on a computer that uses 100% of the CPU time. Adding a second instance of the same application (which could also potentially use 100% of the CPU time as well) doesn't increase the load on the machine. You can't have 200% CPU load. It's impossible. So by running more tasks, you aren't increasing the load, instead the operating system puts more and more tasks into a sleep state as part of pre-emptive multitasking. Eventually none of the tasks get any work done as the execution time per task becomes less and less as you add more tasks. Most of the tasks are asleep for most of the time. It is the same with BurnInTest. You can have near 100% hardware load with duty cycle settings in BurnInTest of less than 100%.
So if 100% duty cycle for all tests isn't the best, then what is? The best duty cycle setting to achieve 100% load your hardware depends on your hardware and your testing goals.
But typuical settings might be something like,
Disk 100% duty cycle
3D 100% duty cycle
RAM 80% duty cycle
CPU 80% duty cycle (as the RAM, disk and 3D tests also use the CPU, the actual CPU load might still be 100%, depending on your hardware)
What tests you select to run and the ideal duty cycle settings will vary depending on your testing requirements and the hardware in use. In most cases it is common sense. Some examples;
Head back to the BurnInTest FAQ page.