O&O SpeedCheck allows you to simulate your Windows system in a fragmented and defragmented state. As the application runs in a simulated state no data is written, rather it reads test data from the hard disk. On completion of the simulation you are shown a comparison of the two test times, and the possible increase in speed available to you. You can then see how much your PC may be accelerated by undertaking a system defragmentation.
O&O SpeedCheck runs in two phases: simulated reading of files that are fragmented, and simulated reading of the same files had they been defragmented. Files are read continuously one after the other on a hard disk level from the start of the partition. During this reading process, the test files are opened and read operations are carried out according to the number of fragments the files are split into. This simulates how Windows reads your system's fragmented files. The reading process of the defragmented files is done in one read operation and loaded into the memory.
The possible resulting increase in your system's speed is measured by comparing the respective total times for both runs. Both the test runs are carried out five times, in order to nullify, as far as possible, any side effects that are caused by the operating system and applications running in the background. It is recommended that you avoid running other applications during the test runs, as any file operations can lead to a distorted result.