The OS and Programs can be on the same drive because once you are up and running, most of what the OS and the application needs will be memory-resident (assuming you have sufficient).
However, if the application is going to read from file A, write to file B, read from file A, write to file B etc., repetitively for many video frames, you’d best have file A and file B reside on two different drives, because if the two files are on the same drive, the heads have to constantly move back and forth, and head movement is time consuming.
I use Premiere Pro CS4 and often wondered why Adobe doesn’t have a chart showing a fewhead movement scenarios and suggesting drive allocations for optimum performance. (With their new Mercury engine, will it still matter any more?)
