If you are heavy user, eventually you will have low priority when competing with other users. We want to protect somebody who wants to come in and run 10 to 20 hours of computing time to have a better response time than someone who is running for months and months and months. Without access to scavenged computing cycles, Livny explains, many of the projects run on Condor would monopolize a single workstation for months, a luxury not many researchers can afford. One UW-Madison graduate student, for example, consumed in just one month the number of cycles a single workstation would generate running around the clock for 350 days. All the juggling Condor must do wastes time.
Projects move from computer to computer.
Projects often must wait their turn. Information must be moved in and out of electronic memory and the magnetic storage drives. Often, however, the guest project hasn't finished when Condor must yield the workstation. When it places a checkpoint, Condor remembers the current status of the program, as well as any results that had been computed so far. Then, when it restarts the project somewhere else, it can pick up at the checkpoint.