An advance reservation is the mechanism by which Moab guarantees the availability of a set of resources at a particular time. Each reservation consists of three major components: (1) a set of resources, (2) a time frame, and (3) an access control list. It is a scheduler role to ensure that the access control list is not violated during the reservation's lifetime (that is, its time frame) on the resources listed. For example, a reservation may specify that node002 is reserved for user Tom on Friday. The scheduler is thus constrained to make certain that only Tom's jobs can use node002 at any time on Friday. Advance reservation technology enables many features including backfill, deadline based scheduling, QOS support, and grid scheduling.