The Department of Computer Science provides each of its faculty, staff, and graduate students with backups of a specified amount of space (2 GB for faculty, 1 GB for staff and graduate students) on his or her desktop PC system; these backups are paid for through the department's Computer Services Recharge Center. The department also provides backups of additional PC disk space for research projects. Fees for this disk space are based on a four-year useful lifetime for the backup servers, beginning 1/1/2005 and ending 12/31/2008. The current rate is $30/gigabyte for four years of backups. Backups are available in one gigabyte increments only. The fee is prorated monthly for disk space obtained after 1/1/2005 and is also prorated for grants that end before 12/31/2004. For example, if a project whose grant ends on 12/31/2008 wants backups for 2 GB starting on 6/30/07, the charge is (1.5 years) X ($30/GB/4 years) X (2 GB) = $22.50.