BackupPC uses a combination of hard links and compression to reduce the total disk space used for files. At the first full backup, all files are transferred to the backend, optionally compressed, and then compared. Files that are identical are hard linked, which uses only one additional directory entry. The upshot is that an astute system administrator could potentially back up ten Windows XP laptops with 10 GB of data each, and if 8 GB is repeated on each machine (Office and Windows binary files) would look like 100 GB is needed, but only 28 GB (10 × 2 GB + 8 GB) would be used. Compression of the data on the back-end will further reduce that requirement.