Rebit Backup Software for Multiple PCs (6) RSCD350000MPOS CD-ROM disk drive 300 MB available hard disk space An available USB 2.0 port External USB 2.0 hard disk drive of equal or greater capacity than the internal system hard disk drives Compatible with 32-bit or 64-bit Windows XP and XP Pro (Service Pack 2 or Service Pack 3), and 32-bit or 64-bit Windows Vista