Starting in the late 1990s when hard disk capacities grew beyond several gigabytes, it became customary for the PC vendor to copy the entire Windows installation CD-ROM onto the hard disk in the c:\windows\options\cabs folder. Whenever you install new hardware or software and are prompted for the Windows "system" disk, select c:\windows\options\cabs first. If the .CAB files were stored there, you do not need the CD-ROM.