Windows 8 has a new feature called Storage Spaces, which is absent from Windows RT. The omission makes sense, as Storage Spaces is geared toward enterprise and power users. The feature lets you save files to two or more drives. If you run low on capacity, you can add more drives to a "storage pool" of drives. Pooled disks are connected via USB, SATA (Serial ATA), or SAS (Serial Attached SCSI). Microsoft uses a technology called "thin provisioning" to expand the storage capacity of physical disks beyond their stated size. A storage pool of two 2TB hard disks (4TB), for instance, becomes a 10TB mirrored space.