The HP 375870-B21 is an SAS (Serial Attached SCSI) which is a combination of SATA (a form of IDE or ATA) and SCSI. This allows the transfer rate for the 375870-B21 to reach a staggering 300 MB/s. This is also partly through the 15,000 rpm speed that the spindle achieves. The capacity for the HP 375870-B21 can reach a peak of up to 72 GB. SAS hard drives are available in either the 2.5” or 3.5” format, the 375870-B21 however has a 3.5” form factor that is common to all IDE hard drives. The HP 375870-B21 is compatible with and mainly used in servers, particularly HP ProLiant servers.