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Definition: hard disk interfaces


Today's hard drives use SATA or SAS interfaces, which are the serial versions of their PATA and SCSI predecessors. SATA drives are found in most personal computers unless they use solid state drives (SSDs), in which case the NVMe interface is an option (see NVMe). Enterprise-class SAS drives are found in servers and high-end workstations.

Following are the major types, including older ones for comparison. Although drives use the run length limited (RLL) encoding, the encoding method is not prescribed by the interface. See SATA, serial attached SCSI, RAID, RLL and hard disk.

 HARD DISK INTERFACES

               Transfer Rate
                   (MB per   Max.
 Type   Encoding**   sec)  Storage

 SATA       RLL    150-600   20TB

 SAS        RLL    375-750   12TB

 Older Interfaces

 PATA       RLL      3-133    1TB

 SCSI       RLL      5-320    1TB

 IPI        RLL     10-25MB   3GB
 ESDI       RLL      1-3MB    2GB
 SMD        RLL      1-4MB    2GB

 ST506 RLL  RLL      937KB   200MB
 ST506 MFM  MFM      625KB     5MB





The First RAID System
Using SCSI disks, this prototype was built by University of Berkeley graduate students in 1992. Housing 36 320MB disk drives, the total storage of this entire rack was a whopping 11GB. See RAID. (Image courtesy of The Computer History Museum.)






Twenty Five Years Later
In 2017, this single 10TB hard drive had 900 times as much storage as the 36 drives in the Berkeley system above.





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