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hard disk interfaces

Most hard disks use the Parallel ATA (PATA), Serial ATA (SATA) or SCSI interfaces. SCSI drives have traditionally been found on servers and high-performance workstations and were the first drives used in fault-tolerant RAID systems. Today, ATA drives are widely used for RAID arrays.

Following are the major types, including older ones for comparison. Most hard disks use the run length limited (RLL) encoding method; however, the encoding is not necessarily prescribed by the interface. See IDE, PATA, SATA, SCSI, RAID, RLL and hard disk.


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

 SATA/IDE  RLL    150-600   12TB

 PATA/IDE  RLL      3-133    1TB

 SCSI      RLL      5-320    1TB

 SAS       RLL    375-750   12TB

 Older Interfaces           Range

 IPI       RLL     10-25MB   200MB-3GB
 ESDI      RLL      1-3MB    80MB-2GB
 SMD       RLL      1-4MB   200MB-2GB
 IDE       RLL      1-8MB    40MB-1GB

 ST506 RLL RLL      937KB    30MB-200MB
 ST506     MFM      625KB     5MB-100MB

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 Berkely system above.

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