Hard Disk Drive Interfaces

Hard disk drives provide access via a number of different bus types. These drives can either be attached directly to the motherboard, or via an additional controller board. The particular interface, determines the transfer speed available, and the typical application for which a drive is suited.

Early Hard Disk Drive Interfaces

The earliest PC hard disk drives, used the ST-506 interface developed by Seagate, which used Modified Frequency Modulation (MFM) encoding. This type of drive required a separate controller board plugged into the motherboard, allowing 5MB/s transfer speeds.

The ST-412 was the second generation of hard disk drive interface developed by Seagate, used Run Length Limited (RLL) encoding, providing an increase in speed, as well as microprocessor controlled stepper motor to increase seek times. Enhanced Small Disk Interface (ESDI) was developed by Maxtor, which saw some of the electronics moved onto the hard disk drive. These enhancements increased the speed possible to 20MB/s.

SCSI/SAS/Fibre Channel

The Small System Computer Interface (SCSI) developed by Shugart Associates, placed the electronics required to control the drive on the hard disk, although still required an additional host adaptor controller board. SCSI provides a method of connecting multiple drives and devices to a single host adaptor, via a common command interface. The earliest SCSI drives had transfer speeds of 5MB/s, but by 2003, this had increased to 640MB/s.

SCSI along with its successors Serial Attached SCSI (SAS) and Fibre Channel are now generally used in enterprise server applications. Fibre Channel allows up to 16Gbit/s transfer speed, as of 2014. Early SCSI disk drives were common in Apple Macintosh computers, but since replaced by ATA and then SATA interfaces.


Integrated Drive Electronics (IDE) developed by Western Digital evolved to become the Parallel ATA (PATA), originally AT Attachment interface, which was in large scale use since the late 1980’s, with the electronic fully independent of the host computer. Further enhancements saw the Extended IDE (EIDE) and Ultra ATA (UATA) interfaces, to keep pace with growing capacities, requiring changes to the ATA command set.

Direct Memory Access (DMA) was introduced, to increase the transfer speed, later replaced by Ultra DMA (UDMA) to allow transfer speeds of up to 133MB/s.


Serial ATA (SATA) was introduced in 2003, to supersede PATA, providing several advantages. The amount of cabling required was significantly reduced, which also allowing faster data transfer rates, through higher signalling rates. This is possible, as there is no requirement to synchronise a set of parallel communication lines, which were also susceptible to crosstalk and other interference.

July 2013 saw SATA speeds reach 600MB/s. The next revision of the specification defines an interface combining both SATA and PCI Express buses, and as of early 2015 is predicting speeds of 1969 MB/s.

Hard Disk Data Recovery

No matter which interface your hard disk drive uses, DiskEng have seen it before, have the procedures and expertise to perform a successful data recovery.

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