Glossary of PC terms: S

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S.M.A.R.T.	Self-Monitoring, Analysis, and Reporting Technology.  Presently, most ATA and SCSI drives use S.M.A.R.T. to predict failure and to protect data.  Not all failures can be predicted, but S.M.A.R.T. keeps evolving and getting better and better.
SCSI (Small Computer System Interface)	SCSI (pronounced as scuzzy) is the acronym for Small Computer System Interface, a high performance peripheral interface that can independently (on the PC) distribute data among peripherals. Unlike ATA, SCSI incorporates those instructions needed for communication with the host PC. Freeing the host computer from this job makes it more efficient in performing its user-oriented activities. SCSI is a specification for a peripheral bus and command set defined in an ANSI  standard X3.131-1986. For details go here.
Sector	A part of each track defined with magnetic marking and an ID number. Sectors have a sector header and error correction code (ECC). In modern drives, sectors are numbered sequentially.
Self-loading slider	see Air-bearing slider
Seek time	The average time required for a magnetic or optical head to move to a new track.
Servo (mark, mechanism)	A feed-back positioning system embedded in the platters and needed to help the magnetic head to evaluate its current position.
Settling time	The time required for the servo system to lock onto the new track
Shock resistance	An ability of a drive to withstand impact-like acceleration. Measured in G units.
Signal-to-noise ratio	(SNR) the ratio of the signal power to the noise power in the data channel, measured in dB.
Sleep mode	A power saving option when the hard drive is powered down (spindle rotation is stopped and the heads are parked on the landing zone or on the ramp) after a pre-set period of time. Most often used in mobile computers.
Slider	A micro-fabricated part of the magnetic drive that carries read/write elements. See also Air-bearing slider
Start of Frame (SOF)	The first transaction in each frame.  SOF allows endpoints to identify the start of frame and synchronizes internal endpoint clocks to the host.
Stage	One part of the sequence of a control transfer, i.e., the setup stage, data stage, and status stage.
Stepper motor actuator	An actuator using a stepper motor that moves one step at a time. Was used in older hard drives before being replace by the Voice Coil Actuator.
Storage capacity	The formatted capacity of a drive.
Stiction	A phenomenon caused by the surface tension of liquids. The liquid in between two solid surfaces tends to retain the smallest surface area and pulls these solid surfaces together.  This effect is noticeable for very smooth surfaces only. The generated forces could be extremely high and, in the case of magnetic hard disk drive, could prevent a disk from rotating when the slider sticks to a very smooth disk surface.
Synchronous data transfer	Data sent with the clock pulse defining the intervals between bits, as opposed to asynchronous data transfer. See also isochronous data transfer.
Super-paramagnetic limit	A limit of density of magnetic recording due to the fact, that at the very high recording density, the magnetic bits become so small that they can not keep residual magnetization for any practically useful amount of time. Predicted to occur at about 100 Gb/inch squared.
Suspension	See Head suspension

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