Glossary
REMOVABLE DISK – Generally said of disk drives where the disk itself is meant to be removed, and in particular of hard disks using disks mounted in cartridges. Their advantage is that multiple disks can be used to increase the amount of stored material, and that once removed, the disk can be stored away to prevent unauthorized use.
RLL – Run Length Limited. A method used on some hard disks to encode data into magnetic pulses. RLL requires more processing, but stores almost 50% more data per disk than the MFM method.
ROM – Acronym for read only memory. Usually in the form of an ROM in the controller that contains programs that can be accessed and read but not modified by the system.
ROTARY ACTUATOR – The rotary actuator replaces the stepper motor used in the past by many hard disk manufacturers. The rotary actuator is perfectly balanced and rotates around a single pivot point. It allows
ROTATIONAL LATENCY – The delay between when the controller starts looking for a specific block of data on a track and when that block rotates around to where it can be read by the read/write head. On the average, it is half of the time needed for a full rotation (about 8 ms.).
S
SCSI – Acronym for Small Computer System Interface, an American National Standards Institute (ANSI) version of Shugart Associates' SASI interface between the computer and controller. SCSI has grown in popularity and is one of the most flexible and intelligent interfaces available.
SECTOR – A section of space along a track on the disk, or the data that is stored in that section. Hard disks most often have sectors that are 512 data bytes long plus several bytes overhead for error correcting codes. Each sector is preceded by ID data known as a header, which cannot be overwritten.
SEEK – A movement of the disk read/write head in or out to a specific track.
SERVO DATA – Magnetic markings written on the media that guide the read/write heads to the proper position.
SERVO SURFACE – A separate surface containing only positioning and disk timing information but no data.
SETTLE TIME – The interval between when a track to track movement of the head stops, and when the residual vibration and movement dies down to a level sufficient for reliable reading or writing.
SHOCK RATING – A rating (expressed in Gs) of how much shock a disk drive can sustain without damage.
SOFT ERROR – An error in reading data from the disk that does not recur if the same data is reread. Often caused by power fluctuations or noise spikes.
SOFT SECTORED – Disks that mark the beginning of each sector of data within a track by a magnetic pattern.
SPINDLE – The center shaft of the disk upon which the drive’s platters are mounted.
SPUTTER – A type of coating process used to apply the magnetic coating to some
STEPPER – A type of motor that moves in discrete amounts for each input electrical pulse. Stepper motors used to be widely used for read/write head positioner, since they can be geared to move the head one track per step. Stepper motors are not as fast or reliable as the rotary voice coil actuators which Maxtor disk drives use.