Hard Drive Glossary

SECTOR
A sector is a logical segment of information on a particular track, and is the smallest addressable unit of storage on a disk. Tracks are divided into sectors, with each sector 512 bytes long. They contain data, but also contain information as to where the data is located, among other useful bits of information. Modern drives use ZDR – Zone Density Recording, where there are more sectors per track on the outside of the disk where there is more surface area, and fewer and fewer sectors as you go in toward the center of the drive. Newer drives have about 16 zones now. This allows more data to fit on the drive. The outer zones therefore have a higher data transfer rate that those closer to the center of the drive.

SECONDARY (IDE) PORT
A “secondary” IDE port or interface is virtually identical to a “primary” IDE port or interface except it uses a different interrupt and I/O address to avoid collisions with the primary interface. A secondary interface allows you to connect another ribbon cable with two additional ATA devices (hard disk, ATAPI CD-ROM or ATAPI tape) for a total of four.

SECTOR ADDRESS TRANSLATION
Most drives manufactured within the last 3 years feature a universal translate mode. In an AT/EISA-class system, the drive may be configured to any specified combination of cylinders, heads and sectors within the range of the drive’s formatted capacity.

SECTOR PULSE SIGNAL
A digital signal pulse which indicates the beginning of a sector. Embedded servo pattern or other prerecorded information may be present on the disk when sector is active. Only present in hard sectored drives.

SEEK
A random access operation by the disk drive. The act of moving a set of read/write heads so that one of them is over the desired cylinder. The actuator or positioner moves the heads to the cylinder containing the desired track and sector.

SEEK COMPLETE SIGNAL
A digital signal level which indicates that the positioner is not moving and is located over a cylinder or offset position.

SEEK TIME
The elapsed time between the issuing of a step pulse or seek command and when the head settles onto the desired cylinder. This is sometimes is measured without settling times, or the time necessary for the head to settle over the specified cylinder.

SEQUENTIAL ACCESS
The writing or reading of data in a sequential order such as reading data blocks stored one after the other on magnetic tape. This is contrasted to random access of information.

SERVO BURST
A momentary servo pattern used in embedded servo control implementations usually positioned between sectors or at the end of a track.

SERVO CONTROL
A technique by which the speed or position of a moving device is forced into conformity with a desired or standard speed or position.

SERVO HEAD
A magnetic head designed for accurately reading (only) of servo information.

SERVO PATTERN
A read-back signal that indicates the position of a head relative to a track.

SERVO SURFACE
A recording surface in a multi-surface disk drive that only contains control information which provides timing, head position, and track-following information for the data surfaces.

SERVO SYSTEM
An automatic system for maintaining the read/write head on track; can be either “open loop”, “quasi-closed loop”, or “closed loop”.

SERVO TRACK
A track on a servo surface. The prerecorded reference track on the dedicated servo surface of a disk drive. All data track positions are compared to their corresponding servo track to determine “off track”/”on track” position.

SETTLING TIME
The time it takes a head to stop vibrating, within specified limits, after it reaches the desired cylinder.

SILICON
Semiconductor material generally used to manufacture microprocessors and other integrated circuit chips.

SMALL COMPUTER SYSTEM INTERFACE (SCSI)
An intelligent interface that incorporates controller functions directly into the drive. See the SCSI vs. IDE.

S.M.A.R.T. CAPABILITY
Self-Monitoring Analysis and Reporting Technology. Prediction of device degradation and/or faults.

SOFT ERROR
A data error which can be overcome by rereading the data or repositioning the head.

SOFT SECTORED
A technique where the controller determines the beginning of a sector by the reading of format information from the disk. This is contrasted to hard sectoring where a digital signal indicates the beginning of a sector on a track.

SOFTWARE
Applications programs, operating systems, and other programs as opposed to hardware.

SPINDLE
The rotating hub structure to which the disks are attached.

SPINDLE MOTOR
The motor that rotates the spindle and therefore the disks.

SPUTTERED MEDIA
Magnetic disk or tape that has the magnetic layer deposited by sputtering means.

START/STOP CYCLES
This indicates the minimum cycles for reliable start/stop function at a 60% confidence level.

STEPPER MOTOR
A motor that has known detent positions where the rotor will stop with the proper control in some cases. The digitally controlled motor moves the head positioner from track to track in small, step-like motions.

STORAGE CAPACITY
The amount of data that can be stored in a memory location, or on a disk drive. Usually specified in kilobytes for main memory and floppy drives and megabytes & gigabytes for mass storage devices. See Decimal vs. Digital for further details.

STORAGE DENSITY
Usually refers to recording density (BPI, TPI, or a combination of both.)

STORAGE LOCATION
A memory location, identified by an address where information may be read or written.

STROBE OFFSET SIGNAL
A group of digital input signal levels which cause the read PLL and/or data decoder to shift the decoding windows by fractional amounts. Often early/late are modified when two signals are used.

SUFFIX
A letters and/or numbers at the end of a model number of many hard drives. Many times this denotes the type of drive and the number of surfaces & heads.

SURFACE
Each platter (disk) has two surfaces, the top and bottom surface. Each surface has it’s own head for reading, writing & erasing data.