Hard Drive Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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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.
Sectors

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.
 

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THIN-FILM HEAD
A magnetic transducer manufactured by the depositing of magnetic and electrical materials on a base material contrasted with prior art mechanical methods. Read/write heads whose read/write element is deposited using integrated circuit techniques rather than being manually wound.

THIN-FILM MEDIA
See plated thin film media.

TRACK
One surface of a cylinder. A path which contains reproducible information left on a magnetic medium by recording means energized from a single channel.

TRACK-FOLLOWING SERVO
A closed-loop positioner control system that continuously corrects the position of the disk drive's heads by utilizing a reference track and a feedback loop in the head positioning system. (See also closed loop.)

TRACKS PER INCH (TPI)
A measurement of radial density. Tracks per inch of disk radius.

TRACK POSITIONING
The method, both mechanical and electrical, used to position the heads over the correct cylinder in a disk drive system.
 

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ULTRA ADVANCED TECHNOLOGY ATTACHMENT (ULTRA-ATA)
The latest improvement of the AT-Attachment device interface. Also known as ATA/ATAPI-4, Ultra-DMA, Ultra-ATA, among other names, the interface has a theoretical maximum data transfer rate of 33MB/sec. See the Ultra DMA FAQ for more detailed information.

ULTRA DIRECT MEMORY ACCESS (ULTRA-DMA)
The latest improvement of the EIDE device interface. Also known as ATA/ATAPI-5, Ultra-ATA, or Ultra-DMA/100, this is the latest advancement to the ATA specifications: ATA/ATAPI-5. Which, among other improvements, supports Ultra DMA. This interface has a theoretical maximum data transfer rate (burst, not sustained) of 100MB/sec.

Ultra-DMA doubles the maximum transfer speed of the ATA-3 standard. Compare the Ultra DMA maximum burst transfer rates with the old ATA standards above.

Ultra DMA/100 achieves nearly six times the transfer rate of the existing PIO/ATA interface while not increasing the cycle time of the ATA bus clock over the rate currently used for PIO Mode 4.

This is achieved by:

  1. Improving timing windows in the protocol on the ATA bus;
  2. Reducing propagation delays by pipelining data transfers;
  3. Transferring data in synchronous (strobed) mode;
In addition, Ultra DMA/33/66/100 improves data integrity by using a Cyclic Redundancy Check (CRC) to flag any data transfer errors that may be made over the ATA bus (Note: In this application CRC is only used to improve data integrity for ATA bus transfers. It is not used to improve the data integrity of disk drives or host systems).

Although Ultra DMA/33 requires no physical change to the cable, receivers, or drivers of the ATA bus, Ultra DMA66/100 require a special 80 wire ribbon cable. On the other hand, Ultra DMA/33/66/100 protocols and commands have been designed to be compatible with existing ATA devices and systems. While new Ultra DMA/33/66/100 devices will be backwards compatible with most older (non Ultra DMA/33/66/100) systems, older ATA-1/2/3 devices will only be forward compatible with systems that have Ultra DMA/33 capability.

UN-CORRECTABLE ERROR
An error that is not able to be overcome with Error Detection and Correction.

UNFORMATTED CAPACITY
Storage capacity of disk drive prior to formatting, also referred to as the drives gross capacity. (See format.) The raw capacity of a drive, without allowance for loss due to storage of the format control information on the disk surfaces.

UNRECOVERABLE ERROR
A read error that falls outside the ability of a ECC mechanism to correct it, or the inability to overcome the error by rereading the data in question, with or without repositioning the head.
 

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VOICE COIL MOTOR
A positioning motor that uses the same principle as a voice coil in a loudspeaker. The motor has no detent positions. The mechanical motion output of it can be either rotary or linear.
 
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WHITNEY HEAD
A successor to the original Winchester read/write head design, the primary change was to make the flexure smaller and more rigid. This was first used in the IBM 3370/3380.

WHITNEY TECHNOLOGY
A method of constructing a read/write head in a rigid disk drive using a Whitney head. In all other details it is the same as Winchester technology.

WINCHESTER DRIVE
Originally meant to signify that the drive used Winchester technology, but many times it is used to mean it is a fixed disk drive, implementing either Winchester or Whitney technology and non-removable disks sealed in a contaminant-free housing.

WINCHESTER HEAD
The read/write head used in Winchester technology, non-removable media disk drives. May be either a monolithic or composite type. It is aerodynamically designed to fly within micro-inches of the disk surface.

WINCHESTER TECHNOLOGY
A method of constructing a rigid disk drive using concepts introduced in the IBM model 3340 disk drive. The primary changes from prior art technology was to lower the mass of the slider, use of a monolithic slider, radically changing the design of the flexure and having the slider come to rest on a lubricated disk surface when disk rotation ceases. In addition to the above, a totally sealed chamber containing the read/write heads and disks was used to protect against contamination.

WINDOW MARGIN
The amount of tolerance a read/write system has for Transition Jitter at a specified error rate level.

WORD
A number of bits, typically a multiple of eight, processed in parallel (in a single operation). Standard word lengths are 8, 16, 32, and 64 bits (1, 2, 4, or 8 bytes).

WRITE
The recording of flux reversals on a magnetic media.

WRITE PRE-COMPENSATION OR WPC
The intentional time shifting of write data to offset the effects of bit shift in magnetic recording. This is technology that was used on old MFM and RLL drives but is not needed with IDE drives. While this setting is usually set to 0, some systems, with "Auto Detect", set this to 65.535, however, it doesn't matter as the system ignores the setting anyway.

WRITE GATE SIGNAL
A digital input signal level which causes the drive circuitry to record data.
 

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ZONE DENSITY RECORDING (ZDR)
The disk capacity is increased with bit density management - common with Zone Density Recording. Each disk surface is divided into 16 circumferential zones. All tracks within a given zone contain a constant number of data sectors. The number of sectors per track varies in different zones; the outermost zone contains the largest number of data sectors and the innermost contains the fewest.
Zone Density Recording


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