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OEM
Original Equipment Manufacturer

Operating System
Software program that facilitates communication between the computer and its user

Outside Diameter
Largest radius track on a platter

Parity
a data error detection method, that ensures that the number of binary digits in a bit is always odd, so that accurate transmission of data can be checked by counting the number of bits for an odd parity

Partitioning
division of the area on the platter and allocating sections each of which becomes a logical device, so that the File Allocation Table (FAT) can deal with when in use

Parallel Port
PC peripherals are commonly connected to a PC via the parallel port

PCB
Printed Circuit Board, board that has the HDD chips attached to it

PCI
Peripheral Component Interconnect

Periphera
components usually attached to a computer systems CPU by controllers and cables

Plated Media
platters whose surface is plated with metallic alloy , allowing the disc to store more data than on iron-oxide plated discs

Platter
the magnetic disc that is part of a disk drive, the part of the HDD on which the data is stored

POH
Power on Hours

PnP
Plug and Play, the ability for users to plug in new devices into their existing system and immediately be able to use it, as a result of a group of leading hardware manufacturers (initiated by Microsoft), who have configured their hardware so that it automatically identified and configures peripheral devices

PRML
Partial-response maximum likelihood. Data is stored on hard drives as a tiny area of magnetism for each bit. As more and more data is squeezed on a disk, the magnetic areas become closer and closer and may affect one another. PMRL is a set of steps applied to data read from the disk. It removes probable errors and produces valid data from the tightly packed bits. PMRL allows an increase of up toe 30 % in the density of data on the disk

JPEG
Joint Pictures Expert Group. Compression method for still images

Jumper
connector box that can be placed over pins that protrude from the circuit board. The jumper can be changed to configure the HDD according to the system requirement

KB
Kilobyte, a measuring unit, 1 KB is 1,024 bytes

Landing Zone
(see head landing zone)

Latency
(see rotational latency)

LBA
Logical Block Address, a set of 28 bits, used by the E-IDE interface system, representing the capacity of the hard disk drive. These 28 bits can theoretically support a drive capacity of up to nearly 137 GB, but in practice DOS Limits this to 8.4GB

Low Level Formatting
The process of creating sectors on the media so that a drive can store information

Main Memory
(see head landing zone)

MB
Megabyte, unit of measure of bytes

Media (Magnetic)
the magnetic area on the platter, the area where the data is stored inside the hard disk

MFM
Modified Frequency Modulation, method of recording data on media using a recording code that is recognised by a specific and dedicated Hard Disk Controller (an encoding method to record data on a magnetic data carrier with twice the data density of FM)

MPEG (Motion Pictures Expert Group)
A compression method for full motion video, MPEG files are smaller than uncompressed video files

MR
Magneto-resistive. This describes materials whose electrical resistance changes when they are exposed to magnetic fields. Since hard drives store data as tiny spots of magnetism, it is possible to use magneto-restive heads to read the stored data. MR heads can be produced very small, allowing the circular disk tracks to be squeezed closer together ? thus increasing the capacity of the disk

MR head
Magnetic Recording head

MTBF
Mean Time Before Failure, rating indicating the expected number of power on hours (POH) before failure will occur

Gigabyte (GB)
1 Gigabyte = 1,073,741,824 digital bytes / 1,000,000,000 decimal bytes, a unit of measure for data

Hard Error
a data error which is not able to be overcome when the disk is reread, it occurs repeatedly at the same location on the media, indicating a defect in the surface

Hardware
computer equipment (as opposed to the computer programs and software)

HC
High-speed CMOS)

HDA
Head Disk Assembly

HDD
Hard Disk Drive, magnetic storage device

Head crash
Occurs when a head and disk accidentally touch, thereby damages the media (and subsequently the data)

Head Landing Zone
Area on the media which is dedicated to head takeoff and landing, no data is recorded in this area

Head positioner
(see Actuator)

Host
the computer system that the drive is integrated into

Hot swap
replacement of hard drives, whilst computer is in operation with zero downtime

Host adapter
a plug-in board or circuitry on the motherboard that acts as the interface between a computer system bus and the disk drive

IC
Integrated Circuits. IC’s are arrays of electronic components such as transistors, diodes, resistors built from a single piece of semiconductor material. Huge numbers of components (millions) can be placed upon a single chip, the external connections being made via the pins on the IC package

IDE
Integrated Drive Electronics, a hardware interface that allows peripheral devices to be attached to a PC

IDE Controller
The controller translates commands from the computer into something that the hard drive understands

Interface
transmitters/receivers that establish links between various parts of a computer and facilitate the exchange of data between these components (e.g. IDE, EIDE, SCSI, and for notebooks PCMCIA). The way the drive and host communicate with each other. It is a standard defined by industry organisations

Interleave factor
the number of sectors that pass beneath the heads before the next sector arrives (a means to optimise performance of a drive)

Internal Transfer rate
the speed at which data is transferred to and from the media, reflected in millions of bits per second (Mbits/second)

Inside Diameter
smallest radius recording track on a platter

Inside Diameter
smallest radius recording track on a platter

I/O
Input/Output

ISA
Industry Standard Architecture

ISO

International Standards Organisation, sets standards for computer industry

ISO-9660
a data format designed by the ISO in 1984

E Block
component that connects the actuator to the head/slider assemblies

ECC
Error Correction Code, detects and correct errors in a data field

Effective Seek Time
The time it takes to seek data, when all/part of the data needed is already stored in the buffer of the drive (speeds up the process)

EIDE (also ATA)
Enhanced Integrated Device Electronics, interface

Embedded Servo
Servo data that is embedded on the media. Allows the actuator to fine-tune the position of the head(s). It is a positioning signal that keeps the read/write heads positioned over the data. The advantage of an embedded servo is that the data can flow without interruptions making the drive suitable for multimedia and AV applications

ESD
Electro-static discharge

FAT
File Allocation Table

FCI
Flux Changes per Inch of data track, equals BPI

Firmware
permanent instructions and data programmed directly into the circuitry of read-only memory (cannot be erased) for controlling the operation of the computer or disk drive

Flux change
reflects the point where the direction of magnetisation reverses in order to define a binary digit (0 or 1)

Format
The arrangement of a magnetic track pattern on the media. This enables the drive to store user data, and is never altered (see also low level formatting)

Form factor
industry standard that defines the dimensions of a particular device (e.g. 5.25″, 3.5″, 2.5″)

Flying Height
the height at which the head moves over the media, a lower height, equals larger areal density