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Landing Zone
The heads move to this location on the inner portion of the disk when commanded, or when the power has been turned off. User data is not stored in this area of the disk.

Laser Textured Media
Laser textured disks minimize the wear and friction on a hard drive. The precision and consistency of the laser zone texturing process is a contributor to the robustness of our Western Digital hard drives.

Latency
The period of time that the read/write heads wait for the disk to rotate to the correct position to access the desired data. For a disk rotating at 5200 RPM, the average latency is 5.8 milliseconds; or, the average time delay between the head arriving on track and the data rotating to the head. (Calculated as one-half the revolution period.)

Local Area Network (LAN)
A system in which computer users in the same company or organization are linked to each other and often to centrally-stored collections of data in LAN servers.

Logical Address
A storage location address that may not describe the physical location; instead, it used as a means to request information from a controller. The controller converts the request from a logical to a physical address that is able to retrieve the data from an actual physical location on the storage device.

LBA (Logical Block Addressing)
A method of addressing the sectors on a drive. Addresses the sectors on the drive as a single group of logical block numbers instead of cylinder, head and sector addresses. It allows for accessing larger drives than is normally possible with CHS addressing.

Logical Drive
A logical drive is a section of the hard disk that appears to be a separate drive in a directory structure. You create logical drives on the extended partition of a hard disk. While 26 letters exist for logical drives, the first three are reserved. A and B are reserved for floppy disk drives, and C is reserved for the first primary DOS partition. Therefore, you can create up to 23 logical drives on your extended partition. Logical drives are usually used to group directories and files.

Logistics Model
The systems by which a company organizes the physical distribution of its products. A hard drive manufacturer’s model might include portions to OEM customers, to distributors, to retail chains or to all of these.

Low-level formatting
The process of creating sectors on the disk surface; this permits the operating system to use the regions needed to create the file structure. Also called initialization. Low-level formatting is performed at the Western Digital factory. There is no need for you to low-level format a Western Digital drive.

Low profile (LP)
Standard 3.5-inch hard drives are available in heights of 1.0-inch and 1.6-inches. Low-profile hard drives measure 1.0-inches in height.

Kilobyte (KB)
Usually, this is a unit of 1000 bytes. In the case of computer memory, which is partitioned into sizes that are a power of two, a kilobyte is equal to 2 10 or 1024 bytes.

Jumper
In EIDE drives, a jumper is an electrically-conductive component that you place over pairs of pins that extend from the circuit board on the hard drive jumper block to connect them electronically. For example, a jumper is one way to designate a hard drive as master or slave. The jumper block is located next to the 40-pin connector on the hard drive.

Just-in-time (JIT)
A production and inventory control process in which components and materials are delivered to an assembly point as needed. This process is used in Western Digital manufacturing facilities and in most of the company’s customer plants.

IDE (Integrated Drive Electronics)
A type of drive where the interface controller electronics are incorporated into the design of the hard drive rather than as a separate controller.

Index Pulse Signal
A digital pulse signal indicating the beginning of a disk revolution. An embedded servo pattern or other prerecorded information is present on the disk following index.

Initiator
A device in control of the SCSI bus that sends commands to a target. Most SCSI devices have a fixed role as an initiator or a target; however, some devices can assume both roles.

Initialization
See low-level formatting.

Input
The incoming data that the computer processes, such as commands issued by the user.

Input/output (I/O)
An operation or device that allows input and output.

Interface
A hardware or software protocol that handles the exchange of data between the device and the computer; the most common ones are AT (also known as IDE) and SCSI. (See AT and SCSI.)

Interface controller
The chip or circuit that translates computer data and commands into a form suitable for use by the hard drive and controls the transfer of data between the buffer and the host. (See disk controller and disk drive controller.)

Interleave
The arrangement of sectors on a track.

Interrupt
A signal sent by a subsystem to the CPU that signifies a process has either completed or could not be completed.

ISA
Industry Standard Architecture. The standard 16-bit AT bus designed by IBM for the PC/AT system. ISA was the only industry standard bus for PCs until the recent release of MCA (MicroChannel Architecture), EISA (Extended Industry Standard Architecture), and PCI (Peripheral Component Interconnect).

Half-Duplex
A communications protocol that permits transmission in both directions but in only one direction at a time.

Half-height Drives
Standard 3.5-inch hard drives are available in heights of 1.0-inch and 1.6-inches. Half-height drives measure 1.6-inches in height.

Hard Drive
An electromechanical device used for information storage and retrieval, incorporating one or more rotating disks on which data is recorded, stored and read magnetically. Western Digital’s principal product.

Hard Drive Industry
The combined manufacturers of hard drives. In the United States, the industry is led by IBM, Maxtor, Seagate, Quantum and Western Digital.

Hard Error
An error that is repeatable every time the same area on a disk is accessed.

Hard Sectored
A technique that uses a digital signal to indicate the beginning of a sector on a track.

Head
The minute electromagnetic coil and metal pole which write and read back magnetic patterns on the disk. Also known as a read/write head. A drive with several disk surfaces or platters will have a separate head for each data surface. See also MR Head.

Head Actuator
A motor that moves the head stack assembly in a hard drive to align read/write heads with magnetic tracks on the disks.

Head Crash
Refers to the damage incurred to a read/write head when the head comes into contact with the disk surface. A head crash might be caused by severe shock, dust, fingerprints, or smoke, and can cause damage to the surface of the disk and/or the head.

Head Disk Assembly (HDA)
The mechanical components of a hard drive, including the disks, heads, spindle motor and actuator.

Head Loading Zone
An area on the disk specifically reserved for the heads to use when taking off or landing when power to the drive is turned on or off. No data storage occurs in the head loading zone.

Head Stack Assembly
The electromechanical mechanism containing read/write heads and their supporting devices.

Headerless Format
The lack of a header or ID fields (track format). This enables greater format efficiency and increased user capacity.

High-end Market
The enterprise market.

High-Level Format
A high-level format must be performed (with EZ-Drive or the Format command) on your new Western Digital hard drive before you can use it. Formatting erases all the information on a hard drive and it sets up the file system needed for storing and retrieving files.

Host
The computer that other computers and peripherals connect to. See also initiator.

Host Adapter
A plug-in board that acts as the interface between a computer system bus and the disk drive.

Host Interface
The point at which the host and the drive are connected to each other.

Host Transfer Rate
Speed at which the host computer can transfer data across the SCSI interface; or, the speed at which the host computer can transfer data across the EIDE interface. Processor Input/Output (PIO) modes and Direct Memory Access (DMA) modes are defined in the ATA-4 industry specifications for the EIDE interface.

GB (Gigabyte)
Western Digital defines a gigabyte as 1,000,000,000 (one billion) bytes or 1000 (one thousand) Megabytes.

Giant MR (GMR)
An advanced form of magnetoresistive head technology in which IBM is believed to hold the greatest product advancements.

FAT (File Allocation Table)
A data table stored at the beginning of each partition on the disk that is used by the operating system to determine which sectors are allocated to each file and in what order.

Fdisk
A software utility used to partition a hard drive. This utility is included with DOS and Windows 95 operating systems.

Fetch
The process of retrieving data.

Fibre Channel (FC)
The general name given to an integrated set of standards being developed by an ANSI-approved X3 group. This set of standards defines new protocols for flexible information transfer. Fibre channel supports three topologies: point-to-point, arbitrated loop, and fabric.

Fibre Channel Arbitrated Loop (FC-AL)
A subset of fibre channel network systems interconnection. A serial storage interface designed to meet the needs of high-end applications.

Fiscal Periods
Three-month segments of a fiscal year. Western Digital, with a June 30 fiscal year, has fiscal quarters ending on the last days of September, December, March and June.

Firmware
Permanent instructions and data programmed directly into the circuitry of read-onlymemory for controlling the operation of the computer.

FIT (Functional Integrity Testing)
A suite of tests Western Digital performs on all its drive products to ensure compatibility with different hosts, operating systems, adapters, application programs, and peripherals. This testing must be performed before the product can be released to manufacturing.

Flow Control
In PIO transfers, the ability of an EIDE drive to control the speed at which the host transfers data to or from the drive by using the IORDY signal. The host temporarily stops transferring data whenever the drive deasserts the IORDY signal. When the drive reasserts the IORDY signal, the host continues the data transfer.

Format
A process that prepares a hard drive to store data. Low-level formatting sets up the locations of sectors so user data can be stored in them. Western Digital hard drives are low-level formatted at the factory and therefore do not need to be low-level formatted by the end user. You need to perform a high-level format (with EZ-Drive or the Format command) on your new Western Digital hard drive before you can use it. Formatting erases all the information on a hard drive and it sets up the file system needed for storing and retrieving files.

Formatted Capacity
The actual capacity available to store data in a mass storage device. The formatted capacity is the gross capacity minus the capacity taken up by the overhead data required for formatting the media.

Form Factor
The industry standard that defines the physical and external dimensions of a particular device.

Full-Duplex
A communication protocol that permits simultaneous transmission in both directions.