Articles

Qualification
The process by which sample components are tested for their compatibility and utility as parts of a system. Western Digital OEM customers qualify WD hard drives for use in their computers.

Queue
A first-in-first-out (FIFO) data structure used to sequence multiple demands for a resource such as a printer, processor, or communications channel. The host adds objects to the end of the queue and takes them off the front.

Partition
A way to logically divide a hard drive so that an operating system treats each partition as a separate hard drive. Each partition has a unique drive letter.

Passive Termination
A termination architecture that is used to match the impedance at the end of the SCSI bus by using a voltage divider network of passive resistors.

PC
Personal computer.

Personal Storage Division
The Western Digital organization responsible for design, production and sale of hard drives for personal computers.

Platform
A basic design from which a series of products is engineered and produced. Western Digital’s new, 4.3 GB-per-platter platform, for example, is the basis for five products ranging in capacity from 4.3 to 13.0 gigabytes.

Platter
An actual metal (or other rigid material) disk that is mounted inside a fixed-disk drive. Many drives consist of multiple platters mounted on the spindle to provide more data storage surfaces. Each platter may use one or both surfaces to store data.

Port
A connection or socket on the motherboard or controller card. A motherboard may have one or two ports (primary and secondary). If your motherboard has only one port, you may need to add a controller card to create a secondary port.

Pre-fetch
Instructions that are loaded into a queue when the processor’s external bus is otherwise idle.

Primary Partition
The partition where the operating system files are stored. To start your operating system from a hard disk, it must have a primary partition. You must also make the primary partition active.

Product Road Map
A company’s plan for the introduction of new products.

Protocol
A convention of data transmission that defines timing, control format, and data representation.

PRML (Partial Response Maximum Likelihood)
A read channel using sampled data, active equalization and Veterbi detection to accurately retrieve the user data off the disk.

Programmed I/O
In a disk drive with an AT interface, data transfers between the drive and host using programmed I/O (PIO). The host uses PIO to write to the Command Block Registers (CBRs) when transmitting control information, such as the location of a read command.

Proximity Recording
A recording technology that increases recording density by allowing the read/write head to come in close proximity to the disk surface.

Operating System
Software that allows the user and programs installed on your system to communicate with computer hardware such as a hard drive.

Original Equipment Manufacturer (OEM)
In the case of Western Digital, OEM customers are companies such as Compaq, Gateway, IBM and Dell.

OEM content
The portion of a company’s output sold to OEM customers, expressed as a percent of total production.

Network Computer
A kind of computer that contains limited data storage capacity and is used to communicate with a central data storage facility such as a server or RAID system.

Magnetic flux
The pattern of magnetic pole directions of the bits written on the disk.

Manufacturing Yield
The portion of unit production of a manufacturing process that is usable, saleable product; usually expressed as a percent of total output of that product.

Master
The first drive in a dual drive combination. A master drive by itself (with no slave) is called a single drive.

Media
In hard drives, the disks and their magnetic coatings; sometimes refers to the coating material alone.

MB (Megabyte)
Western Digital defines a megabyte as 1,000,000 (one million) bytes.

Mechanical Latencies
Include both seek time and rotational latency. Mechanical latencies are the main hindrance to higher performance in hard drives. The time delays of mechanical latencies are one hundred times higher than electronic (non-mechanical) latencies associated with the transferring of data. See also Seek Time, Rotational Latency.

Memory
A device or storage system capable of storing and retrieving data.

MFM (Multiple Frequency Modulation)
A method of encoding analog signals into magnetic pulses or bits.

MR Heads (Magneto-resistive Heads)
MR heads were developed to increase areal density and improve drive performance. MR heads use separate read and write elements, as opposed to traditional inductive thin-film read-write heads. MR heads use an inductive element for writing data, and a separate magneto-resistive element for reading information. The read element has a magnetically sensitive material that detects data recorded on the magnetic disk surface. MR head construction results in a stronger signal than that produced by inductive thin-film read-write heads, which permits it to read higher areal density data. Since the magneto-resistive element can only read data, a conventional thin-film inductive element writes data to the disk.

MTBF (Mean Time Between Failures)
Average time (expressed in hours) that a component works without failure. It is calculated by dividing the total number of operating hours observed by the total number of failures. Also, the length of time a user may reasonably expect a device or system to work before an incapacitating fault occurs.

MTTR (Mean Time to Repair)
The average time it takes to repair a drive in the field. In the field, only major subassemblies are changed (the PCB, sealed housing, etc.), excluding component level repairs as these are not performed in the field.

Multi-media
A simultaneous presentation of data in more than one form, such as by means of both visual and audio.

Multi-user
In information technology, a system that enables more than one user to access data at the same time.

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.