Glossary of Hard Disk Drive Terminology (Letter F)

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.

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Glossary of Hard Disk Drive Terminology (Letter E)

ECC On-the-Fly
A hardware correction technique that corrects errors in the read buffer prior to host transfer without any performance penalties. These error corrections are invisible to the host system because they do not require assistance from the drive’s firmware.

EIDE (Enhanced Integrated Drive Electronics)
The primary interface used by desktop PCs to handle communication between hard drives and the central processing unit. The equivalent interface system in most enterprise systems is SCSI.

Embedded Servo Control
The embedded servo control design generates accurate feedback information to the head position servo system without requiring a full data surface (which is required with a “dedicated” servo control method) because servo control data is stored on every surface.

Encoding
The process of modifying data patterns prior to writing them on the disk surface.

Enterprise
The series of computers employed largely in high-volume and multi-user environments such as servers or networking applications; may include single-user workstations required in demanding design, engineering and audio/visual applications.

Enterprise Storage Group
The Western Digital operation that designs, produces and markets hard drives for the enterprise market.

Error Correction Code (ECC)
A mathematical algorithm that detects and corrects errors in a data field.

Error Log
A record that contains error information.

Error Rate
The number of errors of a given type that occur when reading a specified number of bits.

Extended Partition
You can create multiple partitions on a hard disk, one primary partition and one or more extended partition(s). Operating system files must reside on the primary partition. An extended partition is a partition where non-system files (files other than DOS or operating system files) can be stored on a disk. You can also create logical drives on the extended partition.

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Glossary of Hard Disk Drive Terminology (Letter D)

Database
A collection of data stored on a computer system medium, such as a hard drive, CD-ROM, etc., that can be used for more than one purpose.

Data Lifeguard
A Western Digital exclusive data reliability feature that automatically detects, isolates and repairs problem areas on the hard drive before data loss can occur.

Data Synchronizer
An electronic circuit that uses a clock signal to synchronize data to facilitate interpretation.

Dedicated Landing Zone
The designated radial zone of the disk, usually at the inner portion of the disk, where the heads are stored to avoid contact with the data cylinders when power to the drive is off.

Defect Free
A term used to describe recording surfaces that have no detectable defects.

Defect Management
A general methodology of eliminating data errors on a recording surface by mapping out known defects on the media. The defective areas are rendered inaccessible, so that when information is written to the disk, it is stored to non-defective locations on the disk.

Desktop
A personal computer sized to fit on or under your desktop. Western Digital EIDE hard drives are designed to fit into a desktop PC.

Differential SCSI
An electrical signal configuration which uses pairs of lines for data transfer. Used primarily in applications requiring long cable lengths of up to 82 feet (25 meters).

Direct Memory Access (DMA)
A process for transferring data directly to and from main memory, without passing through the CPU. DMA improves speed and efficiency by allowing the system to continue CPU processing even while it is transferring data to/from the hard drive.

Disk
A rigid platter, usually constructed of aluminum or mylar, with a magnetic surface that allows the recording of data, that is stored inside the drive.

Disk Controller
The chip or circuit that controls the transfer of data between the disk and buffer. (See also disk drive controller and interface controller).

Disk Drive Controller
The hard disk drive controller electronics which include the disk controller and the interface controller. (See also disk controller and interface controller.)

Disk Operating System (DOS)
The computer program that controls the organization of data, files and processes on the computer.

Disk Transfer Rate
Speed at which data transfers to and from the disk media (actual disk platter); a function of the recording frequency. Typical units are bits per second (BPS), or bytes per second. Hard drives have an increasing range of disk transfer rates from the inner diameter to the outer diameter of the disk.

Distribution Channel
Electronics distributors and certain retail chains that deliver electronic goods to end users through value-added resellers and some retail stores.

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Glossary of Hard Disk Drive Terminology (Letter C)

Cable Select (CSEL)
An alternative option which can be used in place of setting Master/Slave jumpers in the designation of drives in a dual drive configuration. Master/Slave designation is based on the position of the drives relative to the cable. Special cabling is required by the system manufacturer to selectively ground the CSEL signal on one of the IDE cable connectors. For example, when one of the drives is connected to the grounded CSEL conductor, it configures itself as the Master. When the second drive is connected to the other connector, on which CSEL is not grounded, it becomes the slave. This eliminates the need for unique jumpering configurations between the Master and Slave drives.

Cache
High-speed RAM used as a buffer between the CPU and a hard drive. The cache retains recently accessed information to speed up subsequent accesses to the same data. When data is read from or written to disk, a copy is saved in the cache, along with the associated disk address. The cache monitors the addresses of subsequent read operations to see if the required data is already in the cache. If it is, the drive returns the data immediately. If it is not in the cache, then it is fetched from the disk and saved in the cache.

Capacity
The amount of information, measured in bytes, that can be stored on a hard drive. Also known as storage capacity.

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

Channel Assembly
In the computer industry, the final assembly of a system by a distributor or reseller from kits provided by the manufacturer and from components shipped directly to the assembler by subsystem makers.

Clean Room
An environmentally controlled, dust-free, assembly or repair facility in which hard drives are assembled or opened for internal servicing.

Cluster
A cluster is defined as an allocation unit. At least one cluster is allocated to each file, regardless of the file’s size, that is stored in the DOS environment. The cluster size increases with the partition size determined during formatting. With a 1024 MB partition, the cluster size is 32 KB. Each file stored consumes 32 KB of storage space, no matter how small the file. Create multiple, smaller partitions to avoid wasting space on small files. (This definition applies to FAT16).

CMOS Setup
A program supplied in most systems that allows you to configure internal and external devices.

Command Aging
A SCSI feature that prevents the command reordering algorithm from keeping I/O processes waiting in the command queue for extended periods of time.

Command Queuing
A feature that enables the drive to receive I/O processes from one or more initiators and execute them in an optimum sequence.

Command Reordering
A feature that allows the drive to reorder I/O processes in the command queue, which results in minimizing the seek time and rotational latency and thus increases throughput.

Controller
See disk controller, interface controller, and disk drive controller.

Controller Card
An adapter with the control electronics for one or more hard drives. Usually installed in a bus slot in the computer.

Correctable Error
An error that the drive can correct by using Error Detection and Correction schemes.

Customer Configuration Code (CCC)
A firmware revision tracking code that defines a major product change. This number increments as form, fit or function changes are implemented. The CCC code guarantees that the correct revision of drive product is provided to the customer.

Cyclic Redundancy Check (CRC)
Data stored or transmitted with data to detect corruption. By calculating the CRC data and comparing it to the original data sent, the receiver can detect some types of transmission errors.

Cylinder
The cylindrical surface formed by identical track numbers on vertically stacked disks.

Cylinder, Head, Sector (CHS) Addressing
A method of referencing the sectors on a drive as a collection of unique cylinder, head and sector addresses. Each block on the drive will have a unique cylinder, head and sector address.

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Glossary of Hard Disk Drive Terminology (Letter B)

Bandwidth
The amount of data that can be sent over a given circuit. See also buffer bandwidth.

BIOS (Basic input/output system)
A program or set of programs that control the basic functions of the computer.

Bit
An abbreviation for a binary digit which can be either 0 or 1. A bit is the basic data unit of all digital computers. It is usually part of a data byte, or data word; however, a single bit can be used to control or read logic ON/OFF functions. A bit is a single digit in a binary number. Bits are the basic unit of information capacity on a computer storage device. Eight bits equal one byte.

Bit density
Expressed as bits per inch (BPI), the number of bits that can be written onto one inch of track on a disk surface.

Block
A group of bytes handled, stored, and accessed as a logical data unit, such as an individual file record. A block in UNIX workstation environments is the smallest contiguous area that can be allocated for the storage of data. (Note: A different definition of the term is used when referring to the physical configuration of a hard drive.)

Boot
To start or restart your computer; loading the operating system.

BPI
Bits per inch. Indicates the density of information on a hard drive. See bit density.

Buffer
A temporary data storage area used to make up for a difference in data transfer rates and/or data processing rates between sender and receiver. For example, a printer buffer copies data from the computer and holds it until the printer is ready to print it.

Buffer Bandwidth
The speed of transferring data to or from the buffer.

Build-to-order
In the computer industry, the assembly of a system in response to a customer’s order, rather than for inventory or mass shipment. A system utilized by Dell Computer and Gateway, now being emulated to some degree by other PC makers like IBM, HP and Compaq.

Business Model
A company’s financial plan, including product pricing and margin calculations.

Burst Mode Transfer Rate
The transfer rate into the buffer RAM of the hard disk. This rate does not factor in delays due to latencies or host delays. See also transfer rate.

Bus
The path that carries data between the computer (microprocessor) and peripheral devices. An IDE interface cable and a SCSI cable are both examples of a bus.

Byte
A sequence of eight binary digits or bits regarded to be a unit or binary word. The storage capacity of a disk drive is commonly measured in megabytes, which is the total number of storable bits divided by eight million.

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Glossary of Hard Disk Drive Terminology (Letter A)

Access
Retrieval of data from or transfer of data into a storage device or area such as RAM or a register.

Access Time
The amount of time, including seek time, latency and controller time, needed for a storage device to retrieve information.

Active Partition
The partition of the drive that contains the operating system. If the drive has multiple partitions, only the primary partition can be made active. A hard drive can have only one active partition.

Active Termination
One or more voltage regulators that produce termination voltage. The voltage regulator(s) drive a constant voltage along the bus to ensure that the data signal stays constant and strong over the entire length of the bus. The result is increased data integrity and reliability.

Actuator
A mechanical assembly that positions the read/write head over the appropriate track.

Actuator Arm
The part of the actuator assembly that includes the positioning arm and the read/write heads.

Adaptive Caching
A feature of Western Digital drives that enables them to improve performance and throughput by adapting to the application being run.

Address
In the hard drive industry, there are several types of addresses; an address may refer to that of a drive, called a unit address; radial position, called a cylinder address; or circumferential position, referred to as a sector address.

AFR
Annualized Failure Rate.

Allocation
The method DOS uses to assign a specific area of the hard drive to a given file. (See also cluster.)

American National Standards Institute (ANSI)
A governmental body of the United States responsible for approving US standards in many areas, including computers and communications. ANSI is a member of the International Standards Organization (ISO).

Arbitrated Loop
Fibre channel topology where two or more ports can interconnect but only two ports can communicate at the same time.

Arbitration
The act of determining which command, device, or communication protocol controls the operating environment.

Areal Density
The number of bits of data that can be recorded onto the surface of a disk or platter usually measured in square inches. The areal density is calculated by multiplying the bit density (BPI – Bits Per Inch) by the track density (TPI – Tracks Per Inch).

ASP
Average selling price.

Asynchronous Transmission
Each byte of information is synchronized individually through the use of request and acknowledge signals.

AT Bus Attachment (ATA-4)
The interface defined by IBM for the original AT disk controller. Western Digital designed the WD Caviar® drives to be fully ATA-4 compatible.

Auto Defect Retirement
If the drive finds defective sectors during reads or writes, they are automatically mapped out and relocated.

Auto Park
Turning off the drive power causes the drive to move the read/write heads to a safe non-data landing zone and lock them in place.

Average Access Time
The average length of time a drive takes to perform seeks, usually measured with 1/3 stroke.

Average Seek Time
Length of time it takes the drive to move the read/write heads to a safe non-data landing zone and lock them in place.

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