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.
