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Term
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Description
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Access
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The proccess by which data is being written from, or placed into, RAM, a register, or some data storage device.
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Access Time
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The interval between the time of issuing of an access command for a drive and the instant at which the target data may be read or written. In general, access time includes seek time, latency and controller overhead time.
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Actuator
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This is the moving arm holding the Read/Write disk heads. It can position them accurately over the platter surfaces via feedback from the servo system. The actuator is powered by a rotary voice coil.
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Address
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A number (usually in binary form) distinguishing a specific member of an ordered set of numbers (locations). In the case of hard disks, the address may consist of drives (unit address, for example for SCSI disks), radial positions (cylinder address), or circumferential position (sector address).
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Allocation
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The assignment of designated areas of a disk to particular data (files).
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Alternate Track
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Usually used for defect management, it designates a spare track on a disk used in case that a normal track becomes damaged or in general is rendered unusable.
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Analog
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A signal or a respective system that uses infinite states to convey information. A signal's value may be anyone belonging to a range of finite or infinite continuous interval of states (values). In contrast, digital signals can only have two states.
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Annualized Avearge Failure Rate (AFR)
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Applies to the period prior to the expiration of component design life, and is based on failures chargeable to a particular disk manufacturer. (Provided he implements such a policy.)
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ANSI
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American National Standards Institute.
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Apple-ATA
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Apple's implementation of the ATA interface. It is a subset of the ATA interface specification, ANSI proposal X3T9.2/90-143. Revision 3.1. This particular specification subset requires the IDE drive to support LBA (Large Block Area) mode.
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APplication Program (APP)
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A sequence of instructions determining how a computer should perform a task.
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Areal density
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A number defined as the multiplication of bit density (Bits Per Inch) by track density (Tracks Per Inch) or bits per square inch.
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ASCII
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American Standard Code for Information Interchange, pronounced "ask-ee". A binary code for data storage and exchange, used in communications and computers. ASCII is a 7-bit code providing 128 character combinations, the first 32 of which are control characters. Since the commonly used storage unit is an 8-bit byte [256 combinations] and ASCII uses only 7 bits, the extra bit is used differently depending on the computer and software/operating system. For example, the MS PC systems use the additional values for foreign language and graphics symbols. In the case of MacIntosh, the additional values can be user-defined.
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Asymmetry
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In the case of hard disks it means an anisotropy (distortion) of the readback analog signal which is shown in different intervals when comparing the positive and negative voltage peaks.
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AT™ Attachment (ATA)
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The ATA Interface is the predominantly used storage interface for PC's. ATA was originally defined as a standard for embedded fixed disk storage on IBM AT™ compatible PC's. AT stands for "Advanced Technology", which refers primarily to it's then "revolutionary" 16-bit bus. In recent years ATA-3 and ATA-4 have enhanced the functionality of the ATA interface to increase performance and support a wider range of personal computer storage devices.
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ATA Standards
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Define the physical, electrical, transport, and command protocols for the internal attachment of storage devices on PC's.
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ATA/ATAPI-4
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"AT Attachment with Packet Interface" is a combination of the ATA-4 and ATAPI protocols. It complies with the ANSI X3T13/D96153 - also known as Ultra ATA or Ultra DMA. This is the version of the AT-type interfaces that supports up to 33MB/sec data transfers in burst mode.
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ATA/ATAPI-5
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"AT Attachment with Packet Interface 5" is the latest of the ATA series protocol proposal. This version will support up to 66MB/sec data transfers in burst mode. A significant aspect of this incarnation is the enhancement of data integrity and reliability through internal protocol data error detection and correction algorithms. Also includes a new UDMA "Ground Bus", a 80-wire cable requirement.
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ATA-1
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A device which complies with the ANSI X3.221-1994 "AT Attachment" Interface for Disk-Drives - commonly known as IDE.
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ATA-2
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A device which complies with the ANSI X3.279-1995 "AT Attachment" Interface for Disk-Drives - also known as Fast ATA or Enhanced IDE (EIDE).
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