Retrieval of data from or transfer of data to 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 a drive that contains the operating system. If a drive has multiple partitions, only the primary partition can be made active. A drive can have only one active partition.
Active Power Save™
Drive feature that delivers seek mode power consumption through an advanced WD firmware which conserves power in active seek modes without degrading performance.
active termination
One or more voltage regulators that produce termination voltage. The voltage regulator(s) drives a constant voltage along the bus to ensure that the data signal remains 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 read/write heads.
adaptive cache
A feature of WD drives that enables improved performance and throughput by adapting to the application being executed.
address
In the hard drive industry, there are several types of addresses: a drive (unit address), radial position (cylinder address), or circumferential position (sector address).
AES
Advanced Encryption Standard. 128-bit encryption technology used in WD Sync software.
AFR
Annualized failure rate. A method of measuring failure rates or trends for a group of units at a site. The rates are based on the monthly total number of returned field failure units divided by the total cumulative installed base and multiplied by 12 (to annualize the failure rate).
allocation
The method DOS uses to assign a specific area of a drive to a particular file. See also cluster.
ANSI
American National Standards Institute. A U.S. governmental body responsible for approving U.S. 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 (bits per inch (BPI)) by the track density (tracks per inch (TPI)).
ASP
Average selling price.
asynchronous transmission
Transmission in which each byte of information is synchronized individually by using request (REQ) and acknowledge (ACK) signals.
ATA
Advanced Technology Attachment. A name used by ANSI to describe what the computer industry calls integrated drive electronics (IDE).
ATA-6
The current version of ATA.
auto defect retirement
The automatic mapping out and relocation of defective sectors found during read or write operations.
auto park
Moving read/write heads to a safe non-data landing zone and locking them into place, caused by turning off power to the drive.
AV
Audio/video.
average access time
The average time a drive requires to perform a seek operation, usually measured by one-third stroke.
average seek time
The average time a drive requires to move read/write heads to a safe non-data landing zone and lock them in place.
bandwidth
The amount of data that can be sent over a circuit. See also buffer bandwidth.
binary
Having two components or alternatives. Binary numbers are expressed as combinations of two digits, 0 and 1.
BIOS
Basic input/output system. A program, or set of programs, that controls basic computer functions.
bit
An abbreviation of binary digit, which can be either 0 or 1. A bit is the basic data unit of all digital computers and capacity of computer storage devices. 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. Eight bits equal one byte.
bit density
The number of bits that can be written onto one inch of track on a disk surface, expressed as bits per inch (BPI).
block
A group of bytes handled, stored, and accessed as a logical data unit, for example, an individual file record. A block in UNIX workstation environments is the smallest contiguous area that can be allocated for data storage. Note: A different definition of this term applies when referring to the physical configuration of a hard drive.
boot
To start or restart a computer; which loads the operating system.
BPI
Bits per inch. A measurement of the density of information on a hard drive. See also bit density.
buffer
A temporary data storage area to allow for a different rates of data transfer and/or processing between sender and receiver. For example, a printer buffer accepts data from a computer and holds it until ready to print.
buffer bandwidth
The speed of transferring data to or from a buffer.
build-to-order
The assembly of a computer system in response to a customer order, rather than for inventory or mass shipment. A system used by Dell and Gateway, now being emulated to some degree by other PC manufacturers such as IBM, HP, and Compaq.
burst mode transfer rate
The transfer rate into buffer RAM on a hard disk. This rate does not include delays due to latencies or hosts. See also transfer rate.
bus
A path that carries data between a computer (microprocessor) and peripheral devices. An IDE interface cable or a SCSI cable is an example of a bus.
business model
A company financial plan, including product pricing and margin calculations.
byte
A sequence of eight binary digits or bits regarded as a unit or binary word. The storage capacity of a hard drive is commonly measured in megabytes, which is the total number of storable bits divided by eight million.
cache
High-speed RAM used as a buffer between the CPU and a hard drive. A cache retains recently accessed information to accelerate subsequent accesses to the same data. When data is read from or written to disk, a copy is saved in the cache, along with its associated disk address. The cache monitors addresses of subsequent read operations and, if requested data is already in the cache, immediately returns the data. If requested data is not in the cache, it is fetched from disk and saved in the cache.
capacity
Also known as storage capacity. The amount of information, measured in bytes, that can be stored on a hard drive. WD defines a megabyte (MB) as 1,000,000 bytes and a gigabyte (GB) as 1,000,000,000 bytes. Some operating systems use the binary numbering system which results in a lower reported capacity.
CCC
Customer configuration code. 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.
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
The final assembly of a system by a distributor or reseller, from kits provided by a manufacturer and components shipped directly to the assembler by subsystem makers.
CHS addressing
Cylinder, head, sector addressing. A method of referencing drive sectors as a collection of unique cylinder, head, and sector addresses. Each block on a drive has a unique CHS address.
CIFS
Common Internet File System.
clamshell
A hinged, bifolded encasement. Packaging in which product is sold.
clean room
An environmentally controlled, dust-free assembly or repair facility in which hard drives are assembled or opened for internal servicing.
cluster
An allocation unit. At least one cluster is allocated to each file stored in a DOS environment. Cluster size increases with 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, regardless of file size. To avoid wasting space on small files, create multiple, smaller partitions.
CMOS setup
A program supplied in most systems that allows a user to configure internal and external devices.
cold swap
Act of swapping out a hard drive with the system powered off.
command aging
A SCSI feature that prevents a command reordering algorithm from delaying I/O processes in the command queue for extended periods of time.
command queuing
A technology designed to increase performance of SATA hard drives by allowing disk firmware to optimize the order in which read and write commands are executed. This may result in increased performance for workloads where multiple simultaneous read/write requests are outstanding, a situation that typically occurs in server-type applications. Normal desktop applications benefit less from command queuing and, in some cases, performance may be reduced due to added overhead.
command reordering
A feature that allows a drive to reorder I/O processes in the command queue, which results in minimal seek time and rotational latency, and increased throughput.
controller
See disk controller, disk drive controller, and interface controller.
controller card
An adapter with the control electronics for one or more hard drives, usually installed in a bus slot of a computer.
correctable error
An error that the drive can correct by using error detection and correction schemes.
CRC
Cyclic redundancy check. A value stored or transmitted with data to detect corruption. By calculating a CRC and comparing it to the original data sent, a receiver can detect some types of transmission errors.
CSEL
Cable select. An alternative to Master/Slave designation in a dual-drive configuration. Master/Slave designation is based on the position of drives relative to the cable. Special cabling from a system manufacturer is required to ground the CSEL signal selectively on one IDE cable connector. For example, when one drive is connected to the grounded CSEL conductor, it configures itself as Master; the second drive connected to the other connector, on which CSEL is not grounded, becomes the Slave. CSEL eliminates the need for unique jumper configurations between Master and Slave drives.
cylinder
The cylindrical surface formed by identical track numbers on vertically stacked disks.
Data Lifeguard Tools™
A set of software utilities that work in conjunction with embedded Data Lifeguard features to make hard drive installation, drive management diagnostics, and repair simple and worry-free.
Data Lifeguard™
A WD-exclusive data reliability feature that automatically detects, isolates, and repairs problem areas on a hard drive and prevents data loss.
data synchronizer
An electronic circuit that uses a clock signal to synchronize data.
data transfer rate
The rate that digital data transfers from one point to another, expressed in bits per second or bytes per second. Data transfer rate to disk (internal disk transfer rate) is expressed in megabits per second (Mb/s). Data transfer rate from buffer to host (transfer of buffered data) is expressed in megabytes per second (MB/s).
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.
dedicated landing zone
The designated radial zone of a disk, usually at the inner portion, where heads are stored to avoid contact with data cylinders when power to the drive is off.
defect free
A term to describe recording surfaces that have no detectable defects.
defect management
A general method of eliminating data errors on a recording surface by mapping out known media defects. Defective areas are rendered inaccessible, so that subsequent operations write data only to non-defective locations.
desktop
A personal computer sized to fit on or under your desktop. WD EIDE hard drives are designed to fit into desktop PCs.
DHCP
Dynamic host configuration protocol. A protocol for assigning IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address each time it connects to the network. In some systems, the device's IP address even changes while it is still connected. DHCP also supports a mix of static and dynamic IP addresses.
differential SCSI
An electrical signal configuration that uses pairs of lines for data transfer, primarily in applications requiring cable lengths up to 82 feet (25 meters).
disk
A rigid platter, stored inside a hard drive, usually constructed of aluminum or Mylar® and with a magnetic surface that allows the recording of data.
disk controller
A chip or circuit that controls data transfers between disk and buffer. See also disk drive controller and interface controller.
disk drive controller
Hard disk drive controller electronics, which include the disk controller and interface controller. See also disk controller and interface controller.
disk transfer rate
Speed at which data is transferred to/from disk (platter); a function of the recording frequency. Typical units are bits per second (b/s), or bytes per second (B/s). A hard drive disk transfer rate increases from the inner diameter to the outer diameter of the disk.
distribution channel
Electronics distributors and retail chains that deliver electronic goods to end users through value-added resellers and retail stores.
DMA
Direct memory access. A process that transfers data directly to/from main memory, without passing through a CPU. DMA improves speed and efficiency by allowing a system to continue CPU processing while transferring data to/from a hard drive.
DOS
Disk operating system. A computer program that controls the organization of data, files, and processes on a computer.
dual interface
An external storage device with two interfaces available for connection to the computer.
dual-option backup
The ability to back up a drive either manually (on demand) or automatically.
DuraStep Ramp™
WD technology that locks the heads of a data disk to provide additional shock protection.
duty cycle
The time a component, device, or system is actually operating as compared to the time it is powered on; can be expressed as a ratio or percentage.
DVR
Digital video recorder.
EasyLink™
A WD utility that allows users to locate and set up a drive as a local drive from any computer quickly and easily.
ECC
Error correction code. A mathematical algorithm that detects and corrects data errors.
ECC on the fly
A hardware correction technique that corrects errors in the read buffer before host transfer and without any performance penalties. These error corrections are invisible to the host system because they do not require assistance from drive firmware.
EESA
Enterprise extensions S.M.A.R.T. accessed. An expanded command set that provides SCSI-like control for server environments, optimizing operation and performance when drives are used in vibration-prone multidrive systems such as rack-mounted servers.
EIDE
Enhanced integrated drive electronics. The primary interface used by desktop PCs to handle communication between hard drives and the central processing unit (CPU). The equivalent interface in most enterprise systems is SCSI.
embedded servo control
A design that generates accurate feedback to the head position servo system without requiring a full data surface, because servo control data is stored on every surface (unlike dedicated servo control).
encoding
A process of modifying data patterns before writing them onto a disk surface.
enterprise
A series of computers employed largely in high-volume and multi-user environments such as servers or networking applications. Enterprise systems may include single-user workstations required for design, engineering, and audio/video applications.
enterprise storage group
The WD operation that designs, produces, and markets hard drives for the enterprise market.
error log
A record that contains error information.
error rate
The quantity of errors of a particular type that occur when reading a specified number of bits.
Ethernet
A standard method of connecting computers to a Local Area Network (LAN) using coaxial cable.
extended partition
A partition on a disk where non-system files (other than DOS or operating system files) can be stored. Multiple partitions can be created on a hard disk: one primary partition and one or more extended partition(s). Operating system files must reside on the primary partition; logical drives can be created on an extended partition.
FAT
File allocation table. A data table stored at the beginning of each partition on a disk and used by the operating system to determine which sectors are allocated to each file and in which sequence.
FAT32
A file allocation table system with a maximum file transfer of 4 GB and a maximum partition size of 32 GB.
FC
Fibre channel. 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.
FC-AL
Fibre channel-arbitrated loop. A serial storage interface designed for high-end applications. A subset of FC network systems interconnection.
FDB
Fluid dynamic bearings. A design that incorporates a layer of lubricant instead of ball bearings in a hard drive spindle motor, thus providing increased storage capacity, non-operational shock resistance, speed control, robust shipping and handling, and improved acoustics.
FDISK
A software utility that partitions a hard drive. This utility is included with DOS and Windows® 95 operating systems.
Femto slider
Form factor in which the read/write head is mounted on the small, lightweight femto slider which allows the head to move more quickly from track to track on the disk.
fetch
The process of retrieving data.
FireWire 400
FireWire400 supports data transfer rates up to 400 Mb/s.
FireWire 800
FireWire 800 has a maximum data transfer rate of 800Mb/s. It is backward-compatible with FireWire 400 using an optional adapter.
FireWire®
This high-speed serial bus, also known as IEEE 1394, provides a non-proprietary, high-performance method of interconnecting digital devices.
firmware
Permanent instructions and data programmed directly into the circuitry of read-only memory for controlling computer operations.
fiscal periods
Three-month segments of a fiscal year. WD's fiscal year has fiscal quarters ending on the last days of September, December, March, and June.
FIT
Functional integrity testing. A suite of tests WD performs on all its drive products to ensure compatibility with different hosts, operating systems, adapters, application programs, and peripherals. This testing is performed before a product is released to manufacturing.
FlexPower™
Connector technology that accepts power from both industry-standard and new SATA power supplies.
flow control
In programmed input/output transfers, the ability of an EIDE drive to control the speed at which a host transfers data to/from a drive by using an IORDY signal. A host temporarily stops transferring data when a drive deasserts the IORDY signal; the host continues transferring data when the drive reasserts the IORDY signal.
form factor
An industry standard term for the physical and external dimensions of a device.
format
A process that prepares a hard drive to store data. Low-level formatting sets up the locations of sectors so that user data can be stored in them. High-level formatting erases all information on a hard drive and sets up the system required for storing and retrieving files. WD hard drives are low-level formatted at the factory and therefore need not be low-level formatted by end users. A high-level format (with EZ-Drive or the Format command) must be performed on your new WD hard drive before use.
formatted capacity
The actual capacity available to store data in a mass storage device. The formatted capacity is the gross capacity minus the capacity used by overhead (formatting).
full-duplex
A communication protocol that permits simultaneous transmission in both directions.
GB
Gigabyte. WD defines a gigabyte as 1,000,000,000 (one billion) bytes or 1000 (one thousand) megabytes.
GMR
Giant magnetoresistive. An advanced form of head technology.
GPS
Global positioning system. Provides specially coded satellite signals which can be processed in a GPS receiver to compute position, speed, and time.
HAD
Head disk assembly. The mechanical components of a hard drive, including disks, heads, spindle motor, and actuator.
half-duplex
A communication protocol that permits transmission in both directions but in only one direction at a time.
half-height drive
A drive measuring 1.6 inches in height. Standard 3.5-inch hard drives are available in heights of 1.0 inch and 1.6 inches.
hard drive
An electromechanical device for information storage and retrieval, incorporating one or more rotating disks on which data is magnetically recorded, stored, and read. The principal products of WD.
hard drive industry
The combined manufacturers of hard drives. In the United States, the industry is led by Seagate, WD, and Maxtor.
hard error
An error that is repeated 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
Also known as a read/write head. An electromagnetic coil and metal pole that read/write magnetic patterns on a disk. A drive with several disk surfaces or platters has 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
The damage incurred to a read/write head when the head comes into contact with a disk surface. A head crash may be caused by severe shock, dust, fingerprints, or smoke, and may damage the disk surface and/or head.
head loading zone
The area on a disk reserved for heads to take off or land when power to the drive is turned on or off. No data is stored in the head loading zone.
head stack assembly
An electromechanical component containing read/write heads and their supporting devices.
headerless format
The lack of headers or ID fields (track format). This format enables greater efficiency and increased user capacity.
HFS
Hierarchical File System. File system developed by Apple Computer for use on computers running Mac OS.
high-level formatting
Formatting that erases all information on a hard drive and sets up the system for storing and retrieving files. This must be performed (with EZ-Drive or the Format command) on your new WD drive before use.
host
The computer to which other computers and peripherals connect. See also initiator.
host adapter
A plug-in board that acts as an interface between a computer system bus and a hard drive.
host interface
The point at which a host and a drive are connected to each other.
host transfer rate
The speed at which a host computer can transfer data across an interface.
hot plug
Act of swapping out a hard drive without having to power down the system or reboot. Hot plugging capability promotes system design flexibility, data availability, and serviceability.
hot swap
See hot plug.
hub
In a network, a device joining communication lines at a central location, providing a common connection to all devices on the network.
I/O
Input/output. An operation or device that allows input and output.
IDE
Integrated drive electronics. A technology in which interface controller electronics are incorporated into the design of the hard drive rather than into 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 the index.
initialization
See low-level formatting.
initiator
A device in control of a SCSI bus that sends commands to a target. Most SCSI devices have a fixed role as either initiator or target; however, some devices can assume both roles.
input
Incoming data that a computer processes, such as user-issued commands.
IntelliSeek™
WD AV feature that optimizes seek speeds to lower power consumption, noise, and vibration.
interface
A hardware or software protocol to manage the exchange of data between a device and a computer; the most common ones are PATA (also known as EIDE), SATA, and SCSI.
interface controller
A chip or circuit that translates computer data and commands into a form usable by a hard drive and that controls data transfers between buffer and host. See also disk controller and disk drive controller.
interleave
The arrangement of sectors on a track.
interrupt
A signal sent by a subsystem to the CPU when a process either was completed or could not be completed.
IP
Internet Protocol. A system that controls how data messages are separated into packets, routed from the sender, and reassembled at the destination.
IP address
A 32-bit, binary number that uniquely identifies a computer connected to the Internet.
ISA
Industry Standard Architecture. The standard 16-bit AT bus for the PC/AT system. ISA was the only industry standard bus for PCs until the recent release of microchannel architecture (MCA), Extended Industry Standard Architecture (EISA), and Peripheral Component Interconnect (PCI).
JIT
Just-in-time. A production and inventory control process in which components and materials are delivered to an assembly point as needed. This process is used in WD manufacturing facilities and in most of its customer plants.
jumper
An electrically-conductive component in EIDE drives that is placed over pairs of pins extending from the circuit board on the hard drive jumper block to connect them electronically. For example, a jumper is one method of designating a hard drive as Master or Slave. The jumper block is located next to the 40-pin connector on a hard drive.
KB
Kilobyte. Usually, this is a unit of 1000 bytes. In computer memory, which is partitioned into sizes that are a power of 2, a kilobyte is equal to 210 or 1024 bytes.
LAN
Local area network. A system in which computer users in a company or an organization are linked to each other and often to collections of data centrally stored in LAN servers.
LAN
Local Area Network. 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.
landing zone
A location on the inner part of a disk to which heads move when commanded or when powered off. User data is not stored in the landing zone.
laser texture
A treatment that minimizes friction and wear on a hard drive. The precision and consistency of this process contributes to the robustness of WD drives.
latency
The period of time that read/write heads wait for a disk to rotate to the correct position for accessing requested data. For a disk rotating at 5200 RPM, average latency is 5.8 milliseconds (one-half the revolution period).
LBA
Logical block addressing. A method of addressing sectors on a drive as a single group of logical block numbers rather than cylinder, head, and sector addressing (CHS). LBA allows accessing larger drives than is normally possible with CHS addressing.
LED
Light-emitting Diode. An electronic device that lights up when electricity is passed through it.
logical address
A storage address, which may not describe the physical location, for requesting data retrieval. A controller converts a request from a logical to a physical address and is able to retrieve data.
logical drive
A section of a hard disk that appears to be a separate drive in a directory structure. Up to 23 logical drives can be created on an extended partition of a hard disk, using letters A-Z with three reserved: A and B for diskette drives, and C for the first primary DOS partition. Logical drives are commonly used for group directories and files.
logistics model
A system by which a company organizes the physical distribution of its products. A hard drive manufacturing model may include portions to OEM customers, distributors, retail chains, or all of these.
low-level formatting
A process, also called initialization, that prepares a hard drive to store data. Low-level formatting sets up the locations of sectors so that user data can be stored in them. Low-level formatting is performed at the WD factory; users need not perform low-level formatting on a WD drive.
LP
Low profile. The process of creating sectors on a disk surface, which permits the operating system to create the file structure. Also called initialization. Low-level formatting is performed at the WD factory; users need not low-level format a WD drive.
LUL
See Ramp Load/Unload
magnetic flux
A pattern of magnetic pole directions of bits written on a disk.
manufacturing yield
The part of unit production of a manufacturing process that is usable, saleable product; usually expressed as a percent of a product's total output.
Master
The primary drive in a dual-drive configuration. A Master drive by itself (with no Slave) is called a single drive.
MB
Megabyte. WD defines a megabyte as 1,000,000 (one million) bytes.
mechanical latency
A time period, including both seek time and rotational latency. Mechanical latencies are the main hindrance to higher performance in hard drives and are one hundred times greater than electronic (non-mechanical) latencies associated with data transfers. See also rotational latency and seek time.
media
In hard drives, the disks and their magnetic coatings. Sometimes refers only to the coating material.
Media Center
WD's storage product that combines an external hard drive, 8-in-1 memory card reader, dual-option backup, and USB 2.0 hub.
memory
A device or system capable of storing and retrieving data.
MFM
Multiple frequency modulation. A method of encoding analog signals into magnetic pulses or bits.
mirroring
The process of generating an exact copy of saved data from one drive to another drive within a RAID 1 system. Each drive can be accessed and read separately. A mirrored drive can be removed from a system while the other drive(s) are still active. See also RAID 1.
MP3
MPEG-audio layer 3. A digital audio coding scheme for distributing music over the Internet.
MR head
Magnetoresistive head. MR heads were developed to increase areal density and improve drive performance. These heads use an inductive element for writing data and a separate magnetoresistive element for reading data, rather than traditional inductive thin-film, read/write heads. 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 allows reading higher areal density data.
MTBF
Mean time between failures. The average time (expressed in hours) that a component works without failure. This time 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. Only major subassemblies (the PCB, sealed housing, etc.) are changed in the field; component level repairs are not performed in the field.
multimedia
A simultaneous presentation of data in more than one form, such as by means of both video and audio.
multi-user
A system in information technology that enables more than one user to access data at the same time.
My Book™
Trade name for WD external hard drives with a book-shaped enclosure.
NAS
Network attached storage. Hard disk storage that is set up with its own network address rather than being attached to the computer that is serving network workstation users
NCQ
Native command queuing. A command protocol implemented only on native SATA hard drives. It allows multiple commands to be outstanding within a drive at the same time. Drives that support NCQ have an internal queue where outstanding commands can be rescheduled and re-ordered dynamically, along with necessary tracking mechanisms for outstanding and completed parts of the workload. NCQ also has a mechanism that allows the host to issue additional commands to the drive while the drive is seeking data for another command.
NetCenter™
Trade name for WD's first generation external network hard drive.
network computer
A computer with limited data storage capacity that communicates with a central data storage facility such as a server or RAID system.
NTFS
NT file system. A file system, designed for Windows® NT, that supports long filenames, security access control, recovery, and other features.
OEM
Original equipment manufacturer. In the case of WD, OEM customers are companies such as Compaq, Dell, Gateway, and IBM.
operating system
Software that allows users and programs installed on your system to communicate with computer hardware such as a hard drive.
partition
A logical division on a hard drive that the operating system treats as a separate hard drive. Each partition is assigned a unique drive letter.
passive termination
A termination architecture that matches impedance at the end of the SCSI bus by using a voltage divider network of passive resistors.
PC
Personal computer.
personal storage division
The WD 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. WD's 4.3 GB-per-platter platform, for example, is the basis for five products ranging in capacity from 4.3 to 13.0 GBs.
platter
A metal (or other rigid material) disk mounted inside a fixed-disk drive. Many drives consist of multiple platters mounted on the spindle to provide more data storage surfaces. A platter may use one or both surfaces to store data.
PMR
Perpendicular Magnetic Recording. Hard drive recording method in which the magnetization of each data bit is aligned vertically to the spinning disk. PMR provides the ability to store more data on a given disk than the longitudinal recording method, enabling the manufacture of hard drives with higher capacities.
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.
Preemptive Wear Leveling (PWL)
Mechanical feature in which the drive arm frequently sweeps across the disk to reduce uneven wear on the drive surface common to audio video streaming applications.
pre-fetch
The process of loading instructions into a queue when the processor's external bus is otherwise idle.
primary partition
The partition where operating system files are stored. To start your operating system from a hard disk, it must have a primary partition and the primary partition must be active.
PRML
Partial response maximum likelihood. A read channel that uses sampled data, active equalization, and Viterbi detection to retrieve user data accurately from disk.
product road map
A company plan for the introduction of new products.
programmed I/O
In a hard drive with an AT interface, data transfers between a drive and a host using programmed I/O (PIO). A host uses PIO to write to command block registers (CBRs) when transmitting control information, such as the location of a read command.
protocol
A convention of data transmission that defines timing, control format, and data representation.
proximity recording
A technology that increases recording density by allowing a read/write head to come into close proximity to a disk surface.
PVR
Personal video recorder.
qualification
A process by which sample components are tested for their compatibility and utility as parts of a system. WD OEM customers qualify WD hard drives for use in their computers.
queue
A first-in-first-out (FIFO) data structure to sequence multiple demands for a resource such as a printer, processor, or communication channel. A host appends objects to the end of a queue and removes them from the front.
R&D
Research and development.
radial path
A straight-line path from the center of a disk to the outer edge.
RAFF™
Rotary Acceleration Feed Forward. WD technology that maintains the highest possible data transfer performance in the high rotational vibration environments commonly found in servers and storage arrays.
RAID
Redundant array of independent disks. A grouping of hard drives in a single system to provide greater performance and data integrity.
RAID 0
RAID protocol in which data is striped across multiple hard drives, enabling the accelerated reading and recording of data by combining the work of two or more drives to increase performance. See also striping.
RAID 1
RAID protocol in which two copies of the data are instantaneously recorded - each on separate hard drives. RAID 1 ensures the protection of users' data because in the event that one of the hard drives fails, the other hard drive(s) will continue to read and write data until the faulty hard drive is replaced and rebuilt to once again safely mirror the data. See also mirroring.
RAM
Random access memory. Memory that allows any storage location to be accessed randomly, as opposed to sequential access devices such as tape drives.
Ramp Load/Unload (LUL)
Ramp load parks the recording head off the media when the drive is idle and on spin up, maximizing available disk space and minimizing power usage, which results in lower heat and long-term drive reliability.
RE
RAID edition. A WD drive engineered to thrive in a high-intensity RAID system while still offering traditional desktop value.
read channel
The channel that performs data encoding and conversion that a drive requires to write computer generated information onto a magnetic medium and read back that information with a high degree of accuracy.
read verify
A data accuracy check performed by having a disk read data from a controller, which in turn checks for errors but does not pass data to the system.
read/write head
See head.
recoverable error
A read error that can be corrected by ECC or by re-reading data.
RLL
Run length limited. An encoding scheme used during write operations to facilitate reading that data.
RoHS
Restriction of Hazardous Substances. This compliance Directive 2002/95/EC of the European Parliament, which is effective in the EU beginning July 1, 2006, aims to protect human health and the environment by restricting the use of certain hazardous substances such as lead, mercury, hexavalent chromium, cadmium, polybrominated biphenyl flame retardants, and polybrominated diphenyl ether flame retardants in new equipment.
ROM
Read-only memory. An integrated circuit memory chip containing programs and data that the computer or host can read but cannot modify. A computer can read instructions from ROM but cannot store data in ROM.
rotational latency
The amount of delay in obtaining information from a disk due to disk rotation. For a disk rotating at 5200 RPM, the average rotational latency is 5.8 milliseconds. See also mechanical latency.
RPM
Rotations per minute. Also known as spindle speed. Rotational speed of a medium (disk). Hard drives typically spin at a constant speed. The lower the RPM, the higher the mechanical latency. Disk RPM is a critical component of drive performance, as it directly affects rotational latency.
RPS™
Reduced power spinup. The WD-optimized spinup feature specifically designed for the external hard drive and consumer electronics markets.
S.M.A.R.T.
Self-monitoring, analysis, and reporting technology. A technology to assist users in preventing system down time due to hard drive failure; it attempts to predict hard drive failure before it occurs.
Safe Shutdown™
A WD-exclusive feature that ensures all data is transferred before shutting down the drive.
SATA
Serial advanced technology attachment. A standard for connecting hard drives to computer systems, based on serial signaling technology. Its practical advantages over PATA (also known as EIDE) are longer and thinner cables for more efficient airflow within a form factor, fewer pin conductors for reduced electromagnetic interference, and lower signal voltage to minimize noise margin.
SCA-2
Single connector attached. An interface that incorporates a grounding contact, blindmate connector, direct plug misalignment tolerance, ESD protection, hot swap capability, and backplane connector options for SCSI devices. SCA-2 is commonly called the 80-pin SCSI connector.
SCAM
SCSI configure automatically. Allows users to attach SCSI devices without worrying about configuration options.
SCSI
Small computer system interface. An interface between a computer and peripheral controllers, commonly used in enterprise computing and Macintosh systems. Pronounced scuzzy. The equivalent interface system in most personal computers is enhanced integrated drive electronics (EIDE).
SCSI device
A host computer adapter, peripheral controller, or intelligent peripheral that can be attached to a SCSI bus.
SCSI-1
A SCSI version (ANSI document X3.131-1986).
SCSI-2
A SCSI version (ANSI document X3.131-1994).
SCSI-3
A SCSI version under development (ANSI X3T10 Working Documents).
sector
A 512-byte packet of data in EIDE and SCSI hard drives. This is the smallest amount of data that can be read from or written to a drive from a host interface. On Macintosh and Unix drives, sectors usually are grouped into blocks or logical blocks that function as the smallest data unit permitted. Since these blocks often are defined as a single sector, the terms block and sector are sometimes used
