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IT Glossary

Glossary of Information Technology Terms


Click on a Letter:  A  B  C  D  E  F  G  H  I  K  L  M  N  O  P  Q  R  S  T  U  V  W

A

AT Attachment Packet Interface (ATAPI) A type of hardware interface widely used to connect hard disks, CD-ROMs and tape drives to a PC.  Based on the IDE (Integrated Drive Electronics) interface, ATAPI defines the IDE standard for CD-ROMs and tape drives.  ATAPI is one of the least expensive ways to connect internal peripherals to a computer.

average access time The average time required to begin reading data from a storage device.

average swap time The average time required to change and load a tape.

B

backup A snapshot or copy of data capable of being restored as necessary, usually on removable storage media. 

backup application A software program that is used to perform a backup, restore, or compare operation.

backwards compatibility The ability of a current product to work with computer products from an earlier time period or generation of technology such as disk or tape drives.  Compatibility may be specified as read-write or read only.

backup device Typically, a tape drive used to store data or other information contained on a hard drive for the purpose of offline storage and recovery in case of drive failure or software problems that my cause data or programs to be lost or damaged.

BIOS (basic input/output system) A collection of information (firmware) that controls communication between the central processing unit (CPU) and its input and output peripherals.

bit density Expressed as bits-per-inch (BPI), bit density defines how many bits can be written onto one inch of a disc or tape track.

byte A sequence of binary digits or bits considered as a unit - 8 bits in length.  One byte is sufficient to define all the alphanumeric characters of an alphabet.  Storage capacity of a tape drive is commonly measured in gigabytes, which is the total number of bytes that can be written on a single data cartridge assuming a 2:1 compression ratio.

C

capacity The total amount of data, measured in gigabytes, that can be stored on a single data cartridge.  The capacity of data cartridges always assumes that data can be written at a 2:1 compression ratio.  Compressed Capacity: Effective capacity after data has been processed to reduce storage space required while maintaining data integrity - software and hardware compression are available.  Uncompressed Capacity for data that has not been processed to reduce the effective size or volume; sometimes referred to as "native".

CD-RW (ReWritable) A compact disc that can be written, erased, and rewritten using optical methods.  client/server Architecture where computing responsibility is distributed between front-end and back-end systems and programs.

compressed capacity A measurement, usually in Gigabytes, used to define the amount of space available to electronically store data after it has been processed to minimize its effective size while maintaining data integrity.

compression (data compression) Digital data can be compressed by encoding repeatable patterns of binary 0's and 1's.  Compression depends entirely on the type of file and compression algorithm used, and can be the result of a software algorithm or hardware circuitry.  The more patterns that can be found, the more that data can be compressed.  Text can generally be compressed to about 40% of its original size, and graphics files from 20% to 90%. 

D

DAT (Digital Audio Tape) A magnetic tape technology for backing up data using helical scan recording.  DAT uses 4mm cartridges that look like small audiocassettes and conform to the DDS (Digital Data Storage) standard.  The DDS standard specifies the format and quality level of DAT technology for computer storage.  With capacity points from 4-240GB, DAT or DDS is the industry standard in the workstation, PC and midrange server environments. 

data transfer rate The speed at which a tape drive can write digital data to a data cartridge.  Transfer rates are usually measured in megabytes per minute and represent the highest sustainable speed at which the drive is able to operate. 

data integrity Ensuring that the data recorded on a tape cartridge can be restored to a disc drive in its original state.  By using Error Correction Codes (ECC) and other techniques, Seagate tape drives automatically detect incorrectly recorded data and correct it to ensure accurate data restores.  DDS (Digital Data Storage) A data-storage format that was developed from digital audio tape (DAT) to reliably store computer data.  DDS is defined by international standards and is supported by many manufacturers, but more importantly, it is subject to thorough collaborative testing programs, which ensure that tapes (or media) written by one manufacturer's drives can be read by those of other manufacturers.

differential SCSI The Differential SCSI interface allows longer cable lengths from the drive to the host with no degradation of signal.  It is ideal for large server applications. 

digital Describes any system or subsystem that processes binary signals (values of 1 or 0 only).  An example of a non-digital signal is an analog signal that continuously varies, such as RF or audio.  DVD-RAM A high-density optical disc that can be written, erased, and rewritten by the user. 

DVD-RAM A high-density optical disc that can be written, erased, and rewritten by the user.

Dynamic Powerdown A Seagate technology that stores a small amount of power on the electronics of the tape drive and uses it to smoothly slow both tape reels down simultaneously when a power fault is detected. 

E

ECC (error-correction code) The incorporation of extra parity bits in stored data in order to detect errors that can be corrected by the drive when the data is read.  ECC circuits correct data errors at the bit level. 

ElectroStatic Discharge (ESD) Small static discharges that can destroy the circuitry of integrated circuits (chips).  Personnel handling electronic equipment should ground themselves before touching the equipment.  Electronic equipment should always be handled by the chassis or frame only. 

Enhanced IDE (
Integrated Drive Electronics) A high-speed, low cost interface to connect up to 4 devices found on 99% of PCs.  Excellent interface for hard discs, tape drives and CD-ROMs.  Ethernet An access protocol that runs over coaxial or twisted pair wires with a typical data-transfer rate of 10 and 100 million bits per second.

E-PROM (erasable - programmable read only memory) A form of Read-Only Memory used to store the basic software (BIOS) used to start up a computer system or load the operating system software and facilitated the communications between the CPU and input / output peripherals.  This form of memory has two rows of pins, and is installed in a socket.  It must be removed from the socket and placed in a special eraser / writer machine to be programmed.  Common sizes of E-PROMS are 16K, 32K, 64K, 128K and 256K bytes.

F

firmware A computer program (software) containing device-specific characteristics, that is stored in semi-permanent memory (thus the term "firm") that is preserved when the system is powered off.  This type of memory is known as an E-PROM or FLASH memory.  If the firmware code is stored in Flash Memory, then it can be updated or re-written without removing the memory chip(s).  Then it is said to be "flashable" firmware.

full-height drive A 5.25" disk or tape drive that is designed to fit in a 3.25" high enclosure.  This is the size of the original 5 and 10 megabyte MFM disk drives used in personal computers in the early 1980's.


G

gigabyte (Gbyte or GB) 1,000 megabytes or 1,000,000,000 bytes.   More accurately defined as 2 to the power of 9, or 1024 x 1024 x 1024 = 1,073,741,824.  Computer storage manufactures use one billion bytes value which makes the size of their devices sound better.

H

half-height drive A drive that is 1.63 inches high.  This is half of the height of older Full-Height 5.25" drives.

hard disc drive A device that stores data on and retrieves data from non-flexible (hard) rotating discs.

hardware data compression Data compression can be performed either within the electronics of the tape drive (hardware data compression) or by the backup software application (software data compression).  Having the tape drive perform the data compression operation frees the CPU from this task and improves the efficiency of the overall computer system.

head An electromagnetic device that can write/record, read/playback or erase data on magnetic media.  Examples include: monolithic, composite, thin-film and magneto-resistive. 

helical scan A tape mechanism in which the read/write heads are mounted on a tilted, spinning drum that records the data diagonally across the tape surface.  The tape is drawn halfway or further around the circumference of the drum, which reads or writes diagonally to the tape.  This design, similar to a VCR or Camcorder, is used in some computer tape drives such as the common 8mm format.

hubs Small reels used to hold the tape in tape backup devices.  Also a name for a concentrator device used to connect multiple computer systems to a local area network (LAN). 

HVD (High Voltage Differential) A derivation of Ultra SCSI that allows for the use of data cable lengths up to 25 meters. 

I

interface The tape drive interface is the "language" or protocol a drive uses to communicate with a host computer or network.  The main types of tape-drive interfaces used today include ATAPI (IDE), SCSI, and USB. 

K

kilobyte (Kbyte or KB) Nominally refers to 1,000 bytes, especially when it is used to describe drive capacity.  When used to describe semiconductor memory, however, it represents 1,024 bytes (2 to the 10th power)

L

linear A traditional tape mechanism similar to that of an audio cassette player in which the tape is drawn past stationary heads. 

linear density The number of bits per inch (bpi) stored on a tape.

local area network (LAN) A series of computers connected into a system to allow communication and sharing of peripherals.  Usually consists of a file server and one or more workstations.

low voltage differential (LVD) See Ultra 2 SCSI. 

Linear Tape Open (LTO) Technology An open-format tape technology addressing the capacity, performance and reliability requirements of the high end of the tape market.  This technology was created through the joint efforts of HP, IBM and Seagate.  Seagate's Viper 200 is based on the Ultrium format of Linear Tape-Open technology and offers a first generation capacity of 200Gbytes per cartridge.  Seagate offers LTO Ultrium format drives and autoloaders under the Seagate Viper family of products.  See Also: “Ultrium format”. 

LTO CM A 64-Kbit memory chip built into the LTO tape cartridge for faster, more reliable access to data.  Unlike conventional tape cartridges that must be rewound to the beginning of the tape to read the system log or find a desired file, LTO drives can use the memory in the cartridge to access that information immediately. 

M

Magneto-Optical (M-O) A re-writable optical disc that uses a combination of magnetic and optical methods.  MO disks use removable cartridges and come in two form factors -3.5" discs (up to 640-Mbyte) and 5.25" discs (up to 2.6-Mbyte per side).  The 5.25" discs are double sided, but must be removed and flipped over. 

Mean Time Between Failure (MTBF) The average time that a component is expected to work without failure.  MTBF is the result of dividing the number of hours that a component is observed by the number of failures occurring during that period of time. 

Mean Time To Repair (MTTR) The average time to repair a given unit.  Limited to a qualified technician with proper equipment. 

media The magnetic layers of a disc or tape. 

megabyte (Mbyte or MB) Nominally refers to 1,000,000 bytes, especially when it is used to describe drive capacity.  When used to describe semiconductor memory, however, it represents 1,048,576 bytes (2 to the 13th power)

model number The drive Model number is a manufacturers unique identifying code for each type of component.  The model numbers are often grouped by a devices form factor, capacity and/ or interface type. 

modulated frequency method (MFM) A storage technology used in early personal computer disk drivers with a storage capacity ranging from 5MB to nearly 200MB.

MR heads Magnetoresistive heads - a technology in recording heads, which allows higher bit densities.  This head consists of two elements: one for reading and another for writing. 

MSBF (Mean Swaps Between Failure) A statistical calculation or number that loosely denotes the reliability of the robotics associated with tape autoloaders and libraries.  The higher the MSBF, the more swap cycles (cartridge exchanges) the mechanism can be expected to perform without failure.

multitasking The ability of a computer system to execute more than one program or program task at a time. 

multiuser The ability of a computer system to execute programs for more than one user at a time. 

N

native capacity A measurement, usually in Gbytes, used to define the amount of space available to electronically store data without alteration, e.g. hardware or software compression

near-line storage Data not immediately accessible by the host but available without human intervention (for example, a data-storage library system).

node Any computer on a network.

non-volatile memory Memory that will not be erased if power is lost.  Typically, the BIOS of a computer is written in non-volatile or permanent memory.  Flash and E-PROM are two common forms of non-volatile memory.

O

off-line Processing or peripheral operations performed while not connected to the system CPU through the system BUS.

ongoing reliability testing (ORT) Intended to establish the reliability of a product by an extended functional test under realistic user conditions.

open tape format specification A specification that allows for compatible and interchangeable, but technologically independent tape products to be marketed.  Typically, the technology owners will license the technology to various manufacturing partners.  The benefits of an open format are multiple, interchangeable sources of supply, strong competition between format products, lower pricing and faster technology innovation.  Examples are Travan, DDS and LTO technology. 

operating system An operating system is a program that acts as an interface between the user of a computer and the computer hardware.  The purpose of the operating system is to provide an environment in which a user can run programs. 

P

parallel A type of recording in which a byte or group of bytes are recorded simultaneously in a vertical line crossing all the tracks on the tape. 

peripheral equipment Auxiliary memory, displays, printers, disc drives, tape drives and other equipment usually attached to the computer system CPU by controllers and cables (they are often packaged together in a desktop computer). 

printed circuit board (PCB) The circuit board with integrated circuits (chips) attached. 

printed wire assembly (PWA) A completed circuit board with components installed.  (Same as PCB)

printed wire board (PWB) A circuit board without components installed, also known as a bare board. 

Partial-response, maximum likelihood (PRML) - advanced technology read channel that contributes to a faster data throughput rate. 

programs (also software programs, or computer programs) are instructions for a computer.  A computer requires software programs to function. Moreover, a computer program does not run unless its instructions are executed by a central processor or CPU; however, a program may communicate an algorithm to people without running. Computer programs are usually executable programs or the source code from which executable programs are derived (e.g., compiled).  Computer programs may be categorized along functional lines: system software and application software. And many computer programs may run simultaneously on a single computer, a process known as multitasking.

protocol A set of rules governing the format of messages exchanged within a communications system.

Q

QIC (Quarter-Inch Cartridge) Defines a standards committee and a variety of tape formats.

R

random access memory (RAM)Memory where any location can read from or write to in random order.  RAM usually refers to volatile memory where the contents are lost when power is removed.  The user-addressable memory of a computer is random access memory. 

read only memory (ROM) A chip that can be programmed once with bits of information.  This chip retains the information even if the power is turned off.  When the information is programmed into the ROM, it is called burning the ROM. 

restore Retrieval of information from a tape drive and the recording of it on a disc drive. 

read while writing (RWW) A method whereby data being recorded onto tape is read and verified on the same pass as it is written.  The ability of a tape drive to write data to tape and immediately read it from the tape and compare it to the original data in the drive's buffer during the same pass of the tape. 

recording speed The maximum sustained data transfer rate that a tape drive can provide, assuming that the data on the tape is stored in compressed form at a 2:1 compression ratio.

A rootkit is a program (or combination of several programs) designed to take fundamental control (in Unix terms "root" access, in Windows "Administrator" access) of a computer system, without authorization by the system's owners and legitimate managers. Access to the hardware (i.e., the reset switch) is rarely required as a rootkit is intended to seize control of the operating system running on the hardware. Typically, rootkits act to obscure their presence on the system through subversion or evasion of standard operating system security mechanisms. Often, they are Trojans as well, thus fooling users into believing they are safe to run on their systems. Techniques used to accomplish this can include concealing running processes from monitoring programs, or hiding files or system data from the operating system.

Rootkits may have originated as regular applications, intended to take control of a failing or unresponsive system, but in recent years have been largely malware to help intruders gain access to systems while avoiding detection. Rootkits exist for a variety of operating systems, such as Microsoft Windows, Linux and Unix. Rootkits often modify parts of the operating system or install themselves as drivers or kernel modules, depending on the internal details of an operating system's mechanisms.

S

SCSI (Small Computer Systems Interface) A high-speed interface standard used to connect up to 15 devices on the same controller.  SCSI is most often used for File Server computers because it is much more expandable that the IDE or ATA interface used in most personal computers.  Common SCSI peripherals include hard discs, tape drives and CD-ROMs.  Prior to the introduction of the USB interface, many flatbed scanners used a SCSI interface.

serial recording A type of data storage in which each byte is recorded one bit at a time on a single track. 

serpentine encoding An efficient recording format that records one track with the tape running in one direction, the next lowest track with the tape running the opposite direction, and so on. 

server A computer deliberately devoted to sharing its files and resources, such as discs and printers, with other computers on the local area network or LAN. 

T

TCP/IP (transmission control protocol/internet protocol) A set of protocols used on the Internet to connect dissimilar computers and offer services such as Telnet and FTP.

Travan Tape technology, based on linear recording, with capacity points from 8-40 Gbytes, represents an efficient cartridge and drive design that reduces tape stress, ensures data integrity and increases drive and cartridge reliability.  Travan mechanisms are known to be very reliable at a cost-effective price point and are the perfect choice for PCs, workstations and entry-level server environments.  Seagate offers bare Travan drives called Hornet Travan and bundled solutions called TapeStor Travan. 

Travan /
Travan NS A backup tape technology that evolved from Quarter Inch Cartridge (QIC).  Travan uses wider tape, different tape guides, and improved magnetic media to yield higher capacities.  Travan Network Series (NS) is a migration from desktop to workgroup server backup and provides hardware compression and read-while-write features.  Depending on the model, Travan drives may be compatible with QIC, QIC-Wide and QIC-EX cartridges. 

U

Ultra ATA Industry-accepted standard that allows a maximum data transfer rate of 33 Mbytes per second using an ATA (IDE) interface. 

Ultra SCSI Ultra SCSI is an evolution of the standard SCSI interface.  Sometimes referred to as Fast 20, Ultra SCSI enables external transfer rates of up to 20 Mbytes per second on an 8-bit bus and up to 40 Mbytes per second on a 16-bit bus.  Ultra SCSI uses the same physical connections as SCSI-2 and is fully backward compatible.  To reach the maximum transfer rates of up to 20 (8-bit) or up to 40 (16-bit) Mbytes per second, the controller and disc drive both must be Ultra SCSI devices.  Ultra SCSI also reduces total cable lengths to half of the Fast SCSI-2 specification.  Ultra SCSI represents the parallel SCSI solution defined in the SCSI-3 ANSI standard specification. 

Ultra2 SCSI Provides bus data rates of 80 Mbytes per second and easy integration of up to 16 devices on the SCSI bus using cable lengths of 12 meters.  Low Voltage Differential doubles SCSI bus rates and provides the integration flexibility and data integrity of High Voltage Differential at single-ended costs.  Ultra2 SCSI LVD is fully backward compatible to all previous single-ended versions of SCSI, taking advantage of the previously installed multibillion-dollar product base.  When an Ultra2 drive is installed on a previous version SCSI bus, performance will de-fault to the specifications of that bus. 

Ultrium format The high capacity format used in Linear Tape-Open technology.  The Ultrium format specifies those technologies required for consistent and reliable data interchange between drives manufactured to the Ultrium specification.  The Ultrium format provides for up to 200 Gbytes of compressed (2:1) data storage per cartridge on half-inch tape.  Also specified is a compressed (2:1) transfer rate of up to 40 Mbytes per second.  Also see Linear Tape-Open technology.  Using a single-reel tape cartridge to maximize capacity, the Ultrium tape format is ideally suited for backup, restore and archive applications.  Seagate provides Ultrium format tape drives through its Viper family.

Uncompressed Native e.g. data that has not been processed to reduce the effective size or volume; or unaltered, e.g. compressed data that has been processed to restore redundant strings of data previously removed through the use of a compression algorithm.

unformatted Drive byte capacity before formatting.  Maximum capacity of a disc drive before formatting, which is equal to bits per track times the number of heads times the number of cylinders. 

USB (Universal Serial Bus) Universal Serial Bus (USB) is the simple way to connect peripherals to your computer.   It can be used to attach a wide variety of devices like scanners, cameras, keyboards, and speakers - almost anything to your computer.   USB for great for attaching medium speed devices to computers.  It's maximum speed of 12 Mbps is fine for low speed devices like keyboards, mice, or joysticks.  It is also well suited for medium speed devices like tape drives, hard disc drives, cameras, modems, or scanners.  Also, because it's "hot-pluggable" you can plug devices in or unplug them safely when you computer is turned on.  Using either multiple ports on your computer or a hub, you can attach an almost unlimited number of devices - theoretically up to 127 if you have them. 

V

verification This feature lets the backup software application compare the data written to the original information to the data was written correctly. 

volatile memory Memory that will be erased if power is lost.  Typically, the main memory (RAM memory) of a computer system is volatile. 

W

wide area network (WAN) A communications system used to connect computers and other devices across a large area.  It can be a private connection or a public (phone) network. 

write To access a storage location and store data on some form of magnetic media by encoding the magnetic particles in the media using a Read/Write head.

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