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.


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


Software that detects, repairs, cleans, or removes virus-infected files from a computer.


Short for Advanced Technology Attachment, a disk drive implementation that integrates the controller on the disk drive itself.


ATA Packet Interface. Defines a set of commands supported through the ATA-2 interface for peripherals other than hard drives, such as CD-ROM, DVD-ROM, and tape drives.

Average Access Time

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

Average Seek Time

The average time it takes for the read/write head to move to a specific location. To compute the average seek time, divide the time it takes to complete a large number of random seeks by the number of seeks performed.


To make a copy of a file, group of files, or the entire contents of a hard disk ? either for archiving purposes or for safeguarding valuable files from loss should the active copy be damaged or destroyed.

Bad Block

A disk sector that can no longer be used for data storage, usually due to media damage or imperfections.


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


A copy of a file, directory, or volume on a separate storage device from the original, for the purpose of Recovery in case the original is accidentally erased, damaged, or destroyed.

A block (usually the size of a sector) that cannot reliably hold data because of a media flaw or damaged format markings.

This is the acronym for Basic Input/Output System. Your BIOS runs at startup, configures devices, and then boots the operating system. Because the BIOS is so integral to getting your computer started, it's stored on a separate ROM chip, not your hard drive, to isolate it from crashes.


Abbreviation for binary digit. A binary digit may have one of two values - 1 or 0. This contrasts with a decimal digit, which may have a value from 0 to 9. A bit is one of the logic 1 or logic 0 binary settings that make up a byte of data.


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.)


To start up your computer. Because the computer gets itself up and going from an inert state, it could be said to lift itself up "by its own bootstraps" -- this is where the term 'boot' originates.

Boot Disk

The magnetic disk (usually a hard disk) from which an operating system kernel is loaded (or "bootstrapped"). MS-DOS and Microsoft ? Windows? can be configured (in the BIOS) to try to boot off either floppy disk or hard disk, in either order (and on some modern systems even from CD or other removable media). A special floppy boot disk (often called a System Rescue Disk) can be created that will allow your computer to boot even if it cannot boot from the hard disk.

Boot Record

Once the BIOS determines which disk to boot from, it loads the first sector of that disk into memory and executes it. Besides this loader program, the Boot Record contains the partition table for that disk. If the Boot Record is damaged, it can be a very serious situation!

Boot Sector

See Boot Record.


To load and initialize the operating system on a computer. Often abbreviated to boot.


An area of RAM reserved for temporary storage of data that is waiting to be sent to a device.

Buffer overflow

A type of attack aimed at a common flaw in the way software is written (particularly in the very common programming language C).

Buffer overflows are best explained by way of an example. Let's say a given application includes an input field - it asks each visitor to your website to type in their password. The application sets aside a certain amount of memory (a buffer) to hold that visitor's answer. If the application isn't written correctly, the visitor might be able to input a bunch of gibberish that would fill up the available buffer space, and then "spill over" outside the buffer. Clever attackers include system commands in that spill-over, and the computer may execute those commands since the input is no longer going into the password buffer.

Buffer Under-Run

Occurs when the system cannot keep up a steady data stream to the CD recording software. The CD recorder itself has a buffer that is constantly filled with data in the event of a system slowdown or interruption. If the buffer is emptied before the system can recover, a buffer under-run occurs.


A term used for an electronic device in which a number of elements are wired together with a single wire in such way that all the elements can use the same wire to transmit information to other devices on it. Buses are used internally in computers and used to attach computers to peripherals. Only devices addressed by the signals pay attention to them; the others discard the signals.


A sequence of adjacent binary digits that the computer considers a unit. A byte consists of 8 bits.

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.


Specialized RAM used to optimize data transfers between system elements with different performance characteristics.


The amount of data that a disk drive can store after the drive has been formatted. Most disk drive companies calculate disk capacity based on the assumption that ? 1 megabyte = 1024 kilobytes and 1 gigabyte=1024 megabytes.


An acronym for re-writable CD technology whose media can be written to and erased approximately 1,000 times before failure. Standard 74min CD-RW media can hold up to 500MB when formatted for fixed-length packet writing.

Central Processing Unit (CPU)

The main processing chip of a computer. The CPU interprets and executes the actual computing tasks, and has the ability to transfer information to and from other resources over the computer's main data-transfer path, the bus.

Clean Room

An environmentally controlled dust-free assembly or repair facility in which hard disk drives are assembled or can be opened for internal servicing.


A hard disk term that refers to a group of sectors, the smallest storage unit recognized by DOS. On most modern hard disks, four 512-byte sectors make up a cluster, and one or more clusters make up a track.


A part of the motherboard that maintains system variables in static RAM. It also supplies a real-time clock that keeps track of the date, day and time. CMOS Setup is typically accessible by entering a specific sequence of keystrokes during the POST at system start-up.

Cold Boot

Starting or restarting a computer by turning on the power supply. See also warm boot.


A device that transfers information between the computer and peripheral devices. The controller (or "control unit") acts as a traffic manager.

Corrupt Data

Data that has been changed in such a way that it can no longer be used or accessed. Data is most often corrupted during an improper system shutdown (power or disk failure) when good data is overwritten with random characters, causing the data to become unreadable.


A person who enters a target computer system without permission. The motivation behind the trespassing may be malicious or based on curiosity. Altruistic crackers might notify the sysadmin of the vulnerabilities they discover.


A sudden, usually drastic failure. Can be said of the operating system or a particular program when there is a software failure. Also, a disk drive can crash because of hardware failure.


Acronym for Cyclic Redundancy Check. The CRC is used to verify data block integrity. In a typical scheme, 2 CRC bytes are added to each user data block. The 2 bytes are computed from the user data, by digital logical chips. The mathematical model is made up of polynomials with binary coefficients.

When reading back data, the CRC bytes are read and compared to new CRC bytes computed from the read back block to detect a read error. The read back error check process is mathematically equivalent to dividing the read block, including its CRC, by a binomial. If the division remainder is zero, the data is error free.


A coding method in which data is encrypted (translated into an unreadable format) and then ecrypted (translated back into a readable format by someone with a secret key) using an algorithm. Cryptography is used to send or store information securely.


The cylindrical surface formed by identical track numbers on vertically stacked discs. At any location of the head positioning arm, all tracks under all heads are the cylinder. The cylinder number is one of the three address components required to find a specific address. The other two are head number and sector number.

Data Recovery

The salvaging of data stored on damaged media, such as magnetic disks and tapes.

data recovery is associated with the process of regaining any damaged or corrupted computer data that was stored on a disk, drive or tape. Corrupted data can occur due to a variety of damage such as fire, water, magnetic damage or just due to errors, both mechanical and operator. Data recovery specialists and software can help recover any data that is still available.

Data Safe

A physical safe that should be fire and tamper-resistant used for secure storage of mission-critical software and data files.


As modern file systems are used and files are deleted and created, the total free space becomes split into smaller non-contiguous blocks. Eventually new files being created, and old files being extended, cannot be stored each in a single contiguous block but become scattered across the file system. This degrades performance as multiple seek operations are required to access a single fragmented file.

Defragmenting consolidates each existing file and the free space into a contiguous group of sectors. Access speed will be improved due to reduced seeking. A nearly-full disk system will fragment more quickly. A disk should be defragmented before fragmenting reaches 10%.

Denial-of-Service Attack (DoS)

An attack in which a mail server, Web server or even telephone system is purposely overloaded with phony requests so that it cannot respond properly to valid ones.


A list of file names and locations of files on a disk.


A circular metal platter or with magnetic material on both sides that stores data. Disks are rotated continuously so that read/write heads mounted on movable or fixed arms can read or write programs or data to and from the disk.

Disk Cache

A portion of a computer's RAM set aside for temporarily holding information that has been read from a disk. The disk cache does not hold entire files as does a RAM disk, but information that has either been recently requested from a disk or has previously been written to a disk.

Disk Drive

The motor that actually rotates the disk, plus the read/write heads and mechanisms.


Stands for direct access memory. DMA is a fast way of transferring data within a computer. Most devices require a dedicated DMA channel (so the number of DMA channels that are available may limit the number of peripherals that can be installed).


Disk Operating System. Usually used as an abbreviation for MS-DOS, a micro-computer operating system developed by Microsoft.


Time during which a system is unavailable for use due to scheduled maintenance or unexpected service disruptions (crashes).

Drive Array

A storage system composed of several hard disks. Data is divided among the different drives for greater speed and higher reliability.


Acronym for Error Correction Code. The incorporation of extra parity bits in transmitted data in order to detect errors that can be corrected by the controller.


Enhanced IDE, also called Fast ATA or Fast IDE; a connection standard that's faster than IDE and cheaper than SCSI.

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.


The disk-partitioning program used in DOS and several other operating systems to create the master boot record and allocate partitions for the operating system's use.

Fibre Channel

A technology for transmitting data between computer devices at data rates from 100 to 400 MBps over optical fiber or copper. Fibre Channel is optimized for connecting servers to shared storage devices and for interconnecting storage controllers and drives.

File Allocation Table (FAT)

The operating systems use FAT to keep track of which clusters are allocated to which files and which are available for use.


FireWire (also referred to as IEEE1394 High Performance Serial Bus) is a very fast external bus that supports data transfer rates of up to 800 Mbps. It is similar to USB. It preceded the development of USB when it was originally created in 1995 by Apple. FireWire devices can be connected and disconnected any time, even with the power on. When a new FireWire device is connected to a computer, the operating system automatically detects it and prompts for the driver disk.


Software stored in read-only memory (ROM) or programmable ROM (PROM). Easier to change than hardware but harder than software stored on disk. Firmware is often responsible for the behavior of a system when it is first switched on.

Flying Height

The distance between the read/write head and the disk surface, made up of a cushion of air that keeps the head from contacting the media


A DOS command that records the physical organization of tracks and sectors on a disk.


The state of having a file scattered around a disk in pieces rather than existing in one contiguous area of the disk. Fragmented files are slower to read than unfragmented files.


This is a user account that is not associated with an actual person (often an account of an employees who left a company). This can be utilized as an anonymous account for malicious activities. In some cases, the ghost account can also be associated with a payroll account for embezzlement purposes.

Gigabyte (Gb)

A unit of measure consisting of one billion bytes (one thousand megabytes).

Hard Disk

A mass storage device that transfers data between the computer's memory and the disk storage media. Hard disks are rotating, rigid, magnetic storage disks. (Also called a hard drive.)

Hard Drive

An electromechanical device used for information storage and retrieval, incorporating one or more rotating disks on which data is recorded, stored and read magnetically.


Acronym for head disk assembly, typically a sealed unit.


The tiny electromagnetic coil and metal pole used to create and read back the magnetic patterns on the disk. Also known as the read/write head.

Head Actuator

In a disk drive, the mechanism that moves the read/write head radially across the surface of the platter of the disk drive.

Head Crash

Damage to a read/ write head and magnetic media, usually caused by sudden contact of the heads with the disk surface. Head crash also can be caused by dust and other contamination inside the HDA.

High Level Formatting

Formatting performed by the operating system's format program (for example, the DOS FORMAT program). Among other things, the formatting program creates the root directory, file allocation tables, and other basic configurations.

High-Level Format

A high-level format must be performed (with EZ-Drive or the Format command) on a new hard drive (in most cases) 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.

I/O (Input/Output)

Input is the data flowing into your computer. Output is the data flowing out. I/O can refer to the parallel and serial ports, keyboard, video display, and hard disks and floppy disks.


IDE is a standard interface for connecting a hard disk drive or CD ROM to a personal computer. IDE which stands for Integrated Drive Electronics is an early version of the AT Attachment (ATA) specification. The name IDE was due to the hard drive controller being integrated on the drive itself rather than a separate controller on the host computer.

Enhanced IDE (EIDE) is an extension to the original standard allowing support for drives larger than 528Mb up to 8.4Gb.

The terms IDE and EIDE can be used interchangeably with ATA


A hardware or software protocol, contained in the electronics of the disk controller and disk drive that manages the exchange of data between the drive and computer. The most common interfaces for small computer systems are AT (IDE) and SCSI.


Stands for interrupt request. IRQ is the name of the hardware interrupt signals that PC peripherals (such as serial or parallel ports) use to get the processor's attention. Since interrupts usually cannot be shared, devices are assigned unique IRQ addresses that enable them to communicate with the processor. Peripherals that use interrupts include LAN adapters, sound boards, scanner interfaces, and SCSI adapters.


A plastic plug containing a metal bridge that completes a circuit; when placed over different pins on a card, a jumper changes the parameters (for example, forcing a hard drive to be secondary storage rather than a boot disk).

Kilobyte (Kb)

A unit of measure consisting of 1,024 bytes.

Landing Zone

A non-data area on the disk's inner cylinder where the heads can rest when the power is off.

LBA (Logical Block Addressing)

A method of addressing the sectors on a drive. Addresses the sectors on the drive as a single group of logical block numbers instead of cylinder, head and sector addresses. It allows for accessing larger drives than is normally possible with CHS addressing.

Logical Drive

A logical drive is a section of the hard disk that appears to be a separate drive in a directory structure. You create logical drives on the extended partition of a hard disk. While 26 letters exist for logical drives, the first three are reserved. A and B are reserved for floppy disk drives, and C is reserved for the first primary DOS partition. Therefore, you can create up to 23 logical drives on your extended partition. Logical drives are usually used to group directories and files.

Low Level Format

The first step in preparing a drive to store information after physical installation is complete. The process sets up the handshake between the drive and the controller.


The Master Boot Record (MBR) is a small program that is executed when the computer is first turned on. Typically, the MBR can be found on the first sector of a disk. The MBR first reads the disk's partition table to determine which partition is used to load the operating system. The MBR then transfers control to this partition's "boot sector" to continue the process. Loading the operating system is called "booting" the computer.

Megabyte (Mb)

A unit of measurement equal to 1 million bytes or 1,024 kilobytes or 1,048,576 bytes.

Megahertz (MHz)

A measurement of frequency in millions of cycles per second.


Master File Table. A file that contains the records of every other file and directory in an NTFS-formatted hard disk drive. The operating system needs this information to access the files.


A popular term for RAID-1. A method of creating disc-fault tolerance by redundantly storing information on a pair of drives.


Acronym for mean time between failures. Reliability rating indicating the expected failure rate of a product in power on hours (POH).

MTBF (Mean Time Between Failure)

A measure of reliability. The MTBF is the number of failures divided by the number of hours the component has operated. The longer the time span between failures, the more reliable the device.


Acronym for mean time to repair. The average time it takes to repair a drive that has failed for some reason.


NT File System. NTFS was created to provide a more reliable operating system, compared to the FAT file system.

Operating System

A program which 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 may run software applications. The goal of the operating system is to enable the user to conveniently use the computer's resources such as the CPU, memory, storage devices and printers.


A logical section of a disk. Each partition normally has its own file system.

Partition Boot Sector

On NTFS or FAT file systems, the partition boot sector is a small program that is executed when the operating system tries to access a particular partition. On personal computers, the Master Boot Record uses the partition boot sector on the system partition to determine file system type, cluster size, etc. and to load the operating system kernel files. Partition boot sector is the first sector of the partition.

Partition Table

A 64-byte data structure that defines the way a PC's hard disk is divided into logical sectors known as partitions. The partition table describes to the operating system how the hard disk is divided. Each partition on a disk has a corresponding entry in the partition table. The partition table is always stored in the first physical sector of a disk drive.


Method for creating a logical file structure that the operating system can access. Method for dividing an area on the disc drive for use by more than one disc operating system, or for dividing large disc drives into areas which the file allocation table (FAT) can deal with when in use.


A device that performs a function and is external to the system board. Peripherals include displays, disk drives, and printers.


A disk made of metal (or other rigid material) that is mounted inside a fixed disk drive. Most drives use more than one platter mounted on a single spindle (shaft) to provide more data storage surfaces in a smaller area.


Interface between components of a computer system; can be internal or external, in SCSI, EIDE, IDE, and other varieties.


A method of containing viruses that a system is unable to repair. Infected files are removed and enclosed in a quarantine area ? they can no longer be used by any applications. It may be possible for a user to manually repair and extract data from the file.


RAID is an acronym for redundant array of inexpensive drives (or disks) also known as redundant array of independent drives (or disks) and is a type of storage configuration which uses two or more drives for fault tolerance, performance, throughput or capacity. In its most simple form RAID combines two or more hard disks to form a single logical storage unit. There are a number of different RAID levels helow is a beief description of the most common:-

RAID 0 - Striped: Data is spread across two or more disks providing increased performance but no fault tollerance. If one disk becomes unavailable the whole RAID array is lost.
RAID 1 - Mirrored: Data is duplicated across two or more hard disks therefore increasing the fault tollerance. If one disk goes down the data is available on the second disk.
RAID 5 - Striped with Distributed Parity: Distributed parity requires all but one drive to be present to operate; drive failure requires replacement, but the array is not destroyed by a single drive failure.


Acronym for random access memory. An integrated circuit memory chip that allows information to be stored and retrieved by a microprocessor or controller.

Ribbon Cable

A flat cable containing numerous wires, used to connect components within the computer casing.


Acronym for run length limited. A method used on some hard disks to encode data into magnetic pulses. RLL requires more processing, but stores almost 50 percent more data per disk than the older MFM (modified frequency modulation) method.

ROM (Read-Only Memory)

The memory chip(s) that permanently store computer information and instructions. Your computer's BIOS (basic input/output system) information is stored in a ROM chip.


RPM is a measurement of how fast a hard disk's platters are spinning (in revolutions per minute). The faster the spin rate, the less time it takes for the drive to read or write a given amount of data.


A processor-independent standard for system-level interface between a computer and intelligent devices including hard disks, floppy disks, CD-ROM, printers, scanners, etc.


A sector is a section of track whose size is determined by formatting. When used as an address component, sector and location refer to the sequence number of the sector around the track. Typically, one sector stores one user record of data. Determining how many sectors per track to use is dependent on the system type, the controller capabilities, and the drive encoding method and interface.

Seek Time

A measure (in milliseconds) of how fast the hard drive can move its read/write heads to a desired location.


The second drive in a dual drive combination.

SMART (Self Monitoring Analysis And Reporting Technology)

SMART is an industry standard compatible with most modern hard drives and employs predictive diagnostics and analysis to help foresee a drive failure before it happens.


The drive's center shaft, on which the hard disk platters are mounted.

System Rescue Disk

See Boot Disk

System-Level Interface

A connection between the hard disk and its host system that puts control and data-separation functions on the drive itself (and not on the external controller). SCSI and IDE are system-level interfaces.

Terabyte (Tb)

A Terabyte = 1,099,511,627,776 bytes (or approximately one trillion bytes). A terabyte is equivalent to 1,000 gigabytes or 1,000,000 megabytes


The circular path traced across the spinning surface of a disk platter by the read/write head inside the hard disk drive. The track consists of one or more clusters.

Transfer Rate

The speed at which a disk drive can transfer information between its platters and the CPU. The transfer rate is typically measured in megabytes per second, megabits per second, or megahertz.

Trojan Horse

A malicious program that disguises itself as a beneficial or entertaining program but that actually damages a computer or installs code that can counteract security measures (perhaps by collecting passwords) or perform other tasks (such as launching a distributed denial of service attack). Unlike a computer virus, a Trojan horse does not replicate itself.

Ultra ATA/100

Ultra ATA/100 or Ultra DMA/100 is an extension of the current Ultra ATA/66 interface. This new high-speed interface has the capability of 100 Mbytes/sec transfer rate and maximized disk performance under the current PCI local bus environment.

Unformatted capacity

The total number of usable bytes on a disk, including the space that will be required later to record location, boundary definitions, and timing information.

USB (Universal Serial Bus)

A serial bus with a bandwidth of 1.5 megabits per second (Mbps) for connecting peripherals to a microcomputer. USB can connect up to 127 peripherals, such as external CD-ROM drives, printers, modems, mice, and keyboards, to the system through a single, general-purpose port. This is accomplished by daisy chaining peripherals together. USB supports hot plugging and multiple data streams.

Utilities Program

A program designed to perform maintenance work on a system or on system components, e.g. a storage backup program, a disk and file recovery program, or a resource editor.


A malicious program that replicates itself and may cause damage to a computer system by attacking or attaching itself to boot information, another program or a document that uses macros.

Virus Scanner

Software that is used to scan for and eradicate computer viruses, worms, and Trojan horses.


A portion of a physical disk that functions as though it were a physically separate disk.

Warm Boot

Rebooting a system by means of a software command as opposed to turning the power off and on. See also cold boot.

Winchester Disks

Former code name for an early IBM hard disk model. Sometimes still used to refer to hard drives in general.


A program that can replicate and send itself between computer systems. A worm can cause damage by itself or act as a delivery agent for a virus.