Digital Storage Research Center

ATA (Advanced Technology Attachment)
A disk drive interface standard for IDE (Integrated Drive Electronics). This is a standard for storage devices, letting the attachment act as if it were a hard drive on the system. Any ATA-compatible media can be read by an ATA device.

Average Access Time
The time (in milliseconds) that a disk drive takes to find the right track in response to a request (the seek time), plus the time it takes to get to the right place on the track (the latency).

Backup
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 original 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.

BIOS (Basic Input/Output System)
A collection of computer routines that control peripherals, such as disk drives.

Bit
A binary digit is the smallest piece of information that can be recognized and processed by a computer. A bit is either 0 or 1 and can form larger units of information called bytes (8 bits).

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

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

Cache
High-speed RAM used as a buffer between the CPU and a hard drive. The cache retains recently gathered information to speed up subsequent access to the same data. When data is read from or written to a disk, a copy is saved in the cache, along with the associated disk address. The cache monitors the addresses of subsequent read operations to see if the required data is already in the cache. If it is, the drive returns the data immediately. If it is not in the cache, then it is retrieved from the disk and saved in the cache.

Capacity
The amount of data that a disk drive can store after the drive is formatted. Most disk drive companies calculate disk capacity based upon 1 megabyte = 1,000 kilobytes and1 gigabyte = 1,000 megabytes.

Cluster
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.

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

Central Processing Unit (CPU)
The CPU is the main processing chip of a computer. It 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.

Data Recovery
Data recovery is the procedure used to recover data from a variety of media and operating systems that is lost by either hardware failure, human error, software bugs, a virus or a natural disaster.

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

Disk
A circular metal platter 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 was read from a disk. The disk cache does not hold entire files as does a RAM disk, but information that was either recently requested from a disk or was previously written to a disk.

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

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

File Allocation Table (FAT)
The operating system uses a file allocation table to keep track of which clusters are allocated to certain files and which clusters are available for 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.

Firewire®
FireWire (IEEE1394 High Performance Serial Bus) is a very fast external bus that supports data transfer rates of up to 800 Mbps. These 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.

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

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
The hard drive is the primary storage area (the C: drive, for instance) of a computer. (Also called a hard disk.)

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

IDE
Integrated Drive Electronics, also called ATA, is a connection standard that integrates the drive's controller chip on the drive itself.

Interface
The drive interface is the "language" or protocol a drive uses to communicate with a host computer or network. The three main types of drive interfaces are ATA (IDE), SCSI and Fibre Channel. The ATA and SCSI interfaces have evolved to include many subtypes, which may or may not be backwardly compatible.

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, hard disks and floppy disks.

Kilobyte (KB)
1,024 bytes, but it is often used loosely as a synonym for 1,000 bytes and sometimes abbreviated as k (lowercase), K-byte, K or KB for kilobyte. Data transfer rates are measured in kilobytes per second, abbreviated as KBps, and count a kilo as 1,000 bytes.

Megabyte (MB)
1,048,576 bytes (1,024 times 1,024). This is used to describe the total capacity of a hard disk or the total amount of RAM. Sometimes abbreviated as Mb, M, MB or meg for megabyte.

Millisecond (ms)
1/1,000 (one-thousandth) of a second. Hard disks are rated in milliseconds and higher numbers mean slower performance.

Operating System (OS)
The operating system performs basic tasks, such as recognizing input from the keyboard, sending output to the screen, keeping track of files and directories on the disk, and controlling peripheral devices, such as disk drives and printers. PC operating systems include DOS and Windows XP, and Apple Mac operating systems include OS 9 and OS X.

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

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

Platter
A metal or other rigid material disk that is mounted inside a fixed-disk drive. Many drives consist of multiple platters mounted on the spindle to provide more data storage surfaces. Each platter may use one or both surfaces to store data.

Port
This is the interface between components of a computer system. These can be internal or external, in SCSI, EIDE, IDE and other varieties.

RAID (Redundant Array of Independent Disks)
RAID is a way of storing the same data in different places (thus, redundantly) on multiple hard disks. By placing data on multiple disks, input/output operations can overlap in a balanced way, improving performance. Since multiple disks increases the mean time between failure (MTBF), storing data redundantly increases fault-tolerance.

RAM (Random-Access Memory)
Also known as read-write memory, this is the memory used to execute application programs.

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
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.

SCSI (Small Computer System Interface)
A system-level interface designed for general-purpose applications that allows up to seven devices to be connected to a single host adapter. It uses an 8-bit parallel connection that produces a maximum transfer rate of 5Mb per second. The term is pronounced "scuzzy."

Sector
The basic storage unit on a hard disk. On most modern hard disks, sectors are 512 bytes each; four sectors make up a cluster.

Seek Time
Seek time is an average of how long a drive takes to move the read/write heads to a particular track on the disc. It includes controller overhead but does not include drive latency.

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.

Spindle
One part of a hard disk, around which the platters rotate.

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.

Track
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.

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

Universal Serial Bus (USB)
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.