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Data Storage Glossary


The Institute of Electrical and Electronics Engineers (IEEE) designation for an interface developed for easy connection to consumer devices such as video and computer peripherals.

Adapter Card

In order to connect a computer to peripheral devices, an adapter card is often required. The adapter plugs into the computer's bus, and connects the system's data path to the peripheral.


A group of disk drives that appear to a computer as a single logical unit. In order to use arrays effectively, RAID software and/or hardware is required.


A data transmission rate; the maximum amount of information (bits/second) that can be transmitted along a channel.


A set of conductors connecting the various functional units in a system.

CD-R (Compact Disc-Recordable)

A blank CD that is designed to allow data to be "written" a single time on its surface. Peripheral devices that connect to PCs enable home or office single-time recording of blank CD-Rs.

CD-RW (Compact Disc-Rewritable)

A blank CD that is designed to allow data to be written, erased, and rewritten onto a CD-RW. Rewritable capability makes CDs more versatile by mimicking the usability of floppy disks.

Data Caching

Temporary storage of new write data or high-demand read data in solid-state memory in order to accelerate performance. The cached data is later overwritten with newly cached data once it is either written to disk or deemed to be of low demand.

Data Path

Digital information can be transmitted in different sized "paths" within a computer. Generally, the wider the data path, the higher the throughput performance. Today, the most standard data path width is 32-bit, though new products are entering the market with 64-bit paths, providing better I/O performance.

Disk Drive

Computer storage hardware that can read and write information on it.


Enhanced Integrated Drive Electronics. A low cost, limited functionality drive interface. Controlled by the ANSI X3T9.2 committee.


A type of networking technology for local area networks.

Fault Tolerance

The ability of a system to continue to perform its functions, even when one or more components have failed.

Fibre Channel

A channel/network standard that provides connectivity, distance, and protocol multiplexing.

I/O Bus

The I/O bus is where the computer connects to outside peripherals.

I/O Channel

In computer systems, I/O Channel refers to the physical interface that controls the transfer of data between the computer and peripheral devices. With SCSI, each I/O Channel is equivalent to the full functionality of a single SCSI host adapter. For example, a dual-channel SCSI host adapter is equivalent to two single SCSI host adapters.

I/O Subsystem

The combination of technologies that manage the process of moving data into and out of the main computer system. The highest performance I/O subsystems use dedicated processors to minimize the CPU's need to manage I/O, thereby allowing it to process the information that is moved to it from the I/O subsystem.


Also known as RAID 1 or duplexing (when using two host bus adapters). Full redundancy is obtained by duplicating all data from a primary disk on a secondary disk. The overhead of requiring 100% data duplication can get costly when using more than two drives.


The main printed circuit board in a system generally containing the bus, microprocessor, and chips used for controlling any internal peripherals.


The ability for the operating system to perform multiple operations at once. Windows NT Workstation is a multitasking operating system that can perform multiple I/O requests at once. SCSI and a Caching RAID coprocessor take advantage of multitasking.

Network Interface Card (NIC)

An adapter installed in a computer to provide a physical connection to a network.


When the data stream is split between several disks with an extra disk providing error protection.

PCI (Personal Computer Inter-connect)

PCI is the most common high-performance bus type. Currently, PCI uses a 32-bit wide data path, but newer PCI products are adopting a 64-bit wide data path for improved performance.


Internal or external devices connected by cable to a system.

RAID (Redundant Array of Independent/Inexpensive Disks)

A method of combining multiple disk drives into a single logical storage unit. Multiple levels of RAID provide different features. RAID Level 0 is the fastest type of RAID. It stores data across all the drives, letting users access information from multiple drives simultaneously. RAID Level 1 protects data by mirroring it on multiple drives, so performance is only slightly better than that of a single drive. RAID Level 5 does a combination of the two, providing the best overall balance.


An upgrade connector that sits on the Adaptec SCSI-equipped PC workstation motherboard, which allows upgrading the motherboard's SCSI channels to RAID.

Read-ahead Caching

A performance caching technique in which data is anticipated and read into the cache before it is actually requested.

SAN (Storage Area Network)

SANs are an evolving approach to storage, where multiple storage devices are connected to multiple servers for higher capacity, throughput, and reliability. SANs require sophisticated RAID management software and high-performance I/O connectivity.

SCSI (Small Computer System Interface, pronounced "scuzzy")

SCSI is the preferred industry standard for high-performance I/O interface. Particularly valuable in servers where one system must connect to many high-capacity storage devices without lowering the I/O speed to the slowest device.

S.M.A.R.T. (Self-Monitoring Analysis and Reporting Technology)

Drives equipped with this feature report predicted failures based on threshold values determined by the manufacturer. This allows the network manager to replace a drive before it fails.


Computers store information on a variety of devices, some inside the system, and others external to the computer. Typically, data is written to a particular kind of storage medium using a disk drive. Common media include flexible (floppy disk drive), rigid (hard disk drive), tape, or optical (CD).


Also known as RAID 0. Two or more drives store and retrieve data in parallel, accelerating performance.

Write-back Caching

A performance caching technique in which the completion of a write request is signaled as soon as the data is in cache. Actual writing to the disk occurs at a later time.

Write-through Caching

A caching technique in which the completion of a write request is not signaled until data is safely stored on disk

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