Definitions Of Technical Data Storage Terms

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Glossary of Terms

Append: When data is written after previously recorded data, as opposed to overwriting the previously recorded data. Useful in applying audit trails in file-by-file backup.

Archive: Long-term on- and/or off-site storage.

Backup: copying information from a hard disk onto another data storage medium (e.g., Travan minicartridges)

Bit: This is the smallest logical unit that can be recorded on the data cartridge and represents the binary value of either one or zero.

Block: A block consists of a number of bytes. An example of a block format is: preamble, data block marker, user data, block address, CRC, postamble. Block sizes vary, but a block size of either 512 or 1024 user data bytes is commonly used.

BOT: Beginning Of Tape

BPI: Bits per inch. The number of data bits recorded per inch of tape.

Byte: Consists of eight bits and represents one character of information.

Compression: (see Data Compression)

CRC: Cyclic Redundancy Check. A complex mathematical method used to check that the data written to tape is error-free.

Data Block Marker: This identifies the start of user data in a block.

Data Cartridge: A durable tape cassette used to store computer data.

Data Compression: Permits increased storage capacities using a mathematical algorithm that reduces redundant strings of data; can be performed by software or hardware.

Data Integrity: How good a system is at storing error-free data.

DataCare: A program of quality service and support for Travan minicartridges

Density: The measure of how much data is stored in a given length of tape; usually expressed in Bits Per Inch (BPI)

ECC: Error Correction Code. A mathematical algorithm used to correct errors should they occur.

Edge Seek: A method of using the recording head to detect the edge of tape and then to reference the tracks from the edge of tape, thus assuring the tracks are positioned accurately.

EOT: End Of Tape.

Erase: To remove previously-written data by randomizing the magnetic orientation of the media.

Error: Loss of magnetic signal strength to a degree that data is uninterpretable.

EW: Early Warning. A way that the data cartridge indicates to the drive that the end of the tape is approaching. Technically, the first hole in the EOT hole pattern. This allows drive electronics to take the appropriate actions.

Files: One or more recorded blocks of data

File Mark: A marker used to indicate the end of a file.

File-by-File Backup: A method of backup in which each file is stored separately and sequentially. Extremely useful if you need to restore or interchange a single file.

Flux Transition: A change in the magnetic state which can be interpreted to represent a data bit on tape.

Format: The definition of how data is written to the tape; it defines things such as the number and position of tracks, number of bits per inch and the recording code to be used.

Form Factor: The overall size (width) of the data cartridge drive. If the drive is a 5-1/4" form factor this means that the drive is the same size as a 5-1/4" diskette drive and uses the same fixing points. The same principle applies with the 3.5" format, where a 3.5" diskette drive may be exchanged for a 3.5" data cartridge drive in your computer.

FRPI: Flux Reversals Per Inch. The number of flux changes per inch of tape. This may or may not be equal to the number of bits per inch stored, depending on the recording code in use.

FTPI: Flux Transitions Per Inch. Same as FRPI.

Full Height: Indicates that the data cartridge drive is the same height as an equivalent full height diskette drive (approximately 3.25").

GB: Gigabyte = 1,000 megabytes = 1 billion bytes

GCR: Group Code Recording. A data encoding method often used on data cartridge drives. The code combines high data density with relative ease of decoding.

Half Height: Indicates that the data cartridge drive is the same height as an equivalent half height diskette drive (approximately 1.6").

Headers: Blocks of data written at the beginning of cartridges or files that contain specific identification information.

Hierarchical Storage Management (HSM): Automatically and transparently migrates files to tape when they have not been accessed for a defined period of time.

Infinite Disk: A software product manufactured by Cheyenne.

Initialize: To retension and read or write header blocks before a data cartridge is used.

Interchange: To remove a data cartridge from one drive and read the data on another data cartridge drive.

Interface: The physical and electrical method of connecting to a data cartridge drive system (the plug on the back).

Internet Downloading: Receiving data from the Internet.

KB: Kilobyte = 1,000 bytes

LP: Load Point. The physical location on the tape where data recording starts. This location is physically marked by the location of a punched hole.

MB: Megabyte = 1,000 kilobytes = 1 million bytes

MFM: Modified Frequency Modulation. A recording code used on some data cartridge drives. It is the most efficient self-clocking code, but requires good electronics to decode it.

MTBF: Mean Time Before Failure. Expected drive life before first failure.

MTTR: Mean Time To Repair. How long it takes to repair a drive.

Multimedia Files: Computer files containing audio, video or graphics.

Off Track Retry: A method of improving data recovery under error conditions. It is often possible to recover a data error by moving the head slightly off the track center and re-reading the block.

Overwrite: A method of overwriting data on a tape without first erasing it.

PE: Phase Encoding. A method of coding data; it has the advantage of being very reliable and easy to decode, but it is not particularly efficient in data density.

Postamble: A section of recorded data used to synchronize the data decoding electronics to the data stream. It occurs at the end of the data block.

Preamble: A section of recorded data used to synchronize the data decoding electronics to the data stream. It occurs at the start of the data block.

QIC: Quarter-Inch Cartridge Drive Standards, Inc. A group of drive and media manufacturers and interested parties that submit development standards for 1/4-inch data cartridge drives, cartridges, interfaces, etc. to standards-making organizations. An example of QIC standard nomenclature is QIC-80.

Random Access: The ability to access any particular block by going directly to it. Disk devices are random access devices.

Read After Write: A method of ensuring that data written to tape is correct by immediately reading the tape on a read head placed just after the writing head.

Reference Burst: A number of flux transitions written at the beginning of the tape to indicate the center line of the tape. This allows the read head of the drive to align itself correctly and improves the data integrity of the drive.

Restore: To read information on a data cartridge in order to replace the data that was lost from a hard disk.

Retension: The most important thing to do when you first insert a data cartridge into the drive. This ensures that the tape in the cartridge is correctly tensioned and will give you the optimum head-to-tape contact for error-free performance. Retensioning is winding the tape from the beginning of tape (BOT) to the end of tape (EOT), or EOT to BOT.

RLL: Run Length Limited. A family of codes used to encode data. They have the feature that the number of zero or one bits is limited to a certain value. GCR is a RLL code.

SCSI: Small Computer Systems Interface. This is fast becoming the dominant interface in the disk and data cartridge marketplace.

Search: A method of finding a particular data file without having to read all the preceding data. Often done at a different speed than reading and writing. Usually applies to start/stop drives.

Sequential Device: A device that has to read each data block sequentially as opposed to a random access device.

Start/Stop: A data cartridge drive that is capable of stopping and starting before and after each data block written or read from tape.

Streamer: A data cartridge drive that writes or reads blocks without stopping between blocks.

Tape-It: A software product manufactured by PG Soft.

Tape Mark: A unique data block used to separate data files or volumes of data.

Third Height: Drive height which is 1/3 the height of a full height drive (approximately 1").

Track: A linear area of tape written along the tape length.

Travan: A high-capacity minicartridge technology developed by Imation Corporation (formerly a division of 3M Company)

Underrun: When a streaming drive runs out of data to be written to tape, it has to stop and reposition the tape. This is what happens when your processor is too slow to keep up with the streamer.

User Data: Data recorded by the user. User data is differentiated from other information recorded by either the drive or formatter.

Verify: The action of comparing the data written to tape with the data on the disk. Verification provides an additional confidence check.

Volume: A volume consists of a number of files.

Volume Label: A data block written at the front of a volume to identify it.