Glossary of Tape Media Terms
Append - In its basic form tape technology is linear in fashion. Later technologies employ serpentine recording where the tape is written/read in multiple passes moving forward and in reverse. There are also helical scan formats, such as DDS, 8mm and AIT , which are written diagonally across the tape.
Archive - Long-term on- and/or off-site storage.
ASCII - American Standard Code Information Interchange. An ANSI standard code for transferring information from one computer language to another.
Backup - Copying information from a hard disk onto another data storage medium (e.g., tape).
Bit - Smallest amount of data that can be processed by a computer; represents the binary value of either one or zero.
Block - Consists of a specific, pre-determined number of bytes. Block sizes vary, but a block size of either 512 or 1024 user data bytes is commonly used.
BOT - Beginning of Tape. Designated by a specific mark, hole or logical means.
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.
CompacTape - A " tape format developed by DEC. It is also commonly referred to as TK50 or TK52.
Compression - (See Data Compression)
Convert - To change media or recording type from one format to another. Converting typically includes copying the data on one type of media to a different type of media.
CRC - Cyclic Redundancy Check. A complex mathematical method used to check that the data written to tape is error-free.
Data Block Marker - Identifies the start of user data in a block.
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 - Validity of recorded information.
Degausser - A machine that uses a magnetic field to remove previously-written data on tape by randomizing the magnetic orientation of the media.
Density - The amount of data stored in a given length of tape; usually expressed in bits per inch (BPI).
DLT - Digital Linear Tape. A popular " tape cartridge format developed by DEC originally as CompacTape. It iscurrently manufactured under license by Quantum.
EBCDIC - Extended Binary Coded Decimal Interchange Code. A common machine language that represents alphanumeric data.
ECC - Error Correction Code. Mathematical algorithm used to correct errors.
Edge Seek - 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 (see Degausser).
Error - Loss of magnetic signal strength to a degree that data cannot be read.
Error Correction Codes (ECC) - Onboard system codes that correct errors, in real time, without the drive having to perform retries, thus not affecting processing time.
Error Recovery Procedure (ERP) - In the event of a potential defective area of tape, the drive will stop processing data and effectively process errors by performing mechanical drive retries. This does impact processing time and may lead to a block of data being written elsewhere on the tape.
Files - One or more recorded blocks of data.
File Mark - Marker used to indicate the end of a file.
File-by-File Backup - 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 - Change in the magnetic state, which can be interpreted to represent a data bit on tape.
Format - Defines 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 - Physical size of a device; for example, the width of a 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 that may not necessarily be a flux reversal.
GB - Gigabyte = 1,000 megabytes = 1 billion bytes.
GCR - Group Code Recording. A data encoding method often used on data cartridge drives. GCR combines high data density with relative ease of decoding.
Headers - Blocks of data written at the beginning of tapes or files that contain specific identification information.
HSM - Hierarchical Storage Management. A system of ranking and storing information across a variety of device types. HSM maintains it's own catalog information outside of the normal TMC or TMS system.
Initialize - To write the Volume ID in the header before a tape is used.
Interchange - To remove a tape from one drive and read the data on another tape drive.
Interface - Hardware and software used to establish communication between a host and device.
KB - Kilobyte = 1,000 bytes
LP - Load Point. The physical location on the tape where data recording begins.
MB - Megabyte = 1,000 kilobytes = 1 million bytes.
Media Cleaning - The physical cleaning of both sides of the tapes surface. Normally done on a "Tape Cleaner" specifically designed for that particular media type.
MFM - Modified Frequency Modulation. Recording code used on floppy-interface QIC drives. It is the most efficient self-clocking code, but requires "good" electronics to decode.
MTBF - Mean Time Before Failure. Expected time before first failure.
MTTR - Mean Time To Repair. Estimated time to repair a drive.
Multimedia Files - Computer files containing audio, video or graphics.
Off Track Retry - 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.
Open Reel Tape (ORT) - A term used synonymously with 9-track tape. eMag was the last manufacturer of ORT.
Overwrite - Method of overwriting data on a tape without first erasing it.
PE - Phase Encoding. 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.
QIC - Quarter-Inch Cartridge.
Random Access - Ability to access any particular block by going directly to it. Disk devices are random access devices.
Read After Write - 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 - 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 - Retrieving information from a tape drive in order to replace data that was lost from a hard disk.
Retension - 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. The number of zero or one bits is limited to a certain value. GCR is an RLL code.
SCSI - Small Computer Systems Interface. A bus interface that enables many different kinds of devices, such as disk drives, CD-ROM drives and Tape drives, to interface with the host PC type computer.
Search - 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 - Device that reads each data block sequentially as opposed to a random access device.
Single Track Error (STE) - A loss of a recorded "bit" due to anything that causes loss of signal. Single track error performance is a direct indicator of the magnetic quality of the tape.
Start/Stop - Tape drives that are capable of stopping and starting before and after each data block written or read from tape.
Streamer - Tape drives that write or read blocks without stopping between blocks.
Tape Mark - Unique data block used to separate data files or volumes of data.
Track - Linear area of media on which data is written.
Underrun - Action that occurs when a streaming drive runs out of data to be written to tape; it stops and repositions the tape. This occurs 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 - Action of comparing the data read to data written. Verification provides an additional confidence check for data integrity.
Volume - Logical division of data. Consists of a number of files.
Volume Label - Data block written at the front of a volume to identify it.
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