Magnetic Tape Systems

• Used to store large amount of data.• Same technology of Magnetic Disk.• Magnetic film is deposited on a very thin 0.5

or 0.25 inch wide plastic tape.• 7 or 9 bits are recorded in parallel across the

width of tape.• A separate Read/Write head is provided for

each bit position on the tape, in order to read or write all bits of a character parallel.

File MarkRecord Record

Gap

File

7 or 9 bits

Organization of Data on Magnetic Tape

• Data on the tape are organized in the form of records separated by gaps.

• Tape motion is stopped when a record gap is under the Read/Write heads.

• Group of related records called a FILE. Which is used to help users organize large accounts of data.

• The beginning of a file is identified by a file mark which is a special single or multiple character record, usually proceeded by a gap longer than the inter record gap.

• The first record following a file mark can be used as a header or Identifier for this file allowing the user to search a tape containing a large number of files for a particular file.

Control Commands by a Controller

• Rewind Tape• Rewind and unload tape.• Erase Tape.• Write tape mark.• Forward space one record.• Backspace one record.• Forward space one file• Backspace one file.

Method of formatting and using tapes

Two methods:1. The records are variable in length.

Advantages: Tape can be used efficiently.

Disadvantages: Not permit updating & overwriting

2. The records are of Fixed Length

Advantages: Possible to update records

Applications of Magnetic tapes: storage of data. back up information.

Cartridge Tape system• 8mm video format tape housed in a cassette.• Capacity 2-5 GB• Data transfer rate--? Few hundred KBPS• Read/Write helical scan system