Magnetic tape - physical characteristics

A tape is a strip of iron oxide coated plastic film, which is a low cost, high storage capacity, sequential media for storing data. This page deals with how the computer works with a tape.

Traditional:

Diagrammatically, the way data is stored on a tape is as follows;

Access methods

Exercise 1: On your casette tape recorder;

• How would you find a song you wish to play ?
• How would you insert a song between two existing songs?

Exercise 2: For a data tape;

• How would you read data? How would you insert data?

QIC

• 20 - 32 parallel tracks
• Single track written to, once end of tape reached, tape reverses and writes to next outside track. This continues in a spiral until all tracks written to.
• Each track divided into blocks of 512 or 1,024 bytes
• Segments typically contain 32 blocks
• 8 blocks in a segment contain error correction codes.
• Cyclic redundancy check (CRC) appended to each block
• Directory information stored at the beginning of track 0 or on a separate track.

Ref [79]White '93

Exercise 1: Physical Data Storage - Tape File Storage
For your casette tape recorder;

How would you find a song you wish to play ?

• Rewind the tape to the start
• Play (or use a Fastforward cueing ) until the song is found.

How would you insert a song between two existing songs?

Use two tapes.

• Copy songs from the start of the existing tape until you get to the gap where you want to insert the song.
• Copy the new song onto the new tape
• Copy the rest of your original tape onto the new tape.

Exercise 2: Physical Data Storage - Tape File Storage

For tape operations,

To read any data requires;

• Rewind tape to start, then sequentially read data until portion you want is located.

To insert data,

• Two tapes required current(1) and new(2).
• Copy from start of tape 1 to where data is to be inserted, onto tape 2.
• Copy data to insert onto tape 2
• Copy rest of tape 1 to tape 2