A report on 9-track tape, Magnetic-tape data storage and Group coded recording

The 1⁄2 inch (12.7 mm) wide magnetic tape media and reels have the same size as the earlier IBM 7-track format it replaced, but the new format has eight data tracks and one parity track for a total of nine parallel tracks.

Tape was an important medium for primary data storage in early computers, typically using large open reels of 7-track, later 9-track tape.

The first, used in 6,250 bpi magnetic tape since 1973, is an error-correcting code combined with a run length limited (RLL) encoding scheme, belonging into the group of modulation codes.

Various recording methods have been employed during its lifetime as tape speed and data density increased, including PE (phase encoding), GCR (group-coded recording) and NRZI (non-return-to-zero, inverted, sometimes pronounced "nur-zee").

Group coded recording was first used for magnetic tape data storage on 9-track reel-to-reel tape.

Common 7-track densities started at 200 characters per inch (CPI), then 556, and finally 800; 9-track tapes had densities of 800 (using NRZI), then 1600 (using PE), and finally 6250 (using GCR).