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9-track tape

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Full-size reel of 9 track tape.

The IBM System/360, released in 1964, introduced what is now generally known as 9 track tape. The magnetic tape is 1/2 inch (12.65 mm) wide, with 8 data tracks and one parity track for a total of 9 parallel tracks. Data is stored as 8-bit characters, spanning the full width of the tape (including the parity bit). Various recording methods are used to place the data on tape, depending on the tape speed and data density, including PE (phase encoding), GCR (group code recording) and NRZI (non-return-to-zero, inverted, sometimes pronounced "nur-zee").

The standard size of a byte was effectively set at 8 bits with the S/360 and 9 track tape.

Technical details

9-track 800 NRZI and 1600 PE (phase encoding) tapes utilized a .60" inter-record gap (IRG) placed between data records to allow the tape to stop. 6250 GCR tapes used a very tight .3" IRG. 9-track tapes had reflective stickers placed near (10', 14') each end to signal beginning of tape (BOT) and end of tape (EOT) to the hardware. Nine-track tapes commonly had densities of 800, 1600, and 6250 cpi, giving approximately 20MB, 40MB and 140MB respectively on a standard 2400' tape. Signaling EOT (end of tape) with space remaining to write trailer blocks allowed support for multivolume labelled tapes.

IBM generations

IBM Model 2400 Series 3400 Series
Model numbers 2401, 2415, 2420, 2440 3410, 3420, 3422, 3440
Density (bits/in) 800, 1600 1600, 6250
Tape speed (in/s) 18.75 - 200 120 - 200
Transfer rate (B/s) 15,000 - 320,000 1,250,000
Interblock gap (in) 0.6 0.3
Rewind speed (in/s, avg.)
Start time (ms)
Stop time (ms)
Length of reel (ft) 2400 max 2400 max
Base composition Plastic Plastic

2400 Series

The 2400 Series Magnetic Tape Units were introduced with the System/360 and were the first to use 9 track tape. The dimensions of the tape and reels were identical to those used with 7 track units, such as the IBM 729. But older 7 track tapes could only be read and written on special 2400 drives equipped with 7 track read and write heads and the 7 track compatibility option.

3400 Series

The 3400 Series Magnetic Tape Units were introduced with the System/370. The primary advantages of the 3400 system were the higher data density (6250 BPI) and the introduction of the "autoloader" cartridge. Prior to the autoloader cartridge, tapes were sealed in a plastic "tape seal belt" that surrounded the reel and provided contamination protection and rack-hanging capability. The 3420's autoloader cartridge enabled the tape operator to mount the reel directly on the hub without having to remove the seal belt. This provided a significant time savings since the operator did not have to remove/replace the belt or thread the tape onto the take-up reel.

The maximum data capacity of a 2400 ft reel, blocked at 32,767 bytes and recorded at 6250 BPI was 170 megabytes. Typically, much smaller block sizes, such as 4K (4,096 bytes) were used, in which case the storage capacity of the tape was reduced by 33% to 113 megabytes.

Examples

  • Two small 1/2" tapes, front and back.
    Two small 1/2" tapes, front and back.
  • Aluminum foil stickers marked the start and end of tape.
    Aluminum foil stickers marked the start and end of tape.
  • The write protection ring prevented the tape from being written on when removed.
    The write protection ring prevented the tape from being written on when removed.

Standards

  • ANSI INCITS 40-1993 (R2003) Unrecorded Magnetic Tape for Information Interchange (9-Track, 800 CPI, NRZI; 1600 CPI, PE; and 6250 CPI, GCR)
  • ISO/IEC 1863:1990 9-track, 12.7 mm (½ in) wide magnetic tape for information interchange using NRZ1 at 32 ftpmm (800 ftpi) - 32 cpmm (800 cpi)
  • ISO/IEC 3788:1990 9-track, 12.7 mm (½ in) wide magnetic tape for information interchange using phase encoding at 126 ftpmm (3 200 ftpi), 63 cpmm (1600 cpi)
  • ANSI INCITS 54-1986 (R2002) Recorded Magnetic Tape for Information Interchange (6250 CPI, Group Coded Recording)
  • ANSI INCITS 27-1987 (R2003) Magnetic Tape Labels and File Structure for Information Interchange

Other drive manufacturers

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