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IBM 728

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Magnetic tape drive used on the SAGE AN/FSQ-7 computer
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The IBM 728 was an IBM 7 series magnetic tape drive. It was used on the SAGE AN/FSQ-7 computer. It was physically similar to the IBM 727, but with significantly different specifications.

Tracks 6 Data, 1 synchronization
char/inch 248 char/inch
Words 6 chars (32 data bits, 1 odd parity bit, 3 end of file bits)
word/inch 41.33 word/inch
End of record gap 0.75 inch - 186 chars - 31 words
Tape speed 75 inch/s
Rewind speed 500 inch/s (average)
Transfer rate 18,750 char/s - 3,125 word/s
Start time 5 ms
Stop time 5 ms
Width of tape 1/2 inch
Length of reel 2,400 ft (730 m)
Composition Mylar or cellulose acetate base
            Tape Word Bit Positions
            ----------------------------->   Tape travel
            LS   L6   L12  R2   R8   R14
            L1   L7   L13  R3   R9   R15
            L2   L8   L14  R4   R10  P
            SYN  SYN  SYN  SYN  SYN  SYN
            L3   L9   L15  R5   R11  EOF
            L4   L10  RS   R6   R12  EOF
            L5   L11  R1   R7   R13  EOF
            ----------------------------->   Tape travel

References

  1. Faust, Daniel (2008). IBM 728 Magnetic Tape Drive (inkjet print of photograph). The Metropolitan Museum of Art.
Magnetic-tape data storage formats
Linear
Wide (19–25.4 mm)
Half inch (12.7 mm)
Eight millimeter (8 mm)
Quarter inch (6.35 mm)
"Eighth" (0.15) inch (3.81 mm)
Stringy (1.58–1.9 mm)
Helical
Three quarter inch (19 mm)
  • Sony DIR (19xx)
  • Ampex DST (1992)
Half inch (12.7 mm)
Eight millimeter (8 mm)
Four millimeter (3.81 mm)
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