IBM 726

The IBM 726 dual magnetic tape reader/recorder for the IBM 701 was announced on May 21, 1952. Unlike later IBM 7 track drives, the 726 could read backwards as well as forwards.

The tape had seven parallel tracks, six for data (called a copy group, not a character) and one to maintain parity. Tapes were recorded in odd parity, to ensure at least one bit transition per copy group as well as for error checking. ^[1]

The 726 concurrently handled two reels of tape, and there were two 726 units in an IBM 701 system. ^[2]

Tracks	6 Data, 1 parity
Copy groups/inch	100 copy groups/inch
Tape speed	75 Inches/sec
Transfer rate	7 500 copy groups/sec
End of record gap	1 Inch - 100 chars - 16.67 words
Start time	10 ms
Stop time	10 ms
Width of tape	1/2 inch
Length of reel	1 200 feet
Composition	Cellulose acetate base

References

Magnetic tape data storage formats

Linear

Wide (19 - 25.4 mm)	TX-2 Tape System (1958) IBM 7340 (1961) LINCtape (1962) DECtape (1963)

Half inch (12.7 mm)	UNISERVO (1951) IBM 7 track (1952) 9 track (1964) IBM 3480 (1984) DLT (1984) IBM 3590 (1995) T9840 (1998) T9940 (2000) LTO Ultrium (2000) IBM 3592 (2003) T10000 (2006)

Eight millimeter (8 mm)	Travan (1995) IBM 3570 MP (1997) ADR (1999)

Quarter inch (6.35 mm)	QIC (1972) SLR (1986) Ditto (1992)

"Eighth" (0.15) inch (3.81 mm)	KC standard, Compact Cassette (1975) HP DC100 (1976) Tarbell Cassette Interface (1976) Commodore Datasette (1977) DECtape II (1979)

Stringy (1.58–1.9 mm)	Exatron Stringy Floppy (1979) ZX Microdrive (1983) Rotronics Wafadrive (1984)

Helical

Three quarter inch (19 mm)	Sony DIR (19xx) Ampex DST (1992)

Half inch (12.7 mm)	Redwood SD-3 (1995) DTF (19xx) SAIT (2003)

Eight millimeter (8 mm)	Data8 (1987) Mammoth (1994) AIT (1996) VXA (1999)

Four millimeter (3.81 mm)	DDS/DAT (1989)

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