IBM 727

An IBM 704 mainframe with IBM 727 tape drives on the left. (image courtesy of LLNL)

Half-inch tape reel with write protect rings

The IBM 727 Magnetic Tape Unit was announced for the IBM 701 and IBM 702 on September 25, 1953. It became IBM's standard tape drive for their early vacuum tube era computer systems. Later vacuum tube machines and first-generation transistor computers used the IBM 729-series tape drive. The 727 was withdrawn on May 12, 1971.

The tape had seven parallel tracks, six for data and one to maintain parity. Tapes with character data (BCD) were recorded in even parity. Binary tapes used odd parity. Aluminum strips were glued several feet from the ends of the tape to serve as logical beginning and end of tape markers. Write protection was provided by a removable plastic ring in the back of the tape reel.

tracks	6 data, 1 parity
chars/inch	200 characters/inch
Tape speed	75 inches/second
Rewind speed	500 inches/second (average)
Transfer rate	15,000 characters/second
Start time	5 milliseconds
Stop time	5 milliseconds
Width of tape	1/2 inches
Length of reel	2,400 feet
Composition	PET film (Mylar) or cellulose acetate base

Sources

IBM 727 Magnetic tape unit

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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