IBM 729

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Private Patricia Barbeau operates an IBM 729 at Camp Smith , Hawaii (1969)
Roll of tape with reflective switching tape (start marking)
Troubleshooting an IBM 729 tape drive in the Computer History Museum as part of the IBM 1401 restoration project. Inserting a reel of magnetic tape; the system operator guides the tape with his finger until the take-up roller has captured a few revolutions of the tape to secure the tape transport. In the foreground of the picture is an IBM 1403 line printer.

The magnetic tape unit IBM 729 is an icon of magnetic tape - storage since the 1950s to mid-1960s. It is part of IBM's seven-track reel magnetic tape machine series , the series into the computer 700/7000 IBM has been used and some 1400ern. Like its predecessor, the IBM 727, the 729 ½ "(12.7 mm) tape used on 10½ " (267 mm) diameter rolls that held up to 2400 feet (730 m) of tape. In order to enable rapid acceleration of the tape and the associated quick access, tape loops were guided in long vacuum columns, which decoupled the jerky movements of the tape on the magnetic heads from the rollers, since, transferred to the rollers, these would tear the tape. The write protection was a removable plastic ring on the back of the roll.

Data format

The head records seven parallel tracks on the tape, six for data and one parity bit . Tapes in BCD format were recorded with even parity, binary recordings use odd parity. (709 Manual p.20) When switching tape Aluminum strips were glued several feet before the band ends, to have physical start and end markers on the tape. A gap of ¾ inch was left between the data blocks (records) in order to resume recording and playback at this point . The operating tape speed is 75 inches / second (IPS) (= 2.95 m / s), with a data density of 200 characters per inch, which enables a data transfer rate of 120 kbit / s. Newer models of the 729 series support 556 and 800 characters per inch (CPI) at a transfer rate of 480 kbit / s. At 200 CPI, a 2,400 foot long tape could store as much as 50,000 punch cards (over 4 million six-bit data words , or 3 Mbytes ).

The 729 series was superseded by the 9-track tape drives that were introduced with the IBM System / 360 .

Models

729 I.
The IBM 729 I was built for the IBM 709 and IBM 705 III computers and looked exactly like the IBM 727 and used electron tubes . The main innovation was the write head, which had a second gap so that the written data could be checked immediately.
729 II
The IBM 729 II was built for the computers of the IBM 7000 series and came in a new design, was completely transistorized and supported two data densities of 200 and 556 CPI.
729 III
supports up to 112.5 IPS with a data density of only 556 CPI.
729 IV
supports up to 112.5 IPS and two data densities of 200 and 556 CPI.
729 V
Data density 800 CPI.
729 VI
Launched September 1961 and supports 112.6 IPS at 800 CPI.

Other series

With the IBM 7330 , IBM pushed an entry-level magnetic tape mass storage unit in the lower price segment in the 1960s. It was designed with about half the belt speed of 36 IPS.

Web links

Individual evidence

  1. ↑ (8 bits wide * 200 characters) * 75 IPS
  2. ↑ DPD chronology