IBM 7-track
| Company type | Product line |
|---|---|
| Industry | Data storage |
| Founded | 1952 |
| Founder | IBM |
| Products | IBM 726, IBM 727, IBM 728, IBM 729, IBM 7330, IBM 2400 Series magnetic tape drives |
| Parent | IBM |
IBM launched its initial magnetic-tape data storage systems in 1952, utilizing 7-track tape technology. This broad magnetic tape contained six tracks dedicated to data alongside one parity track, encoding six-bit characters with each individual bit and parity placed on separate tracks.
These large, floor-mounted tape drives incorporated vacuum columns to manage U-shaped tape loops, which facilitated rapid starting and stopping of the tape at the head interface through synchronized reel motors combined with vacuum regulation. This design enabled swift intermittent movement of the tape, often portrayed in popular culture as a hallmark of "the computer."
Technical details
- Density
- The earliest recording density was 100 characters per inch; subsequent versions increased this to 200, 556, and 800 characters per inch.
- Inter-record gap
- Originally set at one inch, this gap was later shortened to 3/4 inch to accommodate faster tape start and stop times.
- Latency
- The delay for a stationary tape to reach full read/write speed was minimal, approximately 1.5 milliseconds.
- Markers
- Aluminum strips placed near the ends of the tape served as logical indicators for the beginning and end of the tape.
- Write protection
- Write permission was controlled by a removable plastic ring attached to the back of the reel.
Generations
| IBM model | |||||
|---|---|---|---|---|---|
| 726 | 727 | 728 | 729 | 7330 | |
| Density (chars/in) | 100 | 200 | 248 | 200, 556, 800 | 200, 556 |
| Tape speed (in/s) | 75 | 75 | 75 | 75 (112.5) |
36 |
| Transfer rate (chars/s) | 7,500 | 15,000 | 18,750 | 15,000 41,700 60,000 (22,500 62,500 90,000) |
7,200 20,016 |
| End-of-record gap | 1 inch 100 chars 16.67 words |
0.75 inches 150 chars 25 words |
0.75 inches 186 chars 31 words |
0.75 inches 150,417,600 chars 25,69.5,100 words |
0.75 inches 150,417 chars |
| Rewind speed (in/s, avg.) | 75, read backwards | 500 | 500 | ||
| Start time (ms) | 10 | 5 | 5 | ||
| Stop time (ms) | 10 | 5 | 5 | ||
| Max. length of reel (ft) | 1,400 | 2,400 | 2,400 | 2,400 | 2,400 |
| Base composition | cellulose acetate | PET film or cellulose acetate | PET film or cellulose acetate | PET film | PET film |
IBM 726
The IBM 726 dual magnetic tape reader and recorder designed for the IBM 701 was unveiled on May 21, 1952.
IBM 727
Introduced on September 25, 1953 for both the IBM 701 and IBM 702, the IBM 727 Magnetic Tape Unit became IBM's primary tape drive throughout the vacuum tube computing era. Production ceased on May 12, 1971.
IBM 728
The IBM 728 magnetic tape drive operated on the SAGE AN/FSQ-7 computer and bore similarities to the IBM 727 but included unique features:
- Tracks: six data plus one synchronization track
- Words: six characters comprising thirty-two data bits, one parity bit, and three end-of-file bits
- Density: approximately forty-one point three-three words per inch
IBM 729
Serving as IBM's principal magnetic tape mass storage device from the late fifties into the mid-sixties, the IBM 729 Magnetic Tape Unit supported late models in the IBM 700/7000 series along with many systems in the IBM 1400 series. Its dual-gap head assembly allowed for immediate read-after-write verification.
IBM 7330
The IBM 7330 Magnetic Tape Unit represented an economical and slower tape storage solution that found extensive application alongside 1400 series computers.
IBM 2400 Series
Launched alongside the System/360, the 2400 Series Magnetic Tape Units predominantly utilized the IBM 9 Track format, though they were also available with seven-track heads to support reading and writing on seven-track tapes.
Legacy
By 2020, IBM still offered magnetic tape cartridge drives employing half-inch tape technology within the Linear Tape-Open and 3592 formats.