IBM 727
{{Short description|Early computer magnetic tape drive, 1953}}
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 The 727 was withdrawn on May 12, 1971.{{Cite web|url=https://www-03.ibm.com/ibm/history/exhibits/701/701_1415bx27.html|title=IBM 727 Magnetic tape unit|last=|first=|date=|website=|publisher=IBM|archive-url=https://web.archive.org/web/20050122222837/http://www-03.ibm.com/ibm/history/exhibits/701/701_1415bx27.html|url-status=dead|archive-date=January 22, 2005|access-date=}}
Overview
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. Reflective strips were glued several feet from the ends of the tape to serve as physical beginning and end of tape markers. Write protection is provided by a removable plastic ring in the back of the tape reel. Installing the ring enables writing, thus strictly speaking, it is a write enable ring, and removing it protects the tape from being written to.
| class="wikitable" |
| 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 |
Gallery
Image:IBM_704_mainframe.gif|An IBM 704 mainframe with IBM 727 tape drives on the left. (image courtesy of LLNL)
File:Write protect ring.agr.jpg|Half-inch tape reel with write enable rings
File:Model of IBM 727 Tape Drive (7100678957).jpg|Model of an IBM 7272 tape drive