IBM Magnetic Tape Selectric Typewriter IV
IBM MT/ST - 1964
The IBM MT/ST (Magnetic Tape/Selectric Typewriter) also known as the MT72 in Europe, is an IBM Selectric typewriter built into a desk and a enclosure containing magnetic tape recording, playback, and editing circuitry. It was introduced in July 1964, and was discontinued in 1983. It was the first system to be marketed as a word processor. It recorded text typed on the Selectric typewriter onto 1/2" magnetic tape held in a small cartridge. Each 100 foot magnetic tape cartridge held about 24,000 characters, about 10 pages of double-spaced text. The MT/ST Model II had one magnetic tape drive, and the Model IV had two. Having two magnetic tape drives made revising documents easier and enabled mail merge. The MT/ST Model I and III were the same as the II and IV, but didn't have the search and adjust capability. The magnetic tape cartridge was originally developed in 1955 for an electronic typing calculator that IBM never made. An IBM 2495 Tape Cartridge Reader allowed EBCDIC encoded MT/ST tape cartridges from a modified MT/ST to be ready by an IBM 360 mainframe for further processing.
The MT/ST had automatic word wrap, but didn't have a concept of a document page. Pages had to be numbered by the operator during playback. The backspace key backed up the tape so a character on the tape could be replaced. There was also a true backspace code, which allowed overstruck characters, like the á character. Text insertion capabilities were very limited. You could copy text from one tape drive to the other, insert new text, and then continue copying the tape. A "switch code" instructed the playback to switch to the other tape drive. In a cumbersome way, points on the tape could be marked and jumped to.
In July 1971 the Communicating MT/ST was introduced. This version could act like an IBM 2741 Printing Computer Terminal and connect to an IBM System/360 mainframe computer.
The MT/ST is not electronic. It has 19 circuit boards for the magnetic tape drives, and all of the editing functions are implemented with electromechanical relays.
In 1967 IBM hired Jim Henson (of Muppets fame) to produce and direct a short film on the MT/ST called Paperwork Explosion.
The first novel to be written on a word processor was written on a MT/ST. Len Deighton's leased a MT/ST in 1970 to write the WW-II historical novel Bomber.
In 1969 IBM introduced the Magnetic Card Selectric Typewriter. The RICM has two of these in the collection.
The magnetic tape path in the MT/ST. The white solonoid lifts the magnetic tape against the tape head. The tape head moves side-to-side to record the bits from a Selectric key press onto the tape. The tape then goes over the drive sprocket, and down into the tape bin.
The front of the MT/ST. The black boxes are the magnet tape cartridges.
The fourth version of the MT/ST
Tape Control Panel
The back side of the control panel
It is surprising to see that some if the parts in the MT/ST are used, not new.
The Selectric Typewriter is incredibly complicated. The grease on the rotating components is old and dried out, so everything is seized up. It will be a big job to get everything working again.
The left side of the MT/ST. The large square box holds the magnetic tape from the tape cartridge.
A top view of the MT/ST. The tape cartridges are at the top and bottom left. The motor at the right drives the mechanism to the left and the cooling blower to the right. There are lots of microswitches and solonoids in the mechanism that will need cleaning and adjusting.
The magnetic tape looks like 16mm film coated with magnetic material.
There are 19 circuit boards at the top that contain resistors, capacitors, and transistors. The MT/ST was made before microprocessors were invented, so all of the logic is implemented with relays, 79 of them. The contacts in each of the relays will need to be cleaned.