Teletype

Teletype is the name for the mechanical printing terminals for connection to an asynchronous serial line produced by the Teletype Corporation.

Many different models were produced over the years, but the one most commonly used with computers was the Model 33 - initially produced in the mid-60's, it used the ASCII code (uppercase only), operated at 10 characters per second, and used a cylindrical typewheel to print.

The Model 33 came in three different varieties:

• ASR (Automatic Send/Receive) - in addition to the keyboards and printer, it included a paper tape reader/punch on the side
• KSR (Keyboard Send/Receive) - as above, but no paper tape reader/punch
• RO (Receive Only) - only the printer

The ASR-33 (formally the "Model 33 ASR") was widely used on early minicomputers, as the paper tape option could be used to load binary program tapes. Although an EIA interface option was available, most used the 20mA current loop interface.

The later Model 38 added lower case, a number of special symbols, and a two-colour (red/black) printing ribbon.