|Teletype writer T 100 (Siemens) (ca. 1960)|
The teletype writer T 100 is basically an electronic typewriter, with a keyboard to type in text and with print hammers to write the received text onto paper. A paper tape puncher and a paper tape reader are integrated to prepare text for sending. The text is punched in 5-bit-code, i.e. 32 different characters can be coded. A shift key is used to switch between two groups of characters, letters on one hand and digits and symbols on the other hand. The 5-bit-code is used twice, so that more than 32 different characters can be transmitted. As opposed to the Hellschreiber, the transmission is more sensitive to noise, since a distorted bit changes the transmitted character completely at the receiver.
For transmission, a start bit and a stop bit are added to the 5-bit-characters, which are then sent
at 50 bits per second. This results in a maximum transmission speed of 400 characters per minute.
Teletype writers were widely used up to the nineties and are now replaced by the internet and electronic mail.
|The Teletype writer T 100 in action|