The ASR33 was a very popular model of teleprinter, .
Introduced about 1963 by Teletype Corporation and designed for light-duty office use, it was much flimsier (and less expensive) than its heavy duty cousin, the Model 35ASR, or earlier Teletype machines.
The printing mechanism was an array of levers, cranks, and a type cylinder on a movable carriage. The Model 33 printed up to 10 characters per second. Printing was limited to the upper case ASCII character set.
"ASR" stood for "automatic send and receive." The ASR 33 had a built in paper tape reader and tape punch and used 8 bit ASCII code including one parity bit). It could print and read or punch tape at the speed of 10 characters per second. The ASR33 tape reader was purely mechanical; 8 spring loaded fingers would be thrust into the tape, one character at a time, and an assortment of rods and levers would sense how high the finger rose, which told it whether there was a hole in the tape at that position.
The ASR32 was a similar device, but used five hole Baudot code and had a three row keyboard. The otherwise identical KSR33 and KSR32 models ("keyboard send and receive") lacked the paper tape reader and punch. RO33 and RO32 models ("receive only") had neither keyboard nor reader/punch.
The paper tape reader is on the lower left and the paper tape punch is directly above it. As it exits the machine, the tape passes under a triangular lip that allowed the tape to be easily cut by lifting against the sharp edge of the lip. The model 33 could accommodate an internal modem with an optional acoustic coupler to the right of the keyboard.
In the 1970s minicomputers frequently had a 20mA current loop interface for connection to a KSR or ASR teletype. As the price of electronic (rather than mechanical) terminals dropped this was gradually replaced by an RS-232 interface.
More expensive Teletype systems used photo readers that used light sensors to detect the presence or absence of punched holes in the tape. These could work at much higher speeds (hundreds of characters per second). More sophisticated punches were also available that could run at somewhat higher speeds; Teletype's BRPE punch could run at 60 characters per second.
Basic CRT-based computer terminals which could only print lines and scroll them are often called glass teletypes or dumb terminals to distinguish them from more sophisticated devices. Teletypes were gradually replaced in new installations by dot-matrix printers and CRT based terminals in the mid to late 1970s.