A Charactron was a specific type of cathode ray tube that contained a form of read-only memory.

There were two types of Charactrons:

1. Video scan: not meant for direct display, these instead generated data in the form of electrical pulses that could be combined with a video signal and then displayed on other devices (including other CRTs)
2. Direct view: contained dual sets of deflection plates, one to select the character and another to position it on the phosphor screen; these were used as computer and radar displays and as highspeed computer photo printer devices

Essentially, it used an electron beam to scan a specially-patterned anode that contained the dot patterns for each of the characters that it could form. The gross positioning of the electron beam selected among the many characters that could be formed and fine scanning of the electron beam was then used to read out the bit pattern of the selected character (in direct view Charactrons a wide electron beam was used that covered an entire character's matrix at the same time, no "fine scan" was needed). A 5x7 dot matrix was typical.

Because the electron beam was steered electrostatically, access time to the individual character data was very fast.

Patents

External links

• Photos of a Video scan Charactron EMI 9788 tube
• Description of a Direct view Charactron used on a UNIVAC 1107 computer in the late 1960s