The first computer display devices were modified typewriters and Teletype machines. These devices were slow, noisy, and expensive, and could only handle text. For graphic output, an X-Y plotter, a device that pulled a pen over a piece of paper, was used. It shared all the problems of the Teletype machine.

It did not take long before these mechanical machines were replaced with electronic counterparts. The replacement was called a terminal. It consisted of a typewriter-like keyboard, which activated switches, and a display screen, which was a modified television receiver. Thus, the first computer display device was a cathode ray tube or CRT.

Cathode Ray Tubes

A cathode ray tube paints an image on a phosphor screen using a beam of electrons. The concept of the CRT was formulated before the nature of the electron was known. Cathode rays are not rays at all...