Storage Tube

Mostly obsolete, a storage tube is a special monochromatic CRT whose screen has a kind of 'memory' (hence the name): when a portion of the screen is illuminated by the CRT's electron gun, it stays lit until a screen erase command is given. Thus, screen update commands need only be sent once and this allows the use of a slower data connection, typically serial—a feature very well adapted to computer terminal use in 1960s and 1970s computing. The two main advantages were:

• Very low bandwidth needs compared to vector graphics displays, thus allowing much longer cable distances between computer and terminal
• No need for display-local RAM (as in modern terminals), which was prohibitively expensive at the time.

Generally speaking, storage tubes could be divided into two categories. In the more common category, they were only capable of storing "binary" images; any given point on the screen was either illuminated or dark. The Tektronix Direct-View Bistable Storage Tube was perhaps the most famous example in this category. Other storage tubes were able to store greyscale/halftoned images; the tradeoff was usually a much-reduced storage time.

Some pioneering storage tube displays were MIT Project MAC's ARDS (Advanced Remote Display Station), the Computek 400 Series Display terminals (a commercial derivative), which both used a Tektronix type 611 storage display unit, and Tektronix's 4014 terminal, the latter becoming a de facto computer terminal standard some time after its introduction (later being emulated by other systems due to this status).

The first generalized computer assisted instruction system, PLATO I, c. 1960 on ILLIAC I, used a storage tube as its computer graphics display. PLATO II and PLATO III also used storage tubes as displays.