DVBST

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DVBST was an acronym used by Tektronix to describe their line of "Direct-View Bistable Storage Tubes". These were cathode ray tubes (CRTs) that stored information written to them using an analog technique inherent in the CRT and based upon the secondary emission of electrons from the phosphor screen itself. (See the discussion of "Analogue Storage" in the oscilloscope article.) The resulting image was visible in the continuously glowing patterns on the face of the CRT.

DVBST technology was anticipated by Andrew Haeff of the (United States) Naval Research Laboratory, and by Williams and Kilburn in the late 1940s. Tek's Bob Anderson reduced to practice the science and technology in the late 1950s to yield a reliable and simple DVST.

Tektronix-made DVBSTs were used for analog oscilloscopes (first in the 564 oscilloscope, then the type601 monitor, the 611 monitor, the 7613 plug-in mainframe oscilloscope, all from Tektronix) and for computer terminals such as the archetypal Tek 4010 (the "mean green flashin' machine") and its several successors including the Tektronix 4014. Portions of the screen are individually written-to by a conventional electron beam gun, and "flooded" by a wide, low velocity electron gun. Erasure required erasing the entire screen in a bright flash of green light, leading to the nickname.

Some DVBST implementations also allowed the "write-through" of a small amount of dynamically refreshed, non-stored data. This allowed the display of cursors, graphic elements under construction, and the like on computer terminals.

[edit] Skiatron

Another version of a (non-Tekronix) DVBST was the "dark trace" CRT also known as the Skiatron. This CRT replaced the conventional light-emitting phosphor layer on the face of the tube screen with a scotophor such as Potassium Chloride (KCl). KCl has the property that when a crystal is struck by an electron beam, that spot would change from translucent white to a dark magenta color. By back lighting such a CRT with a white or green circular fluorescent lamp, the resulting image would appear as black information against a green background or as magenta information against a white background. A benefit, aside from the semi-permanent storage of the displayed image, is that the brightness of the resultant display is only limited by the illumination source and optics.

The image would be retained until erased by flooding the scotophor with a high-intensity infrared light or by electro-thermal heating. Using conventional deflection and raster formation circuity, a bi-level image could be created on the membrane and retained even when power was removed from the CRT. By using an arrayof dots, say 8 X 8, a larger pixel could be formed to represent 64 gray levels. One such device, the D38 Image Display, was made by DICOMED Corporation and a technical paper was presented at the 1972 Electro-Optical Conference in Geneva, Switzerland.