Direct-view bistable storage tube (DVBST) was an acronym used by Tektronix to describe their line of storage tubes. These were cathode ray tubes (CRT) 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. 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 US Naval Research Laboratory, and by Williams and Kilburn in the late 1940s. Tek's (Tektronix) Robert H. Anderson refined Haeff's concepts in the late 1950s to produce a reliable and simple DVST. Principle The DVBST implements two electron guns: a "flood gun" and a "writing gun". The writing gun scans across a wire grid, charging the grid to create the negative image. The flood gun then floods the grid. Previously charged areas repel the incoming electrons so that electrons only pass through the grid to the phosphor in those areas not previously charged. The technology offered several advantages and disadvantages. Advantages No refreshing is needed. Very complex pictures can be displayed at very high resolution without flicker. The cost is much lower. Disadvantages They ordinarily do not display color. Selected part of the picture can not be erased. The erasing and redrawing process can take several seconds for complex pictures. No animation in DVST. Modifying any part of image requires redrawing of entire image. Applications Tektronix-made DVBSTs were used for analog oscilloscopes (first in the 564 oscilloscope, then the type 601 monitor (1968), the 611 monitor, the 7313 and 7514 plug-in mainframe oscilloscope, all from Tektronix) and for computer terminals such as the archetypal Tek 4010 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 "the mean green flashin' machine". 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. Skiatron An alternate solution for storage tubes 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