QuadraScan

A vector monitor or vector display is a display device used for computer graphics up through the 1970s. It is a type of CRT, similar to that of an early oscilloscope. In a vector display, the image is composed of drawn lines rather than a grid of glowing pixels as in raster graphics. The electron beam follows an arbitrary path tracing the connected sloped lines, rather than following the same horizontal raster path for all images. The beam skips over dark areas of the image without visiting their points.

Some refresh vector displays use a normal phosphor that fades rapidly and needs constant refreshing 30-40 times per second to show a stable image. These displays such as the Imlac PDS-1 require some local refresh memory to hold the vector endpoint data. Other storage tube displays such as the popular Tektronix 4010 use a special phosphor that continues glowing for many minutes. Storage displays do not require any local memory. In the 1970s, both types of vector displays were much more affordable than bitmap raster graphics displays when a megapixel computer memory was still very expensive. Today, raster displays have replaced nearly all uses of vector displays.

Vector displays do not suffer from the display artifacts of aliasing and pixelation (especially, B&W ones; color displays keep some artifacts, due their discrete nature). But they are limited in that they can display only a shape's outline (advanced vector systems can provide a limited amount of shading). Text is crudely drawn from short strokes. Refresh vector displays are limited in how many lines or how much text can be shown without refresh flicker. Irregular beam motion is slower than steady beam motion of raster displays. Beam deflections are typically driven by magnetic coils, and those coils fight against rapid changes to their current.

Notable among vector displays are Tektronix large-screen computer terminals that use direct-view storage CRTs. Storage means that the display, once written, will persist for several minutes. (The CRT has at least one flood gun, and a special type of display screen, more complicated in principle than a simple phosphor.) But that permanent image cannot be easily changed. Like an Etch-a-Sketch, any deletion or movement requires erasing the entire screen with a bright green flash, and then slowly redrawing the entire image. Animation with this type of monitor is not practical.

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