Random Access Memory Digital-to-Analog Converter is a combination of three fast DACs with a small SRAM used in graphics display adapters to store the color palette and to generate the analog signals (usually a voltage amplitude) to drive a colour monitor. The logical colour number from the display memory is fed into the address inputs of the SRAM to select a palette entry to appear on the output of the SRAM. This entry is composed of three separate values corresponding to the three components (red, green, and blue) of the desired physical colour. Each component value is fed to a separate DAC, whose analog output goes to the monitor, and ultimately to one of its three electron guns (or equivalent in non-CRT displays). In electronics, a digital-to-analog converter (DAC or D-to-A) is a device for converting a digital (usually binary) code to an analog signal (current, voltage or charges). ... A six-transistor CMOS SRAM cell. ... A GeForce 4 4200-based graphics card A graphics card or video card is a component of a computer which is designed to convert a logical representation of an image stored in memory to a signal that can be used as input for a display medium, most often a monitor... A palette, in computer graphics, is a designated subset of the total range of colours supported by a computer graphics system. ... A computer display A computer display (also known as a computer monitor, computer screen, or computer video display) is a device that can display signals generated by a computer as images on a screen. ... Electron gun from a cathode ray tube An electron gun is a component that produces an electron stream that has a precise kinetic energy, being used in all TVs and monitors which use cathode ray tube technology, and in other instruments, eg. ... Cathode ray tube employing electromagnetic focus and deflection Cutaway rendering of a color CRT Electron guns Electron beams Focusing coils Deflection coils Anode connection Mask for separating beams for red, green, and blue part of displayed image Phosphor layer with red, green, and blue zones Close-up of the phosphor...

DAC word lengths range usually from 6 to 10 bits. The SRAM's word length is three times the DAC's word length. The SRAM acts as a color lookup table (CLUT). It usually has 256 entries (and thus an 8-bit address). If the DAC's word length is also 8 bits, we have a 256 x 24-bit SRAM which allows a selection of 256 out of 16777216 possible colours for the display. The contents of the SRAM can be changed while the display is not active (during display blanking times). BIT is an acronym for: Bangalore Institute of Technology Bilateral Investment Treaty Bhilai Institute of Technology - Durg Birla Institute of Technology - Mesra Battles in Time (Doctor Who magazine) Category: ... A Colour Look-Up Table (CLUT) is a device which converts the logical colour numbers stored in each pixel of video memory into physical colours, normally represented as RGB triplets, that can be displayed on a computer monitor. ...

The SRAM can usually be bypassed and the DACs can be fed directly by display data, for Truecolor modes. In fact this has become very much the normal mode of operation of a RAMDAC since the mid-1990s, so the programmable palette is mostly retained only as a legacy feature to ensure compatibility with old software. In many newer graphics cards, the RAMDAC can be clocked much faster in true color modes, when the SRAM is not used. Truecolor (also spelled Truecolour; called Millions on a Macintosh) graphics is a method of storing image information in a computers memory such that each pixel is represented by three or more bytes. ...

History

The term "RAMDAC" did not enter into common PC-terminology until IBM introduced the IBM VGA display adapter in 1987. The IBM VGA adapter used the INMOS G171 RAMDAC. The INMOS VGA RAMDAC was a separate chip, featured a 256-color (8-bit CLUT) display from a palette of 262,144 possible values, and supported pixel-rates up to ~30MPixel/sec. now. ... Video Graphics Array (VGA) is an analog computer display standard first marketed in 1987 by IBM. While it has been obsolete for some time, it was the last graphical standard that the majority of manufacturers decided to follow, making it the lowest common denominator that all PC graphics hardware supports... The INMOS Transputer was a pioneering parallel computing microprocessor design of the 1980s from INMOS, a small English company. ...

As clone manufacturers copied IBM VGA hardware, they also copied the INMOS VGA RAMDAC. Advances in semiconductor manufacturing and PC processing-power allowed RAMDACs to add "direct-color" operation, which is a mode of operation that allows the SVGA-controller to pass a pixel's color-value directly to the DAC-inputs, thereby bypassing the RAM lookup-table. Another innovation was Edsun's CEGDAC, which featured hardware-assisted anti-aliasing for line/vector draw-operations. Super Video Graphics Array, almost always abbreviated to Super VGA or just SVGA is a broad term that covers a wide range of computer display standards. ...

By the early 1990s, the PC chip-industry had advanced to the point where RAMDACs were integrated into the SVGA display controller chip, thus reducing the number of discrete chips and the cost of SVGA video cards. Consequently, the market for standalone VGA RAMDACs disappeared. Today, RAMDACs are still manufactured and sold for niche applications, but in obviously limited quantity.

In modern PCs, the VGA RAMDAC(s) are integrated into the display controller chip, which itself may be mounted on an add-in-board or integrated into the motherboard core-logic chipset. The original purpose of the RAMDAC, to provide a CLUT-based display-mode, is rarely used, having been supplanted by true-color display-modes. As LCD and other digital flat panel technology becomes increasingly mainstream, the "RAM" portion of the RAMDAC will likely become obsolete. A Colour Look-Up Table (CLUT) is a device which converts the logical colour numbers stored in each pixel of video memory into physical colours, normally represented as RGB triplets, that can be displayed on a computer monitor. ... Reflective twisted nematic liquid crystal display. ...

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL. The Free On-line Dictionary of Computing (FOLDOC) is an on-line, searchable encyclopedic dictionary of computing subjects. ... GNU logo (similar in appearance to a gnu) The GNU Free Documentation License (GNU FDL or simply GFDL) is a copyleft license for free content, designed by the Free Software Foundation (FSF) for the GNU project. ...