资料来源 : Free On-Line Dictionary of Computing

Random Access Memory Digital-to-Analog Converter
     
         (RAMDAC) A combination of three fast {DAC}s with a
        small {SRAM} used in graphics {display adapters} to store the
        {colour palette} and to generate the analog signals 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).
     
        DAC word lengths range usually from 6 to 10 bits.  The SRAM's
        wordlength is three times the DAC's word length.  The SRAM
        acts as a {colour lookup table}.  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).  The SRAM can
        usually be bypassed and the DACs can be fed directly by
        display data (for {true colour} modes).
     
        (1996-03-24)