Editing RAMDAC (section)

== Design ==
The size of each DAC of the RAMDAC is 6 to 10 [[bit]]s. The SRAM's word length must be at least three times as large as the size of each DAC.  The SRAM acts as a [[CLUT|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{{nbsp}}× [[24-bit color|24-bit]] SRAM which allows a selection of 256 out of {{val|16777216|fmt=commas}} (16.7 million) possible colors for the display.<ref name="FOLDOC" /> The contents of this SRAM can be altered when no pixel needs to be generated for transmission to the display, which occurs during the [[vertical blanking interval]] between every [[Video frame|frame]].

The SRAM can usually be bypassed and the DACs can be fed color directly by display data, for [[Color depth#True color (24-bit)|True color]] 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 only the DAC part without the SRAM is used.

A quick estimation on the pixel clock for a given output can be found with:<ref name="vesa"/>

: Pixels, horizontally, per line × lines, vertically, per display × 1.4 (factor in any blanking) × rate of display updates (refresh rate)

The ability to drive transitions for sharp edges usually incurs, for the RAMDAC, a significant requirement in excess of the pixel clock.

As of 2006, the DAC of a modern graphics card runs at a [[clock rate]] of 400{{nbsp}}[[MHz]]. However, [[video card]]s based on the [[XGI Technology|XGI]] Volari XP10 run at 420&nbsp;MHz DAC. The highest documented DAC frequency ever achieved on a production video card for the PC platform is 550&nbsp;MHz, set by BarcoMed 5MP2 Aura 76Hz by [[Barco (manufacturer)|Barco]].<ref name="barco"/>