Screen update speed of 8088 PC

Chuck Guzis cclist at
Wed Mar 15 17:37:57 CST 2006

On 3/15/2006 at 5:12 PM Jim Leonard wrote:

>To get around this, you write to CGA RAM while the beam is *not* 
>drawing, but retracing horizontally or vertically back to the next 
>scanline or display cycle.  You can transfer about 250 words during a 
>vertical retrace and exactly one word during horizontal retrace, so 
>that's 450 words per frame, so a snow-less full-screen update would take 
>3 frames (20fps).
>The obvious goal is to not be in the position of having to update the 
>*entire* screen.

Maybe cheating a little, but:

Alternatively, you can install an EGA card running in CGA compatibility
mode. You can even double-buffer the thing (write to one bank while
displaying the other).


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