The 640k "barrier" (was: Re: cctalk Digest, Vol 44, Issue 54)

Chuck Guzis cclist at
Sun Apr 22 10:59:14 CDT 2007

On 22 Apr 2007 at 8:23, Chris M wrote:

 My question is therefore is this practical
> or even feasible? My guess is it's possible, but some
> code could be so convoluted that it would be extremely
> difficult. In essence the software would need enough
> intelligence to reverse engineer another bunch of
> code.   Could it be done totally by automation...

I suppose it all depends if you're talking about text or graphics.  
Text is pretty simple, but graphics bit- and port-level compatibility 
is a different matter.   Still, it's possible to search an app for 
video display buffer segment loads and alter them.  Recall that many 
apps would work on both MDA/MGA and CGA and so altered which addess 
that was used on the fly.   Note that apps that used CGA 80x25 text 
may not work without more probing as a "stall" waiting for the 
retrace interval to avoid snow in the display was very commonly used 
and may well cause your application to hang without modification.

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