Stupid eBay user du jor

Chuck Guzis cclist at
Sun Feb 26 17:02:33 CST 2006

> I wonder how fast I can refresh an 80x24 VT display over a 19200 Baud
>RS232 link...

Well, depending on the "dumbness" of the program doing the refreshing it
can vary pretty wildly.  When I was doing the software for the "plug this
card into your PC in place of the normal MDA and drive your VT-100 (or 220)
with it, it was actually pretty surprising how well a VT220 at 19200 could
keep up with a monochrome 80x25 display.  All it took was a sufficient
amount of processing horsepower at the adapter end to make determinations
of what was going on and issuing the proper ANSI escape sequences.  We had
a threshold that once exceeded determined that it was faster to clear the
display and repaint it than send out all of the "move to (X,Y), clear to
end of line, etc." sequences.  Out of curiosity, I kept a counter that
recorded how many times in a session that actually occured.  It wasn't very
often--and typically coincided with an application clearing the screen.

Detecting scrolling activity was a bit tricky.  You couldn't hook the BIOS
routine to do it, because very few full-screen programs (like Lotus 1-2-3)
actually used the BIOS routines and in between samples, the screen may have
scrolled several lines.

I've sometimes wondered if much of Windows couldn't have been simplified
with a dedicated processor to track the contents of the various windowed
information instead of having the application redraw it all of the time.


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