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Re: High Resolution With 16 colors?
Dosius wrote:
Exegete <millers@noneofyourbusiness.com> wrote in message news:<3E64B79E.8000402@noneofyourbusiness.com>...
The PCjr could have more colors than the CGA because the PCjr had
something called VGA (Video Gate Array, without checking out Norton's
book) which stole the top 16K of RAM for the video. This gave the jr
more video RAM than the CGA, but it also is why Lotus 123 which could
run on a 128K PC, couldn't run on a 128K PCjr.
Er...
Actually, the PCjr didn't have the VGA - that came with high-end
models of the PS/2 in 1987. But you are correct on how the graphics
adapter worked. (I think though that there were other reasons why
1-2-3 wouldn't run on a PCjr.) The PCjr video functionality was never
named officially ;)
Er...
"The PCjr strays from the family tradition by using low address
locations in main memory for its display memory. However, special
circuitry in the PCjr closely mimics the conventional Color/Graphics
Adapter. This circuitry, called video gate array (VGA), makes it appear
as though the PCjr's display memory is located at the Color/Graphics
Adapter's B800 address. References to the B800 area are routed by the
VGA's circuitry to whatever location is actually in use as display
memory. The PCjr can use any part of the first 128K of RAM for video
memory; the VGA keeps track of the actual location. For all practical
purposes, the PCjr should be treated as a PC equipped with a
Color/Graphics Adapter, which uses the display memory address beginning
at B800."
The Peter Norton Programmer's Guide to the IBM PC
pg 69
copyright 1985.
I suggest you reread my post. I wasn't referring to the VGA that we all
know and "love", and Norton couldn't have since his book was copyrighted
two years before THAT VGA was released. He does, however, address the
EGA and PGA.
There was a version of 1-2-3 that DID run on the jr, but it was loaded
via cartridges, thus not taking up RAM for the program code.
Roy
What seems strange to me is that 3-4 years after the II was released,
IBM's first color graphics mode was barely better in resolution, and not
as good in color. I suppose because they thought businesses didn't need
color, and Woz was creating a computer that he could play games on.
I agree with that statement.
-uso.
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