David Empson wrote:
Bryan Parkoff <BParkoff@satx.rr.com> wrote:
<snip>
Think about the earliest resolution on IBM PC. IBM PC had only 160x100 resolution with two colors. It had 4x4 pixel font for 40/80 columns. Please correct me if I am wrong.I don't know the details of anything which predates CGA.
The earliest graphics display for the IBM was the CGA. The only thing that predated it was the monochrome display adapter, which didn't do graphics.
He might be thinking of the PCjr which had more colors and more resolution options, but didn't have a better resolution than the CGA.
CGA supports 4 colours (either of two sets) at 320x200, and two colours (white in combination with any of the sixteen colours) at 640x200. Don't forget that CGA was designed to be used with a digital RGB monitor, while the Apple II (which predates it by at least three years)
If my memory is accurate (and I wouldn't bet the farm on this) teh CGA came out early in 1982.
was designed to work with a television. Completely different beasts.Why did IBM PC only show 4 colors (black, white, blue, violent) on 320x200 resolution and another 4 colors (black, white, yellow, green) on another 320x200 resoltuion.Because the data representation of the image only had room for two bits per pixel in 320x200 mode (one bit per pixel in 640x200 mode).Apple II's high resolution allows to combine 8 colors together.Well, six colours, and don't forget that the effective colour resolution for hi-res graphics mode is only 140x192. If CGA supports a 160x200 mode, then it could have four bits per pixel and 16 colours anywhere on the screen.
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.
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.
Roy
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