Re: Compare Atari and Apple II

[Sheldon Simms <sheldonsimms@yahoo.com>]

On Fri, 24 Oct 2003 03:54:35 +0000, Bryan Parkoff wrote:

>     Atari was competing against Apple II by adding 128 colors, but it does
> not have higher than 160x192 resolution.  Do you think that Apple Corp, Inc
> feels sorry that it can only limit up to 16 colors.  Do you think that 128
> colors are not important?  Why Apple IIgs can only display 16 colors out of
> 4096 colors instead of 256 colors out of 4096 colors?

Well actually the IIgs can display more than 16 colors at a time, but
to answer your question, using palettes larger than 16 colors would
require more bits per pixel. My old Mac II requires 8 bits per pixel
to index a 256-color palette.

Consider a hypothetical Apple IIgs that has a 320x240 display mode
where each pixel can display one of 256 independent colors. Such a
IIgs would require 320 * 240 = 76800 bytes of video memory -- but
this is larger than one 64k bank of memory. It would be impossible
to address the entire buffer without changing banks.

There are some conceivable hacks that would make this easier, but
Apple chose to deal with this memory problem by implementing 4-bit
pixels and allowing each line to have its own 16-color palette.
That way you get a lot of the benefits of having more colors while
using only 1/4 the space. That said, it is true that some pictures
are difficult to display well on the IIgs because of the limited
number of colors per line.

-Sheldon