On 26 Apr 2004, at 07:38, Byron Q. Desnoyers Winmill wrote:
On Mon, Apr 26, 2004 at 07:24:20AM +0100, Mark Benson wrote:The limiting factor as far as Macs go is that you need more VRAM space
to page the screens to if you run at higher refresh rates. Think about
the refresh rate as 'screens per second' and in a given time frame you
have to store more pixel information in the VRAM. Thus larger pages (as
Thousands of colours is) take up more space per second. Therefore at
one instance it can store less thousands pages than 256 colour ones.
WTF? The performance and the video and memory made some sense, but this does not. Video chips (at least on older systems) typically have one or two pages. The only reason for the second page is to hide redrawing the screen from the user, in order to avoid some nasty artifacts. The only time you are concerned with video timing, as a programmer, is to switch pages at the right time (else you get flicker). If you have a greater number of video pages, you are buffering data for some reason, and you don't create big buffers on low memory systems because it will hurt performance.
Byron.
I think the problem here is that Mark tried to simplify the issue in non-technical language, but that in doing so, appeared to be involving pages of VRAM, which aren't used, AFAIK, in early Macs.
Is a better analogy trying to get large groups of people along a road?
If there are 256 people in each group, you can get more _groups_ along the road in an hour than if there are thousands of people in each group, assuming that the people can only walk at the same speed.
In the case of video displays, one screen of data is analagous to the group of people, and the road is analagous to the data path ways along which the data travels from the VRAM to the display chips.
So, if you have 'big' groups -1000s of colours - fewer groups can get to the display chips than if the 'groups' are of 256 colours, in any given time. So with big groups, they arrive less frequently - i.e. the display refresh rate has to drop.
Confused?
Stuart
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