Hi Jasen! :-)

 JB> still it takes at best two write cycles to write a 24 bit pixel
 JB> (an 8 bit write and a 16 bit write)  if the 16 bit write straddles a 
 JB> data-bus boundary it'll take 3 cycles, and these cycles happen at the 
 JB> video-bus speed not at the CPU speed.
Well, with write gathering and what not between the CPU and bus, it is hard
to say which writes occur in what ordering. If another write to the next
pixel comes next, those four writes might be combined into one (or two)
before sent over the bus.

On the other hand, one could also first read full 32 bits, modify 24 bits
and then write 32 bits back to the graphics card again.

 JB> with a 32 bit pixel it takes a single write and you're guaranteed to 
 JB> always fit inside the bus bouandary.
Likely, yes.

Another consideration is framebuffer size... 32 bits means 1 byte per pixel
is lost, which makes for smaller texture buffers and other things.

 JB> OTOH these days if you're pushing single pixels around using the CPU 
 JB> you're probably doing whatever graphics task the slow way.
That's for sure. :)

 JB> yeah I guess they could go for a 24 bit data bus on the video card,
 JB> or something like that...
Well, current stuff usually has 256 bit or more internal data bus width.

Ciao
Pascal

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