James,
For an explanation about the differences between the various Radeon 9000 and 9000 Pro, I suggest you to read this comparative
article at X-bit Laboratories. They compare the performances of the Radeon 9000 varaint to the Radeon 8500 and a GeFarce 3Ti200.
About the Radeon 8500 and 9100 :
On Feb. 19th said:
The Radeon 9100 is a renamed 8500
And in this old
article, again at X-bit, it is written that :
Taking into consideration that currently RADEON 8500 LE cards have appeared in the market (they differ from ATI RADEON 8500 by lower price and lower frequencies, working at 250MHz/250MHz vs. 275MHz/275MHz of the regular RADEON 8500), we decided underclock our RADEON 8500 and to test it at the working frequencies of RADEON 8500 LE, i.e. at 250MHz/250MHz.
The new Sapphire Atlantis Radeon 9100 uses the same chip as the older Radeon 8500 (R200), but (upon
verification) at slightly lower frequencies.
To sum it up :
Radeon 7500 and lower : Radeon 256 core with thinner manufacturing process compared to the original Radeon DDR. Significantly slower than RV250 and above.
DirectX 7 support.
Radeon 9000 64MB & 128MB :
RV250, 250MHz core, 200MHz DDR RAM
Radeon 9000 Pro 64MB & 128MB :
RV250, 275MHz core, 275MHz DDR RAM
Radeon 8500LE 64MB & 128MB : R200, 250MHz core, 250MHz DDR RAM
Radeon 8500 128MB retail : R200, 275MHz core, 275MHz DDR RAM
Radeon 9100 64MB : R200, 250MHz core, 230MHz DDR RAM
Radeon 9100 128MB : R200, 250MHz core, 200MHz DDR RAM
RV250 and R200 chip support DirectX 8.1
Radeon 9500 and above : R300 core, much more advanced chipset.
DirectX 9 support.
I also found
this that could help you figure out the differences of the slower Radeon cards.