whats the difference between the ati radeon 9800 pro, XT and the SE?

Question

whats the difference between the ati radeon 9800 pro, XT and the SE

Answer 1

for ATI, SE stands for Standard Edition and is the entry level card in each serie; their memory bandwidth (thus the communication path between the memory chips on the graphic card and the GPU is usually limited to 64 or at most 128 bit.

Pro stands for the better configuration (usually the maximum memory bandwidth for the card type) and a somewhat faster GPU

XT is the ultimate gamer edition, with the maximum memory bandwidth and a faster GPU
see http://www.dvhardware.net/article2546.html for an illustration (for the X-800 serie, but the principle is the same for all ATI Radeon cards except that recently the SE is not always provided, especially for high-end cards.

those are the consumer cards, usually called Radeon.
based on the same circuit design and GPU, ATI also has a professional card line called FireGL which makes better use of the capabilities of the GPU.
for the X-800 series, this is the FireGL-X3 card. if a X-800XT sold for about 500 bucks a year or two ago (see link, 3 yrs old), the FireGL-X3 STILL sells for about 1'000 bucks (!)

Answer 2

For the 9800's, (i.e. R350 core), Pro is the fastest. XT is the "non-pro". SE is like a crippled non-pro, with half of the pixel processing units disabled, and often with half-sized memory bus.