they are shader pipelines, 48 parallel shader pipelines for the GPU. Also, its NOT HT technology. It is 3 cores. Think of it like cell technology built on a single die. Also fadingtheory, as stated there are upgrades available for the 360 via xpansion ports for memory and (SUPPOSEDLY) processor upgrades. As far as the pipelines, here is a article explaining it:
XBOX 360 REMAINS the centre of everyone's attention and we have some more juicy things to say about its graphics. We even have a diagram!
As most of you know by now, ATI developed the XBox chip and the it's codenamed R500. It took ATI two years to finalize this design and this chip is unlike any other graphics chip yet seen. It will be even more advanced than the soon-to-be-announced R520, aka "Fudo".
If we remember correctly, the R500 is an advanced version of a chip once codenamed R400 - the one that ATI was working on after R350, Radeon 9800PRO. You can see here that ATI cancelled it but I am sure that we wrote about it on the INQ before.
R400 was supposed to have unified Shaders and to be heavily programmable and thats exactly what the R500 is. It has three blocks each having 16 pipelines that can do pixels or vertices at the same time. This gives you a total number of forty eight pipelines that can process either pixels or vertices.
Each block of 16 pipelines has its own vertex cache to store some data while processing vertices and they all together communicate with 10MB of EDRAM memory connected with ultra fast bus of 256 GB/s. This memory allows ATI to have "Free" FSAA and it sounds like Xbox might end up with amazing graphics anti aliased at the same time.
ATI built this chip with 90 nanometre marchitecture but we dont yet know how many transistors you actually need to make such a chip.
Compared with desktop parts this chip will be more advanced than the R520 and it should be comparable with the R600 generation of cards - the one scheduled for autumn of 2006. This one will have WGF 2.0 compliance and will be able to deal with Shader model 4.0 at the same time.
So.. uh, yes it does.