How The 360 Works

The always informative How Stuff Works site has an article today entitled How the Xbox 360 Works. From the piece: "The other interesting thing to note about the Xbox 360 CPU is that each core is capable of processing two threads simultaneously. Think of a thread as a set of instructions for a program's job. The core processes these instructions and does the heavy lifting to get the job done. A conventional processor is traditionally capable of running a single execution thread. Because the Xbox 360 cores can each handle two threads at a time, the 360 CPU is the equivalent of having six conventional processors in one machine."

Comments

Re:More like 3.90 processors

[iota]

> Because the two threads in the chips share arithmetic and floating point units and whatnot,
> they get best case throughput of 1.3x a single threaded chip. This is according to Sony who has the same PPU on their PS3.

I don't mean to be too pedantic here, but you are not correct.

The Cell PPU unit and the XBOX360 PPC unit are not the same. They are related by the fact that they are both PPC designs, but that is as far as it goes. The XBOX360 PPC has two fixed-point, two floating-point and two VMX units per core - thread switching is done on fetch stalls. The Cell PPU has two register files but only single fixed-point, floating-point and VMX units - threading is accomplished by switching between the register files. The branch prediction units are also different, and the caches, and the memory mapping. As a matter of fact, the only thing the two processors share is an instruction set and an IBM invoice.

The number you (mis-)quote originally came from a lecture in an SCEA conference. You apparently don't understand the context under which it was said, and thus why it makes no sense to discuss here - nor do you appear to understand the NDA which, if you heard this directly from SCEA, are under. Although much of the Cell design and tools are public knowledge, it is necessary to keep confidential that non-public information which you have access to if you wish to continue to have access to it.