The controversy over what will be included in Microsoft's second-generation Xbox console continued yesterday with the publication across the Net a purported internal Microsoft whitepaper describing the console's specifications.
Opinion is divided as to whether the document, said to come from the pen of Pete Isensee, Xbox Advanced Technology Group development lead, is genuine. But at least one site is claiming that software developers who have seen the white paper say it's very close to what Microsoft is telling development partners.
The document discusses the three-core IBM PowerPC processor clocked to 3.5GHz or more, memory complement of 256MB or more, and 500MHz graphics chip from ATI with 10MB of embedded SDRAM already detailed in an alleged schematic for the console that appeared on the Web last April.
Apparently, the CPU will feature anti-piracy and anti-hacking security technology on the die, along with 1MB of shared L2 cache - up from the schematic's claim that there would be 512KB of L2 - and 64KB of L1 cache per core split 50:50 for instructions and data. Each core is enabled for simultaneous multi-threading - the ability to convince the host OS it's two cores rather than one. In other words, the OS - derived, says the document, from Windows NT - sees six logical cores rather than three physical ones.
Each core is said to be able to issue two instructions per clock, which is fewer than the PowerPC 970/G5's five. The document also mentions "128 vector (VMX) registers", when the G5, for example, has a single register file containing space for 32 architected registers and 48 renameable registers 128-bit vector instructions.
The GPU is said to contain a shader core equipped with 48 arithmetic units "that can execute 64 simultaneous threads on groups of 64 vertices or pixels" - whether they work on vertices or pixels, depends on the workload, apparently.
"The GPU has a peak pixel fill rate of 4+ gigapixels/sec (16 gigasamples/sec with 4_ antialiasing). The peak vertex rate is 500+ million vertices/sec. The peak triangle rate is 500+ million triangles/sec. The interesting point about all of these values is that they're not just theoretical-they are attainable with nontrivial shaders," the doucment states.
Interestingly, it also mentions the GPU's ability to snoop the CPU's L2 cache, apparently a feature little-known outside the developer community until now. Indeed, developers working in Xbox 2 - aka 'Xenon' - code told GamesIndustry.biz that the document was close to what Microsoft has indicated to them separately.
"I've not actually seen this specific document coming from Microsoft," one developer said, "but there's certainly nothing in there which doesn't fit with what they've been telling us.
"If this is a hoax, which I doubt, it's a hoax so close to the truth that it hardly makes any odds."
The document doesn't address Xbox backward compatibility, but does not the difficultly in offering such a feature. However, it implies there's enough horsepower in the CPU to cope with the emulation overhead. ®