At Hot Chips today, Microsoft's Xbox team unveiled details of the system-on-a-chip (SoC) that powers the newer, slimmer Xbox 360 250GB model. Produced on the IBM/GlobalFoundries 45nm process, it's fair to say that the new SoC (pictured above) is the first mass-market, desktop-class processor to combine a CPU, GPU, memory, and I/O logic onto a single piece of silicon. The goal of the consolidation was, of course, to lower the cost of making the console by reducing the number of different chips needed for the system, shrinking the motherboard, and reducing the number of expensive fans and heatsinks.
The SoC also makes the new Xbox design more power efficient, which is nice for consumers, but the real motivation behind boosting the console's efficiency is to reduce the size and cost of the power supply unit, and to realize the aforementioned savings on cooling apparatus.
Microsoft engineers presented the new SoC and apparently did a lot of the layout (or perhaps all of it) themselves. Given the unique requirement of consoles—the system must perform exactly like the original Xbox 360—and despite a five-year gap and multiple iterations of Moore's Law, the consolidation presented a few interesting challenges.
If you take a look at the block diagram, you'll notice that most of the blocks are fairly obvious: the triple-core CPU is there, as is the ATI-designed GPU, and then you have the dual-channel memory controller and I/O. But the purpose of the "FSB replacement block" may not be obvious. This particular block essentially implements a kind of on-die "frontside bus" with the exact same latency and bandwidth characteristics as the older bus that connected the CPU and GPU when they were discrete parts.
Full Story at Ars