The Nintendo Gamecube interesting in comparison with the Xbox. The Gamecube is a machine designed for the same purpose as the Xbox — gaming — but with a very different design philosophy in mind. The Xbox and the Gamecube both use the same gross architecture — a CPU, a graphics coprocessor, some memory, and some support chips — but the similarities end there. The Gamecube design demonstrates an exacting attention to detail and cost. The Gamecube motherboard is small and simple, the component count is kept to a minimum, and the heat sinking and thermal design is very simple. The clean, straight layout of most of the PCB traces on the Gamecube motherboard reflects the fact that almost every IC is custom-designed specifically for the Gamecube. As a result, the Gamecube is a much more economical platform to build than the Xbox.
One can recognize the gross organization of the Gamecube by inferring each chip’s function from the basic marketing information Nintendo provides.
Further details about the architecture of the Gamecube are difficult to infer, because it uses so many custom components that have no counterpart in a standard PC. By the pattern of the traces on the motherboard, one would be lead to believe that the large chip in the center of the board, the
“Flipper” chip, is the equivalent of an integrated graphics Northbridge chip in a PC. This is almost correct. A key difference is that even though the Flipper chip combines both a memory controller and a graphics controller into a single package, the graphics function still has its own dedicated memory, built inside the same chip. This kind of organization allows a very high performance memory to be used by the graphics engine, with the trade-off of the memory being a bit smaller than if trade-off-chip memories were used.
The smaller size of the on-chip memory is compensated in part by the use of extremely fast off-chip memory.
The Gamecube does not use DDR SDRAM like the Xbox; instead, it uses what is called a 1-T SRAM. 1-T SRAMs are DRAM memories that emulate a very fast type of memory known as the Static RAM (SRAM).
SRAMs have much lower random access latencies than DRAMs, and they also do not require each memory cell to be refreshed 30 times a second like DRAM does. The actual magic behind how DRAM can masquerade as fast SRAM is fairly complicated and is beyond the scope of this book, but you can find more information at the 1-T SRAM manufacturer’s website,
www.mosys.com.
Figure 2-8: Gamecube motherboard plus its power regulator card. The motherboard is about half the size of the Xbox motherboard.
The Gamecube also has yet another piece of memory, known as ARAM, that is slower than the 1-T SRAM memory, and is used to store things like audio samples that do not require high-bandwidth accesses. Having a disparate memory architecture means that the Gamecube can squeeze a more consistent amount of performance out of each subsystem, some-thing important in keeping frame lag to a minimum. The trade-off, however, is that the Gamecube can be more difficult to program, and mismanagement of the multiple pieces of memory can lead to performance problems.
Another important distinction between the Gamecube and the Xbox is that the Gamecube consumes much less power than an Xbox. Power consumption may seem unimportant at first, since both consoles are designed to be plugged into a wall outlet, but the Gamecube’s lower power envelope requires fewer heat transfer components and smaller power supplies to be used, saving on cost. Figure 2-8 includes a picture of the Gamecube power regulator for reference; the power regulator is a fraction of the volume of the Xbox power supply plus the local switch-ing regulators on the Xbox motherboard.
To be fair, note that the Gamecube does have a small external AC to DC converter, while the Xbox takes wall power directly into the console.
Furthermore, electronic components degrade much faster at elevated temperatures, as described by the rule of Arrhenius. For example, a 10 degree Celsius operating temperature increase roughly doubles the failure rate of a component. As such, the Gamecube should be more reliable over the years than the Xbox since the Gamecube puts out less heat, and because its thermal management system is as good as, if not better, than the Xbox’s.
Finally, it is interesting to note that the Gamecube uses proprietary I/O interfaces everywhere. The game disk format is a mini-DVD format, and the DVD reader connects to the motherboard through a proprietary connector. Using a smaller DVD media allows Nintendo to reduce the latency of data seeks, which means shorter game loading times. The game controllers and memory cards also use a proprietary signaling format.
Everything in the Gamecube is somewhat similar to our familiar PC, but nothing was directly incorporated into the design unchanged.
In addition to optimizing the manufacturability and cost of the Gamecube, the use of mostly proprietary chips and standards makes the console much more difficult to reverse engineer than the Xbox. For example, note that in Figure 2-8, there is no obvious ROM chip in the Gamecube. Thus, in order to even start looking at Gamecube code, one has to hunt down and extract a ROM hidden somewhere in one of the chips on the motherboard! This is one of the rare times where security through obscurity works. Even if there were no security at all on the Gamecube, the cost and effort of trying to burn your own code onto Nintendo’s custom DVD format is just not worth it for the individual enthusiast.