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Specs Textures 1T-SRAM Motherboard |
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| One of the most interesting
things about the GameCube is design is memory bandwidth |
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GameCube Playstation 2 Xbox Dreamcast Glossary |
efficiency. It attains this efficiency
through the use of 1T-SRAM (1 Transistor Static RAM). It offers
lower latency operation and higher overall bus utilisation than conventional
DRAM. Before you understand exactly what that is, you have to look
at differences between DRAM and SRAM. The cache on the die on a CPU is a type of RAM known as Static RAM, or SRAM. The prefix "Static" comes from the fact that unline DRAM (Dynamic Random Access Memory), SRAM cells do not have to be constantly "refreshed" in order to retain their data (Since DRAM is capacitance based, it loses its charge after a while requiring a |
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| refresh of that charge in order to retain its data).
One of the reasons DRAM is so much slower is because of this constant
refreshing process. It turns out that when reading the contents of
a DRAM cell, the cell is actually refreshed making the most common way
of refreshing DRAM cells to actually read the contents of the cell. This is perfectly fine except for when the contents of the cells are being refreshed are being read from or written to. SRAM doesn't have this problem since it uses transistors to statically hold the data being stored in the memory. DRAM on the other hand uses a transistor and a capacitor to hold the data. The capacitor greatly reduces the size of DRAM cells thus making them cheaper to manufacture but also produces a problem of refreshing. The performance aspects of 1T-SRAM are very difficult to quantify because it has never been on a benchmarkable platform making the assessment of its value very difficult, however, Nintendo has saw it fit to make use of MoSys's 1T-SRAM in the GameCube design. The GameCube features 3MB of 1T-SRAM inside the flipper chip, and 24MB used as main memory. This 64-bit memory bus runs at twice the operating clock of the GPU, or 324MHz resulting in 2.6GB/sec on bandwidth between the flipper and the main memory. While this is only as much memory bandwidth as the original GeForce 256, remember that all of the Z-Buffer's acesses are done on the embedded 1T-SRAM and the frame being drawn is done initionally to the one-die buffer, this reduces the need for as much main memory bandwidth. There are significantly faster DDR-RAM devices available. 1T-SRAM is not as fast as the 233MHz DDR RAM in the Xbox, that would provide much more memory bandwidth. The only benefit the Cube gains from using 1T-SRAM as it's main memory is low latency access and thus better bus utilisation, coupled with the fact that the memory bus is is synchronised to the Gekko's FSB and Flipper operating frequency (162MHz x 2) we can assume that latency is reduced as much as possible with this design. Again, we see that the efficiency of the GameCube rather than raw power. |
