I was reading about memory hierarchy and I read that you can built a computer with just cache but it wouldn't be cost effective. I was wonderig if super computers are made with only cache technology?
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Perhaps its a misunderstanding that supercomputers are primarily about speed, because that's not necessarily the case. Supercomputers are about computing, about power. Dealing with very large sets of data containing very large or very complex values very quickly. This doesn't require speed so much as power: super-wide buses, huge instruction sets, and the ability to send huge amounts of data around to various places pretty quickly. That last part is the only part where "speed" as we generally conceive of it really comes in and it's generally dealt with by using superfast networking, because most supercomputers are just too large for information to be shuttled between components by pathways etched in silicone. I suppose it may be easy to misunderstand this as well. Super computers are definitely fast. Faster than anything Alienware and $10k can get you. But most of their ability, the power, comes not from speed so much as that ability, previously stated, to do complex things with huge chunks of data all at once. | |||||||||||||
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no... supercomputers have regular memory, too. Example:
source: wikipedia Another example from Cray:
source: wikipedia | ||||
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By "cache technology" you are probably referring to the high-speed static RAM used for holding the memory data prefetched from main memory and/or not yet writtem out to main memory. You are probably not referring to the content-addressable memory used for holding the address tags. There was a time (post ferrite core but before the 1990s and the proliferation of PCs) when static RAM was used to populate the main memory of computers. As demand for memory capacity (total amount of memory installed) and density (memory per square inch of board area) increased, the paradigm of a simple memory subsystem using SRAM evolved into using dynamic RAM (that needed refresh circuitry) with cache to compensate for slower memory read/write cycles. The huge shift from SRAM to DRAM production has made a small price differential into a huge one, in addition to the power consumption and physical density disadvantages. A (super)computer could be built using SRAM rather than DRAM for main memory, but the cost-to-benefit ratio is low. SRAM only gets you raw memory speed, but DRAM augmented with modern cache technology can almost match that speed with less cost, volume and power consumption. Memory speed is only one parameter in overall computer performance. For supercomputers processing throughput is often improved by using parallelism, rather than the fastest technology money can buy. Parallelism by doubling the width of memory data bus. Parallelism by using multiple processors. One of the first demonstrations of an inexpensive massive parallel computer was based on 64(?) Intel i386 processors at CalTech. | ||||
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