Shared Memory Architecture
- memory capacity: there is a limit to the size of the whiteboard that you can fit into an office, i.e. there is a limit to the amount of memory you can put into a single shared-memory computer;
LimitationsIt turns out that memory access speed is a real issue in shared-memory machines. If you look at the processor diagram above, you’ll see that all the CPU-cores share the same bus: the connection between the bus and the memory eventually becomes a bottleneck and there is simply no point in adding additional CPU-cores. Coupled with the fact that the kinds of programs we run on supercomputers tend to read and write large quantities of data, it is often memory access speed that is the limiting factor controlling how fast we can do a calculation, not the floating-point performance of the CPU-cores.There are various tricks to overcoming these two issues, but the overcrowded office clearly illustrates the fundamental challenges of this approach if we require many hundreds of thousands of CPU-cores.Despite its limitations, shared memory architectures are universal in modern processors. What do you think the advantages are?Think of owning one quad-core laptop compared to two dual-core laptops – which is more useful to you and why?Share and discuss your ideas with your fellow learners!
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