What is a wait state?

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easyee - Jul 26, 2010 at 08:25 PM
xpcman Posts 19530 Registration date Wednesday October 8, 2008 Status Contributor Last seen June 15, 2019 - Jul 26, 2010 at 11:46 PM
Hello,
what is a wait state?

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xpcman Posts 19530 Registration date Wednesday October 8, 2008 Status Contributor Last seen June 15, 2019 1,825
Jul 26, 2010 at 11:46 PM
Nest time Google this yourself!

A wait state is a delay experienced by a computer processor when accessing external memory or another device that is slow to respond.

As of late 2007, computer microprocessors run at very high speeds, while memory technology does not seem to be able to catch up: typical PC processors like the Intel Core 2 and the AMD Athlon 64 X2 run with a clock of several GHz, while the main memory clock generally ranges from 667 to 1333 MHz. Some second-level CPU caches run slower than the processor core.

When the processor needs to access external memory, it starts placing the address of the requested information on the address bus. It then must wait for the answer, that may come back tens if not hundreds of cycles later. Each of the cycles spent waiting is called a wait state.

Wait states are a pure waste for a processor's performance. Modern designs try to eliminate or hide them using a variety of techniques: CPU caches, instruction pipelines, instruction prefetch, branch prediction, simultaneous multithreading and others. No
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