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which of the following memory has the shortest access time?

  1. Virtual memory
  2. Cache memory
  3. External memory
  4. Register

When I try to select the correct answer, I feel like it must be cache memory but answer is Register. Is it so? Please explain me more.

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Register memory is build into the CPU, so it is the closest to the point of access with the lowest amounts of latency.

How Computer Memory Works

The final step in memory is the registers. These are memory cells built right into the CPU that contain specific data needed by the CPU, particularly the arithmetic and logic unit (ALU). An integral part of the CPU itself, they are controlled directly by the compiler that sends information for the CPU to process. See How Microprocessors Work for details on registers.


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There is a fairly good summary/article of that from the same page as the image if from. Source

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Note that cache memory is almost always built in to the CPU these days, too. – ChrisInEdmonton Aug 22 '13 at 14:07
@ChrisInEdmonton - True, I guess I should distinguish that the registers are actually where the operations are happening - not necessarily in all of them as some are used as holders for counters, offsets, etc. So the cache is still a step further, but is more memory typically. – nerdwaller Aug 22 '13 at 14:59

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