COREs vs processors

Posted on 2011-10-12
Medium Priority
Last Modified: 2012-05-12
i am confused about cores and processors , each processor must have at least one core right?
Question by:NAMEWITHELD12
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jhyiesla earned 500 total points
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When you think of processors, think CPU, think the physical chip. Every processor has at least one core. Today, most, if not all, processors have at least two cores; which looks to the OS, typically,  like two processors.
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Callandor earned 500 total points
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Before multi-core processors were invented, a processor was a single core.  Someone thought to put the equivalent of two separate processors on a single chip, and that was how multi-core processors came about.  Hyperthreading is another kind of core - a logical processor, which is nothing more than using spare cycles of a core to do additional work.
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dbrunton earned 500 total points
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garycase earned 500 total points
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Careful of the symantics.

Conceptually it's very simple:

One core = one central processing unit (CPU).    In the past this was often referred to as the "processor".

But today the "processor" generally means the physical chip that contains the central processing unit(S) (emphasis on the S) ==> and can contain more than one processing unit (e.g. core).

A system with one quad-core processor has one physical processor with 4 processing units (cores) on that chip.    A system with four single-core processors would also have 4 processing units, but only one on each physical chip.

The operating system will see the correct number of cores, regardless of how they are physically located.

Just to add yet-another layer of complexity, hyperthreading will cause each core to "look" like two cores to the OS, but a hyperthreaded core only has one processing unit.    Instead of an extra core, hyperthreading adds a complete 2nd set of registers to the core and its arithmetic units, which allows virtually instantaneous context switching between the two register sets, so the actual processing elements can be shared between two threads.

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