The meaning of "core"

[mainty]

Hello everyone,

Can anyone tell me the exact meaning of "core" ? Does it mean processor?

If so, does "multi-core" mean "multi-processor"?

I'm really confused with those terms...

[TimP]

Unfortunately, some of the terminology which has grown up isn't ideal. A core has come to mean a reasonably complete CPU subdivision of a chip, and has come to be the most satisfactory way to support Chip Multi Processing. We have also seen HyperThreading and Switch On Event Multi-Threading where there is partial hardware support for CMP. The individual cores can operate with reasonable independcnce, except that they compete for memory access. HT and SOEMT have far more restricted independence, but, if they have any value, also must be run as separate processors.
Multi-processor, when referring to Intel hardware, means multiple chips (sockets) on a motherboard. In a more general sense, it means either multi-core or multi-socket, or a combination, or even a cluster of motherboards. From the software point of view, you want to go as far as possible to make the software adaptable to a variety of hardware topologies, avoiding distinction between varieties of multi-processing.
What does wikipedia say?

[mainty]

Thanks Tim.

Wikipedia saysthat " ...dual-core closely resembled two interconnected Pentium M branded CPUs packaged, as a single die (piece) silicon chip (IC). ..."

(see http://en.wikipedia.org/wiki/Intel_Core)

So, as far as I understand, "multi-core" then can be seen as two or more processors wrapped in a single unit or box.

Am I right?

[robert-reed]

That Wikipedia notation is a little skewed. A core is the collection of essentials that form a physical processing element: the instruction pipeline andALUs, and thebuffers and caches that tie it all together, as opposed to what's sometimes called the un-core, the communications, outer caches and off-chip drivers that often surround the core. The processor Intel code-named Merom is such a beast: two cores that share an on-chip outer cache.

Extra cores can be obtained through tight integration as described above, or through replication. The Intel Core 2 Quad processor formerly known as Kentsfield uses essentially two Merom cores, sitting side by side.

However the cores are produced, the distinction of a multi-core processor to a single-core processor is the presence of more than one of these cores on a single chip, or part or socket. Multiple sockets can compound the number of cores on a board, which would go into whatsome people might refer to as a unit or box. It's all part of a hierarchy of multi-processing thatnow being extendedontoa singlechip has been stretched out one more layer.