Difference between core and processor [closed]

An image may say more than a thousand words:

* Figure describing the complexity of a modern multi-processor, multi-core system.

Source: Intel Performance Counter Monitor: A better way to measure CPU utilization

Let's clarify first what is a CPU and what is a core, a central processing unit CPU, can have multiple core units, those cores are a processor by itself, capable of execute a program but it is self contained on the same chip.

In the past one CPU was distributed among quite a few chips, but as Moore's Law progressed they made to have a complete CPU inside one chip (die), since the 90's the manufacturer's started to fit more cores in the same die, so that's the concept of Multi-core.

In these days is possible to have hundreds of cores on the same CPU (chip or die) GPUs, Intel Xeon. Other technique developed in the 90's was simultaneous multi-threading, basically they found that was possible to have another thread in the same single core CPU, since most of the resources were duplicated already like ALU, multiple registers.

So basically a CPU can have multiple cores each of them capable to run one thread or more at the same time, we may expect to have more cores in the future, but with more difficulty to be able to program efficiently.

CPU is a central processing unit. Since 2002 we have only single core processor i.e. we will only perform a single task or a program at a time.

For having multiple programs run at a time we have to use the multiple processor for executing multi processes at a time so we required another motherboard for that and that is very expensive.

So, Intel introduced the concept of hyper threading i.e. it will convert the single CPU into two virtual CPUs i.e we have two cores for our task. Now the CPU is single, but it is only pretending (masqueraded) that it has a dual CPU and performs multiple tasks. But having real multiple cores will be better than that so people develop making multi-core processor i.e. multiple processors on a single box i.e. grabbing a multiple CPU on single big CPU. I.e. multiple cores.

In the early days, like before the 1990s, the processors weren't able to do multiple tasks that efficiently, because a single processor could handle just a single task, so when we used to say that my antivirus software, Microsoft Word, VLC media player, etc. software are all running at the same time. That isn't actually true.

When I said a processor could handle a single process at a time, I meant it. It actually would process a single task. Then it used to pause that task, take another task, complete it if it’s a short one, again pause it and add it to the queue, and then the next.

But this 'pause' that I mentioned was so small (approximately 1 ns) that you didn't understand that the task has been paused. For example, on VLC media player, while listening to music, there are other applications running simultaneously, but as I told you, one program at a time, so the VLC media player application is actually pausing in between for nanoseconds, so you don’t understand it, but the music is actually stopping in between.

But this was about the old processors...

Nowadays, processors, i.e., third-generation PCs have multi-core processors. Now the 'cores' can be compared to a first-generation or second-generation processors itself, embedded onto a single chip, a single processor.

So now we understood what cores are, i.e., they are mini processors which combine to become a processor. And each core can handle a single process at a time or multi threads as designed for the OS. And they follow the same steps as I mentioned above about the single processor.

E.g., a Core i7 sixth generation processor has eight cores, i.e., eight mini processors in one Core i7, i.e., its speed is eight times the old processors. And this is how multitasking can be done.

There could be hundreds of cores in a single processor. E.g., Intel i128.

I found this link to be a clear explanation for me about the difference between a CPU (processor) and a core. So I'm leaving here some notes from there:

The main difference between a CPU and a core is that the CPU is an electronic circuit inside the computer that carries out instructions to perform arithmetic, logical, control and input/output operations while the core is an execution unit inside the CPU that receives and executes instructions.

Intel's picture is helpful, as shown by JohnTortugo's answer. Here's a caption for it.

Processor: One semiconductor chip, the CPU (central processing unit) seated in one socket, circa 1950s-2010s. Over time, more functions have been packed onto the CPU chip. Prior to the 1950s releases of single-chip processors, one processor might have spread across multiple chips. In the mid 2010s the system-on-a-chip chips made it slightly more sketchy to equate one processor to one chip, though that's generally what people mean by processor, as in "this computer has an i7 processor" or "this computer system has four processors."

Core: One block of a CPU, executing one instruction at a time. (You'll see people say one instruction per clock cycle, but some CPUs use multiple clock cycles for some instructions.)