core and thread

a core is the cpu ie single core dual core whereas a thread is a windows technology see

http://msdn.microsoft.com/en-us/library/windows/desktop/ms684841(v=vs.85).aspx

Multi-tasking operating systems can have a lot of things going at at once -- they simply dedicate small time slices to each activity;  then switch to the next;  then the next; etc.     These "things" are called threads.

Multi-core processors actually have multiple CPUs -- so there can be two things happening at the same time.

Think of it in human terms ...

You have a lot of activiites to do -- think of each of those as a "thread".    You spend a bit of time on one;  then set it aside and spend a bit of time on the next one;  then the next one;  etc.    Each of those activities is a "thread."     If you had another person helping you, that would be another "core" -- i.e. you could both be working on activities at the same time.

i noticed here cores and threads are 4. is there any instance it may vary.

http://ark.intel.com/products/33081

In "hyperthreaded" processors there will be twice as many hardware threads as there are cores.     These CPUs have two complete sets of registers, so switching between threads is virtually instantaneous (although only one thread/core is active at any one time).

As Intel and AMD develop their CPU, they will be increasing the core and thread count per CPU.

how vcpu is mapped to real CPU in virtualization

what virtualization ? vmware ? in v5 it doesn't actually assign vcpu to physical it slices the cpu resources the main thing in vmware is memory

1 vCPU = A Single Core on the Physical; Hosts Processor (it may not be the same Core, all the time) in simple terms.