What is cpu register ?

What is cpu register ?
                                                                 Register is a small high speed memory inside cpu .It is used to store data and instruction  temporary.Data is stored in register from main memory for execution .cpu contains a number of register .Each register has a predefined   function .A register can be 1,2,4, or 8 bytes .
special purpose register .
  There are many purpose of register

1  program  counter       (PC)
                   Program counter is used to store the address of the next instruction to be fetched for execution .
2  instruction register     (IR)
                                        Instruction register is used  to store the fetched instruction .
3 Memory address register (MAR)
                                         Memory address register is used to store memory address being used by cpu .
4 Memory buffer register   (MBR)
                                    Memory buffer register is used to store the data coming from the memory or going to the memory. 
5 Stack pointer register