What this it Register Memori

Registers are memory size is very small with very high-speed access. Registers used to store data and instructions are being processed, while that data and other instructions waiting to be processed are stored in
main memory. Registers in the CPU consists of: 
A. Instruction Register (IR) is used to store instructions that are processed.
2. Program Counter (PC) is a register that is used to store the address location of main memory containing the instruction being processed. during the process progresses, the content is converted to PC main memory address containing instructions The next to be processed. This makes it possible to trace The next instruction in main memory.
3. General-purpose registers, the registers that have a wide range of functions associated with the data being processed. For example, if used for accommodate the data being processed is referred to as the operand register, while if it is used to hold the processed result is called the accumulator.
4. Memory Data Register (MDR), which registers are used to hold data or instructions sent from main memory to the CPU, or contain data that saved to main memory as a result of CPU processing.
5. Memory Address Register (MAR) is used to hold data or address instructions on the main memory to be taken or to be placed.

Registered (also called buffered) memory  modules have a register between the DRAM modules and the system's memory controller. They place less electrical load on the memory controller and allow single systems to remain stable with more memory modules than they would have otherwise. Registered memory is often more expensive because of the lower volume and the additional components, so it is usually found only in applications where the need for scalability and stability outweighs the need for a low price (servers, for example). Although most server-grade memory modules are both ECC and registered, there are both registered non-ECC modules and non-registered ECC modules.

Nominally, there is a performance penalty for using registered memory. Each read or write is buffered for one cycle between the memory bus and the DRAM, so the registered RAM can be thought of as running one clock cycle behind the equivalent unregistered DRAM. With SDRAM, this only applies to the first cycle of a burst.