Main memory CPU Arithmetic/Log ic Unit ( ALU ) Control Unit Register(s)
Registers The special storage devices in the CPU that CPU uses over and over again for execution of stored-program instructions. There are two types of registers : –General purpose registers –Special purpose registers
Registers Examples of special purpose registers : –PC ( Program Counter ) –IR ( Instruction Register ) –MAR ( Memory Address Register ) –MDR or MBR ( Memory Data Register or Memory Buffer Register ) –PSW ( Program Status Word ) –etc.
R0 R1 MDR IR MARPC ALU RN Control unit Data bus Control bus Address bus CPU Main Memory
Main Memory Operations Memory read operation –Transfers the content of a specific main memory location to the CPU. –The content of the main memory location remains (unchanged).
Memory write operation –Transfers a word of information from the CPU to a specific main memory location. –Destroys the former content of the main memory location. Memory access time –The time it takes to perform a memory read or a memory write operation. Main Memory Operations