the central processing unit and main memory chapter 4, Exploring the Digital Domain The Development and Basic Organization of Computers

based on stored program design processor system –CPU –memory input/output system –input/output devices –secondary storage Electronic Digital Computers

manages the instruction-execution cycle FETCH – DECODE – EXECUTE coordinates the activities of other devices Central Processing Unit

(fast access) storage device for preserving binary data and instructions memory is divided into units or words each is usually a standard size or fixed- length each memory word has a unique address for random access Main Memory

Random Access Memory (RAM) –readable –writable –usually volatile (e.g., Dynamic RAM or DRAM) –general storage Read Only Memory (ROM) –readable –permanent –nonvolatile –special-purpose storage for data and instructions Main Memory

The CPU and Main Memory

Inside the CPU

memory address register memory address register Inside the CPU

memory address register memory address register memory data register memory data register Inside the CPU

memory address register memory address register memory data register memory data register program counter program counter Inside the CPU

memory address register memory address register instruction register instruction register memory data register memory data register program counter program counter Inside the CPU

memory address register memory address register instruction register instruction register memory data register memory data register program counter program counter arithmetic logic unit arithmetic logic unit Inside the CPU

memory address register memory address register instruction register instruction register memory data register memory data register program counter program counter accumulator (work register) accumulator (work register) arithmetic logic unit arithmetic logic unit Inside the CPU

memory address register memory address register instruction register instruction register memory data register memory data register program counter program counter accumulator (work register) accumulator (work register) arithmetic logic unit arithmetic logic unit system clock system clock Inside the CPU

1. address of the next instruction is transferred from PC to MAR 2. the instruction is located in memory 1. address of the next instruction is transferred from PC to MAR 2. the instruction is located in memory FETCH the instruction

3. instruction is copied from memory to MDR 3. instruction is copied from memory to MDR FETCH the instruction

instruction is transferred to and decoded in the IR instruction is transferred to and decoded in the IR DECODE the instruction

control unit sends signals to appropriate devices to cause execution of the instruction control unit sends signals to appropriate devices to cause execution of the instruction EXECUTE the instruction

Data Movement Operations –moving data from memory to the CPU –moving data from memory to memory –input and output Arithmetic and Logical Operations –integer arithmetic –comparing two quantities –shifting, rotating bits in a quantity –testing, comparing, and converting bits Types of Processor Operations

Program Control –starting a program –halting a program –skipping to other instructions –testing data to decide whether to skip over some instructions Types of Processor Operations