1. CPU Registers PC Arith Logic Unit Bus Interface I/O Bridge System bus Memory bus Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots

2. CPU Registers PC Arith Logic Unit Bus Interface I/O Bridge System bus Memory bus Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots CPU – Central Processing Unit interprets and executes instructions. Buses – electrical conduits which carry bytes (based on word size) between components. Main Memory – temporary storage for the program instructions and its static, automatic, and dynamic memory

3. CPU Registers PC Arith Logic Unit Bus Interface I/O Bridge System bus Memory bus Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots I/O devices such as mouse, keyboard, monitor, and disk are connected to the I/O bus via controllers or adapters. Controllers are typically on the computer’s motherboard; whereas, adapters are separate boards.

4. CPU Registers PC Arith Logic Unit Bus Interface I/O Bridge System bus Memory bus Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots Program Counter (PC) is a special register containing the address of the next instruction to execute. Arithmetic Logic Unit (ALU) performs computations, comparisons, logic, and shifts. Registers are used as high-speed intermediate memory accessible by the ALU.

5. CPU Registers PC Arith Logic Unit Bus Interface I/O Bridge System bus Memory bus Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots The CPU interprets machine instructions (from programs which are in main memory). Some categories of instructions: Loadload registers from a copy of data in main memory or other registers Storestore from a copy of data in registers to main memory

6. CPU Registers PC Arith Logic Unit Bus Interface I/O Bridge System bus Memory bus Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots The CPU interprets machine instructions (from programs which are in main memory). Some categories of instructions (continued): Operateexecute arithmetic, comparisons, logic or shifts using data in registers, storing the result in a register Jumpbranch to an address within a program by changing the PC

7. CPU Registers PC Arith Logic Unit Bus Interface I/O Bridge Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots User types./add2 10 20. Shell causes each keystroke to be brought into a register as it is captured.

8. CPU Registers PC Arith Logic Unit Bus Interface I/O Bridge Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots Shell stores what the user types in Main Memory as he/she types it

9. CPU Registers PC Arith Logic Unit Bus Interface I/O Bridge Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots When user presses enter, the shell makes a request to load the./add2 program into memory. Determining to load./add2 takes steps which we are not showing

10. CPU Registers PC Arith Logic Unit Bus Interface I/O Bridge Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots Execution begins with the Program Counter (PC) set to the beginning address of the program.

11. CPU Registers PC Arith Logic Unit Bus Interface I/O Bridge Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots The CPU fetches an operation at the address in the PC. It then Decodes the instruction to understand the operation and its operands. If necessary, fetches the operands Increments the PC past the instruction Executes the operation

12. CPU 10 20 Registers PC Arith Logic Unit Bus Interface I/O Bridge Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots It loads 10 and 20 into registers based on separate instructions.

13. CPU 10 30 Registers PC Arith Logic Unit Bus Interface I/O Bridge Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots Based on another instruction, the ALU adds 10 to 20, storing the result in a that register.

14. CPU 10 20 Registers PC Arith Logic Unit Bus Interface I/O Bridge Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots Another instruction causes 30 to be written in main memory. 30

15. CPU 10 30 Registers PC Arith Logic Unit Bus Interface I/O Bridge Main Memory USB Controller Graphics Adapter Disk Controller I/O Bus Mouse Keyboard Monitor Disk Expansion Slots Another instruction causes 30 to be displayed on the monitor by taking the value from memory and sending it to the graphics adapter.