1. Basic Computer Organization Background for CS260

2. Basic Components CPU Main Memory External Memory I/O devices Bus

3. CPU Main Memory VideoDisk Drive All devices communicate through the bus with each other and with the CPU. CPU access of the bus takes precedence. Main Bus

4. CPU – a very simple one! Accumulator Instruction Reg ALU Stack Pointer Flags external bus internal bus

5. 100 101 102 103 104 105 17 106 a b MEMORY addresses values

6. EXAMPLE OPERATION Changing the value of a memory location (decrement by 2) 100 101 102 103 104 105 17 106 a b 104

7. 100 101 102 103 104 105 17 106 a b LOAD value from memory into the CPU’s accumlator 106 accumulator 1.

8. 100 101 102 103 104 105 17 106 a b SUBTRACT 2 from accumulator. Goes through the ALU 106 accumulator 2 106 2 104 2.

9. 100 101 102 103 104 105 17 106 a b STORE the result in the AC into the proper location in main memory Accumulator (AC) 2 104 3.

10. What’s the connection? The operation in c would look like –I = I – 2; The operation in assembly language is –LOAD 101 –SUB 105 –STORE 101 More details involved More hardware knowledge required Not as clear to read/write/understand

11. We want to see the connection! C++ compiler assembly

12. Why? In order to better understand what we are actually instructing the computer to do when we write in the higher level language.