Computer Science 101

1. Computer Science 101 Computer Systems Organization Machine Language Examples Entire machine

2. Hypothetical Lab Machine Memory ALU Control PC(12) IR(16) MAR(12) MDR(16) 16 +1 R(16) ALU GT EQ LT

3. Hypothetical Machine Instructions • Opcode Operation Meaning 0000 Load X Con(X)R 0001 Store X RCon(X) 0010 Clear X 0Con(X) 0011 Add X R+Con(X)R 0100 Increment X Con(X)+1 Con(X) 0101 Subtract X R-Con(X) R 0110 Decrement X Con(X)-1 Con(X)

4. Hypothetical Machine Instructions • Opcode Operation Meaning 0111 Compare X If Con(X) > R CC: 100,etc. 1000 Jump X X  PC 1001 JumpGT X If GT=1, X  PC 1010 JumpEQ X If EQ=1, X  PC 1011 JumpLT X If LT=1, X  PC 1100 JumpNE X If EQ=0, X  PC

5. Hypothetical Machine Instructions • Opcode Operation Meaning 1101 In X Input valueCon(X) 1110 Out X Con(X)Output value 1111 Halt Stop execution

6. 0011000000000110 Add 6 0001000000000111 Store 7 1111000000000000 Halt 0000000000101100 0000000000101100 0000000000001011 0000000000110111 0000000000110111 0000000000000101 Load 5 Machine Language: Con(5)+Con(6)  Con(7) Python: c = a + b 0: 0000000000000101 1: 0011000000000110 2: 0001000000000111 3: 1111000000000000 4: 0000001000001010 5: 0000000000101100 6: 0000000000001011 7: 0000001111111111 1111000011110000 R:

8. Fetch Phase PC MAR Fetch MDR IR PC+1 PC Decode IRop ALU MUX Memory ALU Control PC(12) IR(16) MAR(12) MDR(16) 16 +1 R(16) ALU Micro Steps: Fetch and Decode Phases

9. Load X IRadd MAR Fetch MDR R Store X IRadd  MAR R  MDR Store Memory ALU Control PC(12) IR(16) MAR(12) MDR(16) 16 +1 R(16) ALU Micro Steps: Execution of Load and Store

10. Add X IRadd MAR Fetch MDR ALU R  ALU Add ALU  R Jump X IRadd  PC Memory ALU Control PC(12) IR(16) MAR(12) MDR(16) 16 +1 R(16) ALU Micro Steps: Execution of Add and Jump

11. Compare X IRadd MAR Fetch MDR ALU R  ALU Subtract (set CC) JumpGT If GT=1 IRadd PC Memory ALU Control PC(12) IR(16) MAR(12) MDR(16) 16 +1 R(16) ALU Micro Steps: Execution of Compare and JumpGT

12. If you mean add, just say ADD.