1. Pigeon Hole Device What does it resemble? What can it do? How could it be improved? Will it ever look familiar? How much ‘memory’ does it have? What kind of problems does it have?

2. 1 2 3 4 5 6 7 8 9 Nine empty boxes numbered from 1 to 9. 1

3. 1 MOVE 9 TO 6 2 MULTIPLY 8 BY 6 3 SUBTRACT ‘1’ FROM 7 4 IF 7 NOT = ‘0’ GO TO 2 5 STOP (Answer in 6) 6 Value 7 Value 3 8 Value 1.05 9 Value 5000.00 Lets put something in the boxes and see what happens. 1

4. 1 MOVE 9 TO 6 2 MULTIPLY 8 BY 6 3 SUBTRACT ‘1’ FROM 7 4 IF 7 NOT = ‘0’ GO TO 2 5 STOP (Answer in 6) 6 Value 5000.00 7 Value 3 8 Value 1.05 9 Value 5000.00 After execution of first command in box 1. 2

5. 1 MOVE 9 TO 6 2 MULTIPLY 8 BY 6 3 SUBTRACT ‘1’ FROM 7 4 IF 7 NOT = ‘0’ GO TO 2 5 STOP (Answer in 6) 6 Value 5250.00 7 Value 3 8 Value 1.05 9 Value 5000.00 After execution of command in box 2. 3

6. 1 MOVE 9 TO 6 2 MULTIPLY 8 BY 6 3 SUBTRACT ‘1’ FROM 7 4 IF 7 NOT = ‘0’ GO TO 2 5 STOP (Answer in 6) 6 Value 5250.00 7 Value 2 8 Value 1.05 9 Value 5000.00 After execution of command in box 3. 4

7. 1 MOVE 9 TO 6 2 MULTIPLY 8 BY 6 3 SUBTRACT ‘1’ FROM 7 4 IF 7 NOT = ‘0’ GO TO 2 5 STOP (Answer in 6) 6 Value 5250.00 7 Value 2 8 Value 1.05 9 Value 5000.00 After execution of command in box 4. 2

8. 1 MOVE 9 TO 6 2 MULTIPLY 8 BY 6 3 SUBTRACT ‘1’ FROM 7 4 IF 7 NOT = ‘0’ GO TO 2 5 STOP (Answer in 6) 6 Value 5512.50 7 Value 2 8 Value 1.05 9 Value 5000.00 After execution of command in box 2. 3

9. 1 MOVE 9 TO 6 2 MULTIPLY 8 BY 6 3 SUBTRACT ‘1’ FROM 7 4 IF 7 NOT = ‘0’ GO TO 2 5 STOP (Answer in 6) 6 Value 5512.50 7 Value 1 8 Value 1.05 9 Value 5000.00 After execution of command in box 3. 4

10. 1 MOVE 9 TO 6 2 MULTIPLY 8 BY 6 3 SUBTRACT ‘1’ FROM 7 4 IF 7 NOT = ‘0’ GO TO 2 5 STOP (Answer in 6) 6 Value 5512.50 7 Value 1 8 Value 1.05 9 Value 5000.00 After execution of command in box 4. 2

11. 1 MOVE 9 TO 6 2 MULTIPLY 8 BY 6 3 SUBTRACT ‘1’ FROM 7 4 IF 7 NOT = ‘0’ GO TO 2 5 STOP (Answer in 6) 6 Value 5788.13 7 Value 1 8 Value 1.05 9 Value 5000.00 After execution of command in box 2. 3

12. 1 MOVE 9 TO 6 2 MULTIPLY 8 BY 6 3 SUBTRACT ‘1’ FROM 7 4 IF 7 NOT = ‘0’ GO TO 2 5 STOP (Answer in 6) 6 Value 5788.13 7 Value 0 8 Value 1.05 9 Value 5000.00 After execution of command in box 3. 4

13. 1 MOVE 9 TO 6 2 MULTIPLY 8 BY 6 3 SUBTRACT ‘1’ FROM 7 4 IF 7 NOT = ‘0’ GO TO 2 5 STOP (Answer in 6) 6 Value 5788.13 7 Value 0 8 Value 1.05 9 Value 5000.00 After execution of command in box 4. 5

14. 1 MOVE 9 TO 6 2 MULTIPLY 8 BY 6 3 SUBTRACT ‘1’ FROM 7 4 IF 7 NOT = ‘0’ GO TO 2 5 STOP (Answer in 6) 6 Value 5788.13 7 Value 0 8 Value 1.05 9 Value 5000.00 After execution of command in box 5. Stopped! 0

15. Ring any bells? What does it look like? Initialize, Loop, Terminate (Which box) Variables, Constants, Values? How could we improve the ‘model’

16. Improvements? Labels, Identifiers, Names for stuff Memory contents? Fixed / Variable Registers? Indirect addressing? (Box 1) Move (Box7) to Box 3 Outside I/O (Files, etc?) I/O Commands (Read and Write?)