1. source: http://thinkgeek.com

2. It’s All (just) Bits 1) Numbers are bits 2) Text is bits
3) Formatted text is bits
4) Pictures are bits
5) Sounds are bits
Paradigm Shift?

3. Bits can be operated on! Example: adding two bits decimal binary
0+0 = = 0 0
0+1 = = 0 1
1+0 = = 0 1
1+1 = = 1 0 2 1
addends
sum
built using by Josh Tynjala

4. It’s All (just) Bits 1) Numbers are bits 2) Text is bits
3) Formatted text is bits
4) Pictures are bits
5) Sounds are bits
6) Programs (instructions on how to operate on bits) are also bits!

5. multiplexer: chooses 1 bit out of 2 using bits!
data bits 1
selector bit
output bit

6. equal to top data bit if selector is 0
data bits
output:
equal to top data bit if selector is 0
equal to bottom data bit if selector is 1
selector bit
built using by Josh Tynjala

7. Computer Architecture in 1 Slide
A program is a sequence of instructions
Both data and program sit in memory (RAM)
At the heart of your computer is a processor, which simply executes instructions in order, one at a time
A processor has a few registers for storing intermediate results (like scratch paper)
There are only a few possible instructions and a few registers; anything more complex is built up from there R1 R3 R5 R7 R2 R4 R6 R8

8. Example Instructions 1. R1  100 2. R2  9 3. R3  R1+R2 4. R8  218
Instructions can be encoded as bits: need a code for each operation (e.g., +=1, =2, /=3) write down the operation code, the values, and the register numbers
100 9
109
109
218 R1 R2 R3 R4 R5 R6 R7 R8

9. Memory
But we have lots of data; it doesn’t all fit into the few registers. It sits in memory.
Big idea: address it.
149
159
150
151
152
153
154
155
156
157
158 … v n o e u m a … …
(lots of) memory

10. How to choose a value by location?
Memory
But we have lots of data; it doesn’t all fit into the few registers. It sits in memory.
Big idea: address it.
How to choose a value by location?
load into R1 the value in memory at address 153 …
149
150
151
152
153
154
155
156
157
158
159 … …
118
111
110 32
110
101
117
109 97
110
110 …
(lots of) memory
110 R1 R3 R5 R7 R2 R4 R6 R8

11. multiplexer: chooses 1 bit out of 2
data bits 1
selector bit
output bit

12. choosing 1 bit out of 4
Set selectors to: 00

13. choosing 1 bit out of 4
Set selectors to:
01 (bottom to top) 1

14. choosing 1 bit out of 4
Set selectors to:
10 (bottom to top) 1

15. choosing 1 bit out of 4
Set selectors to:
11 (bottom to top) 1 1

16. choosing 1 bit out of 8
Addresses:
001
000
010
011
100
101
110
111

17. choosing 1 bit out of 8
Addresses:
001
000
010
011
100
101
110
111 1 1

18. How many layers of multiplexers?

19. (more layers of multiplexers)
Program using memory
1. load into R1 the value in memory at address 153
2. R1  R1  32 …
149
150
151
152
153
154
155
156
157
158
159 … …
118
111
110 32
110
101
117
109 97
110
110 …
(more layers of multiplexers)
110 R1 R3 R5 R7 R2 R4 R6 R8

20. Program using memory
1. load into R1 the value in memory at address 153
2. R1  R1  32
3. store the value in R1 into memory at address 153 …
149
150
151
152
153
154
155
156
157
158
159 … …
118
111
110 32
110
101
117
109 97
110
110 … R1 R3 R5 R7 R2 R4 R6 R8 78

21. Program using memory
1. load into R1 the value in memory at address 153
2. R1  R1  32
3. store the value in R1 into memory at address 153 …
149
150
151
152
153
154
155
156
157
158
159 … …
118
111
110 32
110 78
101
117
109 97
110
110 …
demultiplexers R1 R3 R5 R7 R2 R4 R6 R8 78

22. Program using memory
1. load into R1 the value in memory at address 153
2. R1  R1  32
3. store the value in R1 into memory at address 153 …
149
150
151
152
153
154
155
156
157
158
159 … … v o n
110 N e u m a n n … R1 R3 R5 R7 R2 R4 R6 R8 78

23. Dilbert by Scott Adams, May 8 2005

24. SO WHAT? It’s All (just) Bits 1) Numbers are bits 2) Text is bits
3) Formatted text is bits
4) Pictures are bits
5) Sound is bits
6) Programs (instructions on how to operate on bits) are also bits!