1. Computer Processing
CSCE 110
J. Michael Moore

2. Memory
Input
Processor
Output
Storage
J. Michael Moore

3. a.k.a. Central Processing Unit (CPU)
arithmetic/logic unit (ALU)
registers
control unit
Processor
figures out what the ALU should do next
transfers data between main memory and registers
special memory cells that hold data used by ALU and are even faster than cache
performs operations on data (e.g. addition, multiplication)
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4. Processing Bits
Boolean Logic
Applied to circuits
J. Michael Moore

5. Logical AND Truth table Truth table Logic gate X Y X AND Y False True1
Logic gate
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6. Logical AND: An ExampleT F
AND
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7. Logical OR Truth table X Y X OR Y False True Truth table X Y X OR Y 11
Logic gate
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8. Logical OR: An Example T F OR
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9. Logical NOT Truth table X Not X False True Truth table X Not X 11
Logic gate
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10. Logical NOT: An ExampleF
NOT
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11. Logical NAND Truth table X Y X AND Y X NAND Y False True Truth table X1
Logic gate
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12. Logical NAND: An ExampleT F
AND
NAND
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13. Logical NOR Truth table X Y X OR Y X NOR Y False True Truth table X Y1
Logic gate
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14. Logical NOR: An ExampleT F OR
NOR
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15. Logical Exclusive OR (XOR)
Truth table X Y
X XOR Y
False
True
Truth table X Y
X XOR Y 1
Logic gate
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16. Logical XOR: An ExampleT F
XOR
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17. Adder
Half Adder
Full Adder
Ripple Carry Adder
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18. Memory
Input
Processor
Output
Storage
J. Michael Moore

19. How a Program is Executed
Ex: to add the number held in address 3 and the number held in address 6 and put the result in address 10, the control unit
copies data in main memory address 3 into register 1 LOAD 3, 1
copies data in main memory address 6 into register 4 LOAD 6, 4
tells ALU to add contents of registers 1 and 4 and put the result in register 3 ADD 1, 4, 3
copies data in register 3 into main memory address 10 STORE 3, 10
J. Michael Moore

20. How a Program is Executed
LOAD, ADD, and STORE are machine instructions
operation: what action to do (e.g. ADD)
operand: what is affected (e.g. register 3)
How does the control unit know which instruction is next?
The Program
J. Michael Moore

21. How a Program is Stored
Program: list of machine instructions using some agreed upon coding conventions. For example:
first byte
second byte
instruction
operation
code
first
operand
second
operand
third
operand
J. Michael Moore

22. How a Program is Stored Suppose the opcode for ADD is 0010
Then ADD 1, 4, 3 would be encoded as:
Program is stored the same way data is stored. 1
first byte
second byte
instruction
third
operand
second
first
operation
code
J. Michael Moore

23. How a Program is Executed
The control unit has
instruction register: holds current instruction to be executed
program counter: holds address of next instruction in the program to be fetched from memory
J. Michael Moore

24. How a Program is Executed
Program counter tells where the computer is in the program. Usually, the next instruction to execute is the next instruction in memory.
Sometimes we want to jump to another instruction (e.g., an ‘if’ statement or ‘while’ loop). More instructions:
unconditional JUMP: always jump to the address given
conditional JUMP: only jump if a certain condition is true (e.g., some register equals 0 or two registers equal each other)
Instruction to stop executing instructions: HALT
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25. Machine Cycle
Fetch next instruction, as indicated by the program counter (PC), and increment the PC
Decode the bit pattern in the instruction register (IR) - figure out which circuitry needs to be activated to perform the specified instruction
Execute the specified instruction, by activating the ALU to do the right thing. If a JUMP, this may cause the PC to be altered
Typical speeds: 10 to 100 million instructions per second (MIPS)
J. Michael Moore

26. ... ... ... Architecture CPU Control Unit ALU R4 R3 R2 R1 IR PC BUS
First Instruction
Second Instruction
Third Instruction
...
Data
...
... 1 2 3 4
Memory 95 96 97 98 99
J. Michael Moore

27. Assembly Language Example
PC:
IR:
R4:
R3:
R2:
R1:
Memory:
...
12-13: LOAD 108, 3
14-15: LOAD 109, 4
16-17: ADD 3, 4, 1
18-19: STORE 1, 110
20-21: HALT
108:
109:
110: 14 16 18 12 20 22
HALT
STORE
ADD
LOAD
LOAD 35 77
112
112 44 35 77
J. Michael Moore