1. Central Processing Unit
CPU
Central Processing Unit
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2. 3.2 Components of the CPU Control unit Arithmetic logic unit (ALU)
Moves data and instructions between main memory and registers
Arithmetic logic unit (ALU)
Performs computation and comparison operations
Set of registers
Storage locations that hold inputs and outputs for the ALU 2

3. 3

4. CPU Structure CPU must: Fetch instructions Interpret instructions
Fetch data
Process data
Write data 22

5. CPU With Systems Bus

6. CPU Internal Structure

7. Actions Performed by CPU
Fetch cycle
CPU:
Fetches an instruction from primary storage
Increments a pointer to location of next instruction
Separates instruction into components (instruction code and data inputs)
Stores each component in a separate register
Execution cycle
ALU:
Retrieves instruction code from a register
Retrieves data inputs from registers
Passes data inputs through internal circuits to perform data transformation
Stores results in a register 7

8. Register
A, special, high-speed storage area within the CPU. All data must be represented in a register before it can be processed.
For example, if two numbers are to be multiplied, both numbers must be in registers, and the result is also placed in a register.
The power and speed of a CPU determined by
the number of registers that a CPU has and
the size of each (number of bits)
For example a 32-bit CPU is one in which each register is 32 bits wide. Therefore, each CPU instruction can manipulate 32 bits of data. 8

9. Registers
Fast stand-alone storage locations that hold data temporarily in CPU.
PC (Program Counter)
Keep track of the instruction currently being executed.
Incremented after execution of the instruction.
Instruction Register
Store the instruction currently being executed
Data Registers
Hold data before it can be processed 9

10. CPU Registers Primary roles
Hold data for currently executing program that is needed quickly or frequently (general-purpose registers)
Store information about currently executing program and about status of CPU (special- purpose registers) 10

11. General-Purpose Registers
Hold intermediate results and frequently needed data items
Used only by currently executing program
Implemented within the CPU; contents can be read or written quickly
Increasing their number usually decreases program execution time to a point 11

12. Special-Purpose Registers
Track processor and program status
Types
Instruction register
Instruction pointer
Program status word (PSW)
Stores results of comparison operation
Controls conditional branch execution
Indicates actual or potential error conditions 12

13. ALU Arithmetic operations: Logical operations: Increment Decrement Add
Subtract
Multiply
Divide
Logical operations:
NOT
AND OR
XOR 13

14. Control Unit
Like the part of the human brain that control the operation of each part of the body.
Controlling is achieved through wires (form Control unit to ALU) that can be on/off.
4 wires  16 operations 14

15. A B C 10 20 30 CA+B ADD I ← M[PC] PC++ R1 ← A R2 ← B R3 ← R1 + R2.
2000
CA+B
2004
CC-5 10 A 20 B 30 C 10 20 30
CA+B
ADD
2000

16. 3.3 The Physical CPU
Electrical device implemented as silicon- based microprocessor
Contains millions of switches, which perform basic processing functions
Physical implementation of switches and circuits 16

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