A basic description

2. CPU
CU ALU Registers

3. Controls all the operations in the CPU

Transfers data to registers

Directs data to ALU for calculation

Ensures correct paths for data transfer

Synchronisation with the system clock

Click on image to
go to the Fetch-
Execute Cycle

4. Performs calculations

Tests logic functions

Determines relative relationships between values

Click on image to
go to the Fetch-
Execute Cycle

5. Storage register

Stores the next instruction to be executed

Accumulator

Stores the latest results from a calculation

Address register

Stores memory address locations

Instruction register

Stores instructions to be processed
 Click on image to
go to the Fetch-
Execute Cycle

6. The system clock is an accurate, very fast

electronic timer.
The faster the system clock the more

instructions per second are executed.

7. Buses are pathways – separate wires / metallic
strips which transport signals (data).
http://www.webopedia.com/TERM/b/bus.html

8. Fetch:
•The instruction is fetched from memory.
•Instructions are stored in registers.
Decode
•the opcode is decoded by the CU so the instruction can be
executed.
Execute
•The instruction is executed, usually using the ALU.
Store
•The result of the instruction is stored.
Note: this is a simplified explanation (what is required knowledge for the Preliminary course – see link for further
detail).
http://en.wikipedia.org/wiki/Instruction_cycle

9. Decode:
• The typical instruction is divided into two parts: the Opcode
and the Operand
• The opcode is the instruction.
• The operand is the data on which the instruction needs to be
performed.
In the simplified example below:
Add 10
Add would be the instruction (opcode).
•
10 would be the data (operand).
•

10. More input / output devices

Increased processing speed

Larger memory (both primary and secondary)

which is better for working with sound and
graphics