1. Components of a CPU
AS Computing - F451

2. Microprocessor

4. “640kb ought to be enough for anybody”
Bill Gates, 1981

5. Control
Unit
ALU
Memory
Unit
(IAS)
Registers PC
MAR MDR
CIR

6. Interrupt
A signal telling a piece of software to “wait” whilst another, more important command is executed.
What are some examples?

7. Buffer
A region of memory that is temporarily used to hold data while it is being moved form one place to another
Used when 2 devices transmitting to each other run at different speeds
Buffers can be implement in either hardware or software

8. ALU – Arithmetic Logic Unit
Where calculations are carried out
Mathematical & Logical operations
Instruction Set
Acts as a gateway to and from the processor

9. Control Unit Controls the data flow in the processor
Controls the fetch execute cycle
Synchronises actions (using inbuilt clock)
Sends control signals to other parts of the processor

10. Memory Unit (IAS) Purpose of RAM Store part of currently in use
operating system
program
data
currently in use

11. Non Volatile! Purpose of ROM Purpose of ROM Start up program
Bootstrap Program.
Non Volatile!

12. communication to send data
Buses
Channel of
communication to send data

13. Buses
Data Bus
This is used to carry the data that needs to be transferred from one piece of hardware to another

14. Address Bus
Carries identification about where the data is being sent/coming from

15. Control Bus
This carries the command signals of the control unit to other components

16. Registers “Locations in memory used for specific purposes”
What is a Register?
“Locations in memory used for specific
purposes”

17. IAS Program Counter Current Instruction Register Memory Address
Data
Register
Stores where in IAS the next instruction is
Stores the current instruction being executed
Stores the address of where the data used in the current instruction
Acts as a buffer between the IAS and CPU

18. Register Definitions Program Counter Current Instruction Register
stores the address of the next instruction
Current Instruction Register
stores the instruction currently being operated on
Memory Address Register
stores the address in memory currently being accessed
Memory Data Register
stores the data being transferred to or from memory

19. External components
The term external components refers to the parts that you physically interact with.
These are also known as peripherals or input/output devices and include the:
keyboard
monitor
printer

20. Internal components
The term internal components refers to the components contained within the casing of the computer.
They include the:
processor
memory (RAM and ROM)
hard disk.

21. Types of Memory Random Access Memory (RAM)
Immediate access store (IAS)
It temporary stores data used by applications that are running.
The contents are lost when the computer is switched off.
Volatile
Read Only Memory
(ROM)
ROM is a permanent storage area which cannot be changed by the user.
ROM contains the start up software (this makes the PC boot up)
Non-Volatile

22. Read Only Memory
Non-Volatile – Contents of memory is not erased when hardware is powered off.
Contains Start up program
Start up program is required immediately when power is switched on

23. Random Access Memory
Volatile – Contents of memory is erased when hardware is powered off
Contains applications software currently being used, OS files
Allows changes to be made to saved contents
Fast access to data

24. Transferring Data – Primary Memory to Secondary Storage

25. This exact question has come up in 2 previous past papers, and can be worth 6+ marks.
“Describe the use of interrupts and buffers when data is transferred from primary memory to a storage device.”

26. Define Terms Primary Memory – RAM, IAS
Secondary Storage – USB Memory Stick
Both transfer data at different speeds
Therefore need to use
Buffer
Area of temporary memory used to transfer data between 2 devices
Interrupt
Method of stopping the CPU so it can perform a task and return to the previous task.

27. Key Points Data sent to buffer from primary memory.
This allows processor can continue with other tasks
Interrupt sent when buffer is full.
Buffer is emptied to storage device.
Buffer used to allow RAM and secondary storage device to transfer data as they do so at different speeds.
When buffer is empty
Interrupt is sent to processor
To request buffer refill
Process cycles until all data is transferred

28. Additional Points Error checking takes place once data is transferred.
Interrupt given priority to CPU when buffer is full, required refilling
Plan your answer. Use clear English. Read it first before writing on question paper. EXAM Technique!