1. GCSE Computer Science - Revision
4.2 Hardware
GCSE Computer Science - Revision

3. 4.2.1 Little Man Computer

4. 4.2.1 The CPU
Processors are made of transistors. A transistor is an on/off switch controlled by an electric signal. If you looked inside the CPU they would see a silicon sheet containing thousands of transistors
7.00 – minutes

5. 4.2.1 The CPU
it is the processor clock that sends out a pulse at regular intervals. The clock speed is measured in frequency (cycles per second) using the units hertz. One hertz is one cycle per second. CPUs are so fast they are measured gigahertz (GHz). A 2 GHz clock sends out 2 billion pulses per second. Each clock pulse an instruction is executed in a CPU.
The “ON” and “OFF” sequence showing the clock cycles:
ON (1)
OFF (0)

6. 4.2.1 The CPU
31.04 – 35.05

7. 4.2.1 Single and Multi-core Processors
CPUs tend to be named in families after the company that has designed or manufactured them. Name Intel, AMD Athlon, Broadcom and ARM as examples.
Some processors are now multi-core which means each microprocessor is made up of 2, 4 or 8 separate “core” CPU components. If you look at examples of these multi-core processors you can see the duplicated cores.
In a quad-core processor, each core acts like a single processor. Having four cores allows the CPU to run more than one instruction at the same time. This is called parallel processing.

8. 4.2.1 Memory (RAM – Random Access Memory)
‘volatile’ memory - only retains data while it is receiving electrical power while
‘non-volatile’ memory - retains data even in the absence of a power source (Magnetic, Optical, Solid State).
Main memory (also known as Random Access Memory (RAM)) is volatile and is used to store instructions and data while programs and applications are running. All programs and applications that are running will have data and instructions loaded into RAM.

9. 4.2.1 RAM
Memory addressing - it is helpful to think of memory locations as adjacent ‘slots’ which can hold a piece of data or instructions. The memory is split up into 8 bit (or 1 byte) storage locations. Each storage location is given a unique address.
The size of the address bus determines the maximum number of unique memory addresses that can be used.

10. 4.2.1 Reading From and Writing To Memory
Memory read:
Stage 1
Processor places the address of the required memory location on the address bus
Stage 2
Processor sets the read line on the control bus
Stage 3
Contents of the memory location are conveyed along the data bus into the processor
Memory write
Stage 1
Processor places the address of the required memory location on the address bus
Stage 2
Processor places the data to be written to memory on the data bus
Stage 3
Processor sets the write line on the control bus
Stage 4
The data is conveyed along the data bus to the memory location

11. 4.2.1 Inputs
Input devices - such as microphones, touch screens, and so on. In a mobile phone or tablet, many of the input devices are inbuilt.

12. 4.2.1 Outputs
Output devices - such as monitors, touch screens, printers, speakers, and so on.

13. 4.2.1 Secondary Storage
Secondary storage - is non-volatile and allows programs and data to be stored permanently in between uses in the CPU.
Magnetic – Hard Disk
Optical – CD, BluRay, DVD
Solid State – SSD, USB Memory Stick, SD Cards

14. 4.2.2 Stored Program Concept
Stored Program Concept – The idea was introduced in the late 1940s by John von Neumann, who proposed that a program be electronically stored in binary- number format in a memory device so that instructions could be modified by the computer as determined by intermediate computational results

15. 4.2.2 Stored Program

16. Stored Program Concept
That the stored program concept is the idea that both the instructions and data needed to run a program are stored in the computer’s main memory as binary code. The instructions and the data are then fetched, decoded and executed one after another in a sequence by the computer’s CPU.

17. Von Neumann
This concept was developed by Von Neumann based on the ideas of Alan Turing and is also known as the “Von Neumann architecture”. The stored program concept is used in most digital computers today.

18. Instruction Sets
The instructions needed to run a program are written in an instruction set. An instruction set is a collection of pre-defined “machine codes” which the CPU has been designed to use. Each processor family has its own instruction set.

19. Mid Level Assembly Language (Opcodes and Operands)
Each instruction is referred to with a particular “opcode”. The opcode is a number which indicates that particular type of instruction. Any data needed for that instruction is given as a memory address in the “operand”.
Each opcode is also given a name such as ADD or SUB so programmers can refer to it easily. This language (opcodes and operands) is known as assembly language.

20. Answers

21. Fetch Execute Cycle – Using Assembly Language
Little Man Computer
INP = Input
STA = Store at Address
ADD = Add Contents of address
OUT = Output
HLT = Halt Program
Address
Instruction 00
INP 01
STA 99 02 03
ADD 99 04
OUT 05
HLT

23. 4.2.4 Storing Data on Physical Devices
Magnetic – Hard Disk – Uses a rotating metal ‘Platter’ with rotating magnetic heads (N and S poles represent binary 0 and 1), a moving ‘arm’ on an actuator reads the disk/platter.
(12mins click here)
Optical – CD, BluRay, DVD – Pits burned onto the the platter/disk and inspected with a laser.
Solid State – SSD, USB Memory Stick, SD Cards – Electric charge stored in silicone (No moving parts)
Click here

24. 4.2.5 Microcontrollers
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microcontrollers are small computers usually with a processor, memory and programmable input and output peripherals. Describe how microcontrollers are often embedded to provide automated control systems such as car engine control systems, robots, power tools, games consoles, microwaves, ovens, breadmakers, washing machines, games consoles, digital televisions, mobile phones. etc.

25. 4.2.5 Microcontrollers - Sensors
Sensors are the input devices for many microcontrollers. A sensor as a device that responds to some physical property in its environment such as pressure, temperature, sound levels.
Light sensors, temperature sensors (that measure heat), ultrasound sensors (that measure distance), touch sensors, rotation sensors (that measure the rotation of an axel), accelerometers (that measure motion) and sound sensors…etc
What sensors are used?

26. 4.2.4 and 4.2.1

27. 4.2.4 and 4.2.1

28. 4.2.2

29. 4.2.2

30. 4.2.2

31. 4.2.2

32. 4.2.5

33. 4.2.5

34. 4.2.2

35. 4.2.2