Chapter 2: Computer Hardware

Question 1

Hardware

Answer 1

The physical components of a computer. Anything that that can be seen, or touched.

Question 2

Computer architecture

Answer 2

The architecture is the logical structure, and organisation of the computer hardware.

The von Neumann structure is the basis for all modern digital computers.

All data, and instructionas are stored in RAM as binary numbers.

Question 3

What are the two main components of the Central Processing Unit?

Answer 3

• ALU (Arithmetic, and Logic Unit): carries out all of the arithmetic, and logical operations e.g. addition, comparison
• Control unit: uses electrical signals to direct the system to run instructions in programs, and control the flow of data in the CPU.

Question 4

The fetch-execute cycle

Answer 4

1) Fetch the instruction from memory.
2) Decode the instruction to find out what processing to do.
3) Execute the instruction.

This is an endless cycle that starts once the CPu is turned on.
The programs the CPU needs to process are stored in main memory/RAM.
The computer can only do one cycle at a time, it just does it incredibly quickly.

Question 5

Boot program/sequence

Answer 5

When the CPU is switched on it looks in ROM to load the first program, and execute it. This is called the boot program.

This runs a few basic processes to get the CPU up, and running, and also gets the operating system started.
Once this is done it hands over control to the operating system.

Question 6

Clock speed

Answer 6

The constant frequency that all of the computer’s processes are synchronised to. It is measured in Hz/cycles per second, and tells you how many processes are executed per second.

1 MHz = 1 million cycles per second.
1 GHz = 1 billion cycles per second.

Question 7

Cache memory

Answer 7

Cache is very fast, and expensive memory. It holds data close to the CPU, and works at the same speed as the CPU. It only holds the single next piece of data to be processed.

Question 8

Multiple processor cores

Answer 8

This means that the computer had multiple CPUs working simultaneously.

The CPUs can call fetch, decode, and execute processes at the same time so the computer can execute more processes per second e.g. 3 GHz + 3 GHz = 6 billion cycles per second.

+ive: more data processed at once.
-ive: more complicated operating systems are needed to manage them.

Question 9

Bus

Answer 9

A circuit of wires that transport data, and connect the parts of the motherboard.

The speed of a bus is measured in MHz (millions of cycles per second), and refers to how much data can move across the bus at the same time.

Question 10

Which three things change the speed at which the CPU can process data?

Answer 10

Clock speed (processor speed)

Cache memory

Number of cores

Question 11

RAM (Random Access Memory)

Answer 11

This is the main memory. It temporarily stores data, and programs that are currently being processed. It is volatile.

It can be accessed, and changed by the computer at any time.

It stores the operating system, and is very large.

You can add more RAM to make more memory available, and improve performance.

Question 12

ROM (Read Only Memory)

Answer 12

This cannot be writted to, is non-volatile, and stores the boot program (performs basic checks, finds the operating system, and hands over control to the operating system).

Also, it is small.

You can change the type of ROM/operating system using a process called flashing.

Question 13

CPU

Answer 13

Central Processing Unit. The purpose of the CPU is to fetch, decode, and execute instructions.

Question 14

Primary memory

Answer 14

The only memory that the CPU can access directly, it stores the data, and instructions to be processed.

There are two types of primary memory: RAM, and ROM.

Question 15

Virtual memory

Answer 15

The part of the hard drive used as an extension to RAM when the computer doesn’t have enough RAM to hold all of the data, and instructions required.

Accessing the hard disk is MUCH slower than accessing RAM.
This means that if virtual memory is constantly being used the computer’s speed is significantly decreased.

To overcome this quit some programs, or add extra RAM to your computer.

Question 16

What are the two types of RAM?

Answer 16

• Dynamic RAM= can only hold a charge for a few milliseconds, and must constantly be refreshed.
• Static RAM= access times are faster as it doesn’t need to be constantly refreshed, but is more complex, and expensive. Static RAM chips are used for cache memory.

Question 17

Flash (solid state) memory

Answer 17

A type of ROM that can be rewritten by flashing (applying an electrical charge to the part of the circuit you want to re-write).

Flash memory is used as a portable medium for storing, and transferring data e.g. USB memory sticks, cameras, phones.

Access times are not as fast as RAM, but are faster than hard disks.

• Good capacity (but less than hard disk)
• Used in hand held devices
• More expensive than hard disk

Question 18

Binary logic

Answer 18

NOT logic gate (Right facing arrow)
- Does the opposite. If you input 1, output is 0, and vice versa.

AND logic gate (Curved with two input strands)
- If the two inputs are the same then it is that, else it is 0.

OR logic gate (Curved arrow- like a spaceship with two input strands)
- If either of the inputs are 1, the output is 1.

Think of 1 as an on switch, and 0 as an off switch.

Question 19

Input devices

Answer 19

Typical home, or office computer:

• Keyboard: manual data entry, can be seperate, or built in.
• Mouse: controlling a pointer to select, open, move, or edit.
• Touch screen: to perform as a mouse, but with a wider range of gestures.
• Microphone: for voice input to communicate, or to issue voice commands to the system.
• Camera: for image capture e.g. photos, webcam
• Scanner: to scan in documents, and images from hard copy sources.

Businesses:

• Bar code readers: to scan labels to identify items, and retrieve data from a database.
• RFID readers (Radio Frequency Identification): like an electronic barcode that can be read at a distance, and doesn’t need a line of sight. Often used in shops to track items past sensors.
• Sensors: e.g. in an aeroplane to monitor, and feedback to the control system that then alters settings.

Disabilities:

• Eye-typer: detect eye movements, and blinking.
• Puff-suck switch: operate switches by sucking, and blowing into a tube.
• Voice input: spoken commands.
• Joystick: requires less physical movement than mouse.
• Foot mouse: for limited arm movement.
• Braille keyboard: for blind people.

Question 20

Output devices

Answer 20

Typical home, or office computer:

• Monitor: to display the results of processing. LED, or LCD.
• Speakers/headphones: for audio (music, feedback, warnings, and communication) e.g. hospitals can issue an audio warning on the patient’s vitals.
• Printer: for hard copy evidence. Often laser for documents, and ink jet for high quality colour images.

Specialised:

• Plotters: for producing technical drawings in design, or architecture.
• Thermal printers: fewer moving parts than lasers, or ink jets so it is silent in operation.
• Actuators: to adjust parts of the system (aeroplanes).

Disabilities:

• Sreen readers: speech software reads the display on screen.
• Voice synthesisers: provide spoken output using user’s text input.
• Actuators: provide physical movement in response to the computer.

Question 21

Magnetic hard disk

Answer 21

Stores the operating system, installed programs, and user data.

• Reliable
• High capacity at low cost
• Good access speed

Question 22

Optical disk

Answer 22

Excellent for transferring files, or distributing software.
CD/DVD ROM: distribute programs.
CD/DVD R/W: store, transfer, or back up data, and programs.

• Good capacity
• Small- easy to distribute
• Robust- can be used multiple times
• Slower than hard disk, and flash ROM

Question 23

What should you consider when choosing secondary stroage?

Answer 23

Data capacity
Speed
Portability
Durability
Reliability