Computer Hardware

Microphone

• Accepts sound input into computer and can convert it to text

• Faster to speak using a microphone than typing and is hands free

• Recognition rate can be slow if there is other noise and files require greater storage

Mouse

• Controls cursor using built in sensors to detect movements and buttons to select

• Easy to use with little to no training and quicker to interact with than a keyboard

• Experienced users find it slower than ‘hot keys’ and needs a flat surface

Graphic digitiser

• Allows hand drawn images on a flat interactive surface with stylus

• More natural to draw diagrams with accurate and detailed drawings

• Not suitable for selecting menus and more expensive than a mouse

Touch screen

• Similar to ordinary screens but with touch sensitive surface, calculating position with x, y

• Not much IT competence required and much faster than a keyboard

• Limited number of options available and can become dirty quickly

Speaker

• Outputs sound, internal or external, and requires a sound card

• Read out text for visually impaired and natural way to communicate

• Requires additional desk space and can distract people surrounding

Laser printer

• Laser beam scans image and attracts ink to reproduce page

• Faster to print in bulk compared to inkjet printers and high quality output

• Colour laser printers are expensive, hard to use and not compact

3D printer

• Gradually prints a solid 3D object one layer at a time

• Time taken to produce an object is much faster with a variety of surfaces

• Limited form of printing, only prototypes, and not economical for large-scale

Hard disk drive (HDD)

• rigid discs stacked on spindle and enclosed, dividing surface into tracks and sectors that rotate at high speeds, back and forth

• Cost per gigabyte is cheaper with a greater capacity

• Prone to breaking down and access speeds are slower than ‘flash’ memory devices as moving parts

Solid state drive (SDD)

• 'Flash memory’ and non-volatile such as USB sticks

• Are compact, portable and have a large storage capacity which does not require a driver

Memory cards

• Electronic flash memory storage devices

• Used in a range of digital devices like mobile phones as a sim

Smart cards

• Bank cards use a form of flash memory known as ‘chip and PIN’

• Contains small embedded IC, allowing data to be written and read with a reader

Fetch stage

1. Memory address held in the PC is copied into the MAR

2. Address bus carries it to the memory

3. It’s instruction is sent back to the MDR via the data bus

Decode stage

1. It is then copied into the IAR and sent to the CU

2. CU finds out what it means (decodes)

3. PC is incremented by 1

Execute stage

1. Now it’s executed, generally the ALU carrying out a calculation

2. Results of processing are stored in the ACC

3. Cycle returns to step one

CPU consists of

high speed memory locations used for specific purposes (registers)

Registers

• Program Counter (PC)

• Memory Address Register (MAR)

• Memory Data Register (MDR)

• Instruction Address Register (IAR)

• Accumulator (ACC)

Program Counter (PC)

stores address of next instruction to be fetched and automatically increments by 1 each time

Memory Address Register (MAR)

temporarily stores address of current instruction or data being executed

Memory Data Register (MDR)

temporarily stores data being fetched from or written to the main memory

Instruction Address Register (IAR)

temporarily stores the current instruction to be decoded and then executed

Accumulator

initially stores results during calculations before transferring to the main memory

CPU

often referred to as the ‘brain’ of the computer, used to process programs and data

How does the CPU work?

repeatedly fetching an instruction from memory and executing it

Components of CPU

control unit, arithmetic and logic unit, immediate access store

Control unit

• Decides which instruction to carry out next and fetches it from memory

• Decodes the instruction to execute

Arithmetic and Logic Unit (ALU)

• Carries out arithmetic calculations

• Makes logical comparisons using operators

Immediate access store (IAS)

• Stores all programs and data temporarily while they are in use

• instructions are fetched from their location using a unique address

Clock speed

measure of instruction cycles in a second, showing speed CPU can process instructions

Unit for clock speed

gigahertz, 3 gHz = 3 billion cycles per second

Cache

temporarily stores frequently used instructions and data, quicker to search through than RAM

Processor core

a single processor, more cores increases ability to run many programs at the same time

Volatile memory

can be read from or written to, whereas non-volatile can only be read

Random Access Memory (RAM)

Stores programs and data currently in use, affecting the speed e.g applications like word

Read Only Memory (ROM)

Stores programs that the computer frequently requires e.g booting up program