Manual input device

• a user needs to physically enter the data into a computer system
  • e.g: a keyboard requires a user to press keys to enter data into the computer

Automatic input device

• will automatically read data and input it into a computer system.
  • e.g: a temperature sensor takes the temperature of a room and inputs it into a computer system automatically (without any user interaction)

Keyboard

A common method of entering data into a computer.

Input method

• each character is represented by a physical key
• mechanical or electrical switches detect key presses and sends a signal

Other details

• can be on-screen (virtual)
• special keys dedicated to other functions
  • e.g: arrow keys

Trackerball mouse

A method of interacting with the computer via cursor.

Input method

on-surface

• moving the mouse rolls the ball fixed on the underside

fixed thumb-ball

• the user may rotate the ball fixed within thumb reach
• this design does not require the mouse to be lifted and repositioned as the ball rolls on the spot

roller ball function

• in the motion of the ball, pickup discs with contacts are spun and touch wires to create pulsing signals

Optical mouse

A method of interacting with the computer via cursor.

Input method

• an LED is shone onto the surface, producing 'hilly' shadows
• a light detector (photodiode array) senses movement by capturing these shadow images
  • a comparison is made between the two images to calculate how far the mouse has moved

Other details

• works best on diffusive surfaces rather than reflective
• can be either wired or wireless

2D scanner

The converted analogue information can be displayed in a document viewer.

Input method

Scanning

• a light source moves across the document and reflects light
  • this light is captured onto a light-sensitive device using mirrors and lenses

Text

• text on the document can be converted to a file using optical character recognition (OCR) software
  • not very reliable; prone to error

Marks

• marks on page can be identified with optical mark recognition (OMR) software
  • can be used to scan handwritten input boxes

3D scanner

Using the scanned information, a 3D model can be created in a modelling software.

Input method

contact - coordinate-measuring machine (CMM)

• the object is probed with a mechanical head that drags a small contact across its surface
  • its geometry is recorded in XYZ space
  • not suitable for few cases; may damage

non-contact - time-of-flight

• scans object by finding the time taken for light to travel to and from surface
• the scanner is rotated to take different points of the object
  • reliable long range, though low accuracy

Microphone

A method of inputting analogue sound information into digital signals.

Input method

dynamic

• a diaphragm vibrates as sound waves travel through
• the vibration causes a coil attached to move in a magnetic field, outputting electric signals

Touchscreen

A method of interacting with the computer system via visual display

Input method

Resistive

• two sheets coated in resistive material are placed together with a thin air gap between
• when contact is made with the touchscreen, the two sheets are pressed together
• the point of contact can be calculated by measuring the voltage gradient across the sheet

Capacitive

• the screen consists of two surfaces, one coated (a small voltage is applied to this one) and the other not
• when a finger touches the uncoated side, the finger acts as a capacitor
• each of the four corners of the screen measure the capacitance difference and determine the location of the touch

Other details

• special functions can be used through multi-touch gestures

RAM

Also known as Random Access Memory.

Holds data and programs temporarily and erased when they are no longer needed.

Differences

• data can be written to and read from
• can range in capacity from a few bytes to several gigabytes
• volatile - loses contents when computer is turned off

Inside a computer

Embedded

• such as a pocket calculator, digital watch or central heating control system may only have a few kilobytes of RAM.
  • this is because they only need to process small amounts of data at a time.

General purpose

• such as desktop PCs, laptops, tablets and smartphones, will have a few gigabytes of RAM.
  • this is because the computer will hold an OS, programs currently running and data that is being processed.

Other details

RAM is often built into peripherals such as printers.

• data to be printed is transferred to the printer’s RAM, then the printer prints the data whilst the computer moves on to other tasks.

ROM

Also known as Read Only Memory.

Stores startup instruction (bootstrap) data, and software.

Differences

• data can only be read from
• typically smaller in capacity
• non-volatile - does not lose contents when computer is turned off

EPROM

Also known as Erasable Programmable ROM.

• data can be written to and read from
• useful in situations where a device’s firmware may need to be upgraded at some point in the future.

HDD

Also known as Hard Disk Drive. Data is

Details

• electromagnetic storage device; made up of multiple disks stacked atop one another
• an actuator arm with a magnetic head moves across each disk, allowing data to be read and written
• random access manner - meaning blocks of data can be accessed in any order

Components

Platter

• the 'disk' is coated in a thin layer of magnetic material, allowing data to be read and written to
• has a high rotational speed (5000 - 7000rpm)
• an HDD usually contains several platters stacked atop one another

Actuator arm

• the arm is mounted to an axis, allowing rotation across the platter
• there are usually one actuator arm per platter disk

Read-and-write head

• affixed to the end of each actuator arm to detect and modify the magnetisation of the material passing directly under
• the distance between the head and platter is minuscule

Other details

RAM is often built into peripherals such as printers.

• data to be printed is transferred to the printer’s RAM, then the printer prints the data whilst the computer moves on to other tasks.

SSD

Also known as Solid State Drive.

Details

• data is stored in integrated circuits which retain data even without power
• do not have disks or moving parts
• larger capacity than HDD

Components

Flash controller

• manages the data stored and the communication with the computer
• controls reading and writing to and from the flash memory

NAND flash memory chip

• do not require power to retain data
• charge is stored in individual cells, effectively storing bits
  • if a cell contains charge, it is denoted as '1', else it is '0'

Other details

• electrical charges which store data will slowly leak over time, resulting in data loss
• prominently used in USB's (hence, flash drive), laptops and smartphones because of their size

Format types

ROM

Read Only Memory

• contents are pre-recorded by manufacturer

RW

Rewritable

• can be erased and rewritten; initially empty

R

Recordable

• can only be written once; initially empty

Optical Disk Drive

• the optical disk is fixed to a rotating axis