Input/Output and Storage

CH3 of OCR A-Level Computer Science

Important Display Specifications

Resolution (The Number of Pixels), Dot Pitch (The Spacing Between the Centre of Each Pixel), Response Time (How Long it Takes to Change Colours), Refresh Time (How Often the Entire Screen is Redrawn), Colour Support (How Many Different Colours can be Represented), and Brightness (How Much Light can get through the Screen).

Magnetic Hard Drives (HDDs)

The most common type of hard drive, Made of spinning platters and a read/write head to address physical locations of storage.

Solid State Drive (SSDs)

A type of HDD that has no moving parts, it is more efficient and has better portability. It produces no noise, requires little power, and emits very little heat.

Optical Disks

They are read using a laser that reflects on ‘pits’ and ‘lands’ that form a spiral on a disc. The three types are CD, DVD, and Blu-Ray.

Server Storage

A collection of HDDs to form a logical drive, data is shared between multiple discs.

Projectors

Projectors have LCDs inside them, newer and better ones have three. They are lit by either LED or Halogen lamps.

Radio Frequency Identificaton (RFID)

These are tiny sticky labels that can be concealed within products, they are used in various different ways. E.g. Key cards to open doors.

Organic Light Emitting Diodes (OLED)

They directly emit light, they dont need any energy. With an active matrix they are called AMOLEDs. They can suffer from burns where blue pixels fail on a chemical level.

Inkjet Printer

Small holes under the ink cartridge to dispense ink, using electrical charges it vibrates a crystal, ink droplets are dispensed depending on charge strength. Each colour is determined quantity and this is released in designated sections. Different inks mix to make different colours.

Laser Printer

Charging rollers apply negative chargers to the OPC drum, the laser applies positive charge to all the areas that nk will go, toner is then applied by the developer roller. The transfer roller will pull toner with negative charges, the toner is baked then pressure rolled.

Thin Film Transistor Displays (TFTs)

An active matrix (grid of rows and columns of wires), addresses each pixel. Colour filters make sure light coming through is the right colour for its pixel.

Liquid Crystal Display (LCDs)

Layers 1 and 5 → Polarising Filters, they are perpendicular to each other to block light.

Layers 2 and 4 → clear glass with indium tin oxide, and electrodes to change.

Layer 3 = Twisted nematic liquid crystal - when a current is applied it will rotate light passing through by 90 degrees.

Layer 6 → Reflective Backlight.

QR Codes

A type of 3D barcode, can store more data, up to 7089 numbers of 4296 characters. These work by image not laser.

Flatbed Scanner

Allows the user to scan physical documents and save them digitally.

Optimal Mark Recognition (OMR) Scanner

Used to input the answers or marks that a candidate has marked on a multiple choice exam paper.

Check Digits

An extra digit at the end of a number that is computed from the other digits.

Barcodes

Laser light from the scanner is reflected by white lines, photoelectric cells process this to create a binary number corresponding with the code.

Smart Chip Reader

Reads the data from an embedded integrated circuit (IC) chip, used in bank cards.

NFC (Near Field Communicator) Reader

Reads the data from a NFC tag, used for contactless payments.

Keyboards

Membrane → One single membrane under all the keys that responds to the interactions of the user.

Mechanical → Each key has its own trigger to respond to interaction.

Touchscreen Devices

Resistive → A plastic touchscreen, to press it use a stylus or apply pressure.

Capacitive → A glass touchscreen, sensitive to touch.

Mouses

Optical → uses lasers to track its movement and respond to it.

Ball → Uses a ball to track direction and movement.

Track Pads → Flat, user uses finger to move the cursor.

Track Balls →Still ball that is moved to move the cursor.

Interactive Whiteboard

Allows for notation/annotation or any interaction on a whiteboard. Can use grids or sensors to track interactions.