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2.2 Hardware Considerations

What is Hardware?

Computer hardware is the physical components of the computer. They can be external (such as a monitor or keyboard), or internal (the CPU or RAM).

External hardware devices are used as part of the human-computer interface — they are how we give the computer instructions, and how the computer tells us what it is doing.

Most devices use some form of display to respond to us.

Internal hardware components allow the computer to process and store data. We do not interact directly with them.

Types of Display

Click a button to reveal information about each type of display.

LED
OLED
LCD
ePaper

Light Emitting Diode (LED)

Illustration of LEDs

LEDs are small, low-energy components which light-up when an electrical current is passed through them.

They are bright, durable, and use little power. However, even small LEDs are much larger than the pixels on other types of display.

Common uses: low-energy lighting, displaying simple numerical information (such as the time on a digital clock), or as simple indication lights on devices. Thousands of red, green, and blue LEDs can be used to create huge video walls.

Organic Light Emitting Diode (OLED)

Illustration of a smartphone

Thinner, lighter, and more flexible than LEDs, with much brighter colours and better contrast than LCD.

OLEDs use very little power, which helps battery life. However, they are very expensive!

Common uses: smartphones, smartwatches, and premium TVs.

Liquid Crystal Display (LCD)

Illustration of a TV and calculator

A flat panel containing crystals. When an electrical charge is passed through the crystals, they change opacity between transparent and opaque.

LCDs do not light up, so they must be used in good lighting conditions or with a bright light behind them. The addition of a light (usually white LEDs) adds considerable bulkiness.

Common uses: computer monitors and TVs (with backlight), calculators (without backlight)

Electronic Paper (ePaper)

Illustration of particles in an eInk pixel

ePaper (also called eInk) looks like printed paper, and is excellent for reading in good light. It only uses power when refreshing the image, but the refresh rate is very slow, making it unsuitable for animated graphics.

Most ePaper is black and white, but some newer versions have limited colour capabilities.

Each pixel contains positively charged black particles and negatively charged white particles suspended in a clear liquid. Changing the electrical field causes the particles to rise to the surface so we can see them, or fall to the base where we can't.

Common uses: eBooks and supermarket shelf price tags.

Touch Screens

A touch-layer may be added over a screen. It detects the coordinates of where a user touches the screen and allows the device to determine what has been selected. There are two types: capacitive and resistive.

Capacitive Touch Screens

A glass layer over the display emits an electrical field. When we touch it, our finger disrupts the field and the device can calculate what we selected. Capacitive touch screens are:

  • Accurate
  • Thin
  • Capable of multi-touch gestures (e.g. pinching and swiping)
  • Expensive
Diagram of a capacitive touch screen

Resistive Touch Screens

Two pressure-sensitive layers contain thin conductive wires. When they are pressed together, the wires connect to form a grid which the device can use to calculate what was selected. Resisitive touch screens are:

  • Not as accurate as capacitive layers
  • Durable
  • Able to detect touches even if the user is wearing gloves
  • Cheaper than capacitive touch screens
Diagram of a resisitive touch screen

Display Sizes

Illustration of a monitor

TV and monitor sizes are measured diagonally, usually in inches.

Larger displays use more power and need a more powerful system to calculate content.

Smaller displays are lighter and more portable, but cannot show as much information.

Computer Resources

The more complex the interface, the more computing resources will be needed. These are provided by internal hardware components. Although there are many different types of components, this qualification only requires you to know about processing and RAM.

Processing Power

CPU and GPU

The CPU (central processing unit) is the brain of the computer. It controls everything the device does.

Interfaces with graphics (even simple graphics) will also need a GPU (graphics processing unit), although this may be built in to the CPU.

Embedded systems will have very limited processing capabilities.

Memory

RAM

RAM (random access memory) stores the programs and data currently in use (including any graphics and text data).

Interfaces with graphics require more memory than other types of interface

Quick Quiz

Click the purple circle to select your answer

What are key advantages of LCD displays over ePaper?

LCDs are cheaper to run
LCDs are easier to see in direct sunlight
LCDs support more colours and have faster refresh rates
LCDs are only used in watches
◀︎ 2.1 The Purpose of HCI
▲︎
2.3 Software Considerations ▶︎