External components
Overview of many external components, or peripheral devices, used by and for computers. Input devices, Output devices, and connectors
Introduction
Last week we learned the basic behaviors that define computers – their ability to store, retrieve, and process information. This means that many simple devices, even non-electronics, can be considered computers.
The computers that we mostly are concerned with in the computer science profession, however, are generally complicated electronic devices made of many components. In this class, we are going to learn many of the fundamental components that make up modern computing devices.
Today, we will start with the external, or peripheral, components of a computer – each of these have their own set of interesting behaviors and properties that are worth understanding.
Many peripheral components of a computer can broadly be divided into two categories:
- Input Devices: devices that accept data and instructions from a user to a computer.
- Output Devices: devices that present data and information to the user from a computer.
We will cover many examples of each.
Lesson overview
Learn the history, behavior, and important properties of Input and Output devices
- Input devices:
- Keyboards
- Mice
- Controllers
- Cameras
- Touchscreens
- Scanners
- Output devices:
- Monitors
- Projectors
- Printers
- Speakers
Input Devices
Input Devices are devices that accept data and instructions from a user to a computer.
Mouse
Used to navigate the graphical user interface (GUI). There are many types of mice, distinguished by tracking technology and by use case
Technology:
- Mechanical mice use a ball to measure movement (obsolete now – why?)
- Optical mice use light sources (first LED, then more precise Laser).1
Purpose:
Many! “Gaming” (many buttons), Ergonomic (optimize human comfort), etc.
Keyboard
Used to enter text commands. Most commonly used is the QWERTY layout (used in typewriters since 1873). Other layouts include QWERTZ (Germany/Switzerland) and AZERTY (France) and DVORAK (nerds2)
Variations include wired or wireless keyboards and numeric keypads. Ergonomic designs are recently becoming more popular.
Input Devices: Others
- Gamepads or joysticks are used for playing games and running simulations.
- Digital / video cameras and webcams create images and videos.
- Biometric devices use features unique to an individual user (e.g. fingerprint).
- Touchscreens have a pressure-sensitive panel.
- Scanners digitize images or documents so they can be stored as files.
- Digital Tablets (sometimes called Digitizers) allow the user to create images or artwork using a stylus.
- Media card readers read/write data from/to different types of media cards (SD cards, video game cartridges, etc.)
Output Devices
Output Devices are devices that present data and information to the user from a computer.
Monitors
There are many different types of monitors use different technologies to create an image. However, the common principles are the same:
- Digital representation of image to display is sent to the monitor
- The monitor produces each pixel (the “atom” of monitor displays) using some deterministic physical technology
- Light from the monitor reaches us as a useful/pleasing image.
The following sections are the main technologies used today (from oldest to newest)
Cathode Ray Tube (CRT)
Cathode Ray Tube (CRT) monitors are very complicated, very cool, moderately dangerous, and mostly obsolete!
- The most common type of consumer and industry television before ~2010
- Basically: a tungsten coil is heated in a vacuum until it sheds electrons, those electrons are accelerated by an electric field and guided by magnets to hit a phosphor coated glass display to emit light in a pixel grid
- Obsolete since today their are lighter, simpler higher resolution technologies
- Still used today for some applications due to zero latency . For instance, I use one for playing NES Tetris!
Plasma
Plasma monitors use tiny cells of ionised gas that light up when stimulated by electricity.
- Often used in home theatre applications due to accurate video representation.
- High levels of brightness, deep black levels and very wide colour range.
- Have shorter life span, susceptible to “screen burn-in” (this is why screensavers are called “screen savers”! Same for CRT).
- (+) Plasma cell will produce light that looks good from every angle, it was high refresh rate (videos are smoother)
- (-) BUT! Consumes a lot of electricity
- (-) Doesn’t work at high altitudes! (low pressure)
Liquid Crystal Display (LCD)
An LCD Screen is made up of layers of very thin glass, liquid crystal, metal and dielectrics. Liquid cystal is a modelcule between liquid (not ordered and constant motion) and crystal (ordered fashion). This technology allows for precise control of color without the need to ionise gas with powerful electronics.
- Commonly used in flat panel monitors and laptops.
- Consists of a white backlight (in light, white = all colours combined), two polarizing filters, and liquid crystal solution between them to transform the backlight into a coherent pixel grid.
- An electronic current aligns and controls the crystals so that light can pass through them.
- (+) Allow the use of flat screens!
Light emitting diode (LED)
- An LCD display that uses LED backlighting instead of a white backlight to light the display. The brightness of each RGB LED is controlled programmatically to produce each pixel
- (+) Thinner (no layers), lighter and brighter, and displays better contrast
- (+) Lower power consumption.
For more information: https://www.youtube.com/watch?v=Gx-JVoOFYhs&ab_channel=e-learning%C3%A9lectronique
Organic LED (OLED)
OLED displays are similar to LED, but no backlighting required – the material used to create these displays emits light when an electrical current is applied.
- Similar to LED, but no backlighting required – the material used to create these displays emits light when an electrical current is applied .
- (+) Allows for perfect representation of dark colors unlike all other monitor technologies. Also allows for flexible and transparent monitors
- (-) More expensive to produce, more susceptible to screen-burn-in than LCD or LED (but better than Plasma and CRT in this respect)
Here’s a great video (8 mins) explaining both physical and software technologies required to make the above monitors work: https://www.youtube.com/watch?v=uyLDA9QT8EY
With LCD, LED, and OLED, we finally get to the most modern monitor technologies. These are used in our labs, most computers, laptops. They’re ordered here approximately in order of lowest (LCD) -> highest (OLED) quality, though pros and cons exist for each.
See here for more information: https://en.wikipedia.org/wiki/Comparison_of_CRT,_LCD,_Plasma,_and_OLED_displays.
Printers
Printers take data from a computer and generate output on paper: Basic principles
- Similar to monitor (high quantity of small, well placed “pixels” → the visual quality of a coherent image)
- Rather than orienting light photons on a screen, printers deposit liquid stains on to paper. The physical setup is different, but the same principles are at work.
Dot-matrix printers
- Uses print heads containing pins which produce patterns of dots on the paper by mechanical impact (pressing).
- Inexpensive and typically print at a speed of 100 - 600 characters per second.
- (Optional) See https://en.wikipedia.org/wiki/Dot_matrix_printer for more detail on history and technology
- While still in use for particular applications (printing receipts for e.g.), these are now obsoleted by…
Ink-jet printers
- Uses tiny droplets of ink to produce images.
- Heat is applied to an ink reservoir, which pushes ink bubbles through a nozzle in a controlled manner.
- The ink liquid droplets are smaller in diameter than a human hair! Many of these added together produce the quality of a coherent image.
- Quieter than dot-matrix, and also provide better speed and higher quality.
Laser Printers
- Expensive when they were initially introduced.
- Produce high-quality output quietly at a high speed.
- Produces images by directing a laser beam at a mirror which bounces the beam onto a drum.
- The drum contains a special coating to which the toner (ink powder) sticks.
- A laser beam then conveys information to the drum, neutralizing and detaching some toner.
- As the paper rolls by the drum, the toner is transferred onto the paper. A hot roller then bonds toner to the paper.
Connectors
Connectors are how to get the computer to talk to all these output devices!
Cables
Some technical terms:
- Cable (electric) : The insulated copper wire that carries electrical/digital signals from devices to/from computers
- Cable (optical) : The insulated glass tube that carries digital signals in the form of light between devices and computers
- Port : The slot where the insertable end of USB cable is connected to the computer
- “Male” / “Female” cable ends : Distinguishing between the insertable end and the receptacle end for cables
- Converter : A device that allows different standards/types of connectors to be used together
Electrical cables
transmit an electrical signal on a conducting wire, insulated to protect the signal/surroundings
Optical cables
transmit signal in the form of light. Very fast! (speed of light in glass).
A short paper (5 pages) comparing the two cable technologies in more detail: Fibre Optics vs Copper Cabling: Understanding the Differences
USB
Universal Serial Bus (we’ll talk about the meaning of the last two words soon!) is used to connect most modern devices to computers. Back in the day, mice/keyboards/external storage/speakers/etc. all had different cables. These have now been (mostly) unified under the USB standard.
USB connectors can transmit both power (e.g. charging phones) and information (data). Despite being “Universal” there are an incredible number of USB types.
USB “Number” standards refer to the transmission speed and power of the cables
- e.g. USB 3 is faster/more power than USB 2 and USB 2
USB “Letter” standards refer to the physical design of the connector and the port
- e.g. USB C and USB A are incompatible interfaces, cannot be interchanged.
Audio
Most commonly the standard headphone jack (TSR connector). Available in several sizes, most commonly 3.5mm or ⅛” mini audio jack. Can be color coded - microphone (pink), speaker (green).
For higher-end audio, we can use fiberoptic cables as these can transmit larger amounts of data more quickly, which is required for producing a high-quality audio signal.
Video
VGA cable is commonly used for computer monitors (15-pins). Low resolutions, now obsolete. There exist converter cables to connect VGA monitors to newer computers.
MiniVGA is a variant found on laptops.
DVI was once the common modern upgrade from VGA, capable of higher resolutions. MiniDVI and MicroDVI on “thin” laptops.
S-Video commonly used for DVD players, camcorders and older consoles.
RCA cables include composite video (yellow) and stereo audio cables (red for right; white/black for left). Component video offers a better picture.
HDMI is the new standard for audio and video transmission in a single cable.
DisplayPort (and Mini DisplayPort) more commonly used in computers.
Data
eSATA is used internally to connect the hard drive to the motherboard but can also be used for portable hard drives.
Networking
Telephone cable (RJ11) used for connecting to the internet through DSL/ADSL modems. Standard phone cable has 4 wires; connector has 4 pins. Clip helps to maintain tight connection.
Ethernet (RJ45) is the standard for wired networking. Based on Cat5 twisted pair cable, made from 8 individual wires. Connector looks similar to phone plug but is thicker and wider. Also uses a clip to maintain tight connection.
Exercises
Knowledge check
Additional resources
Footnotes
Good notes on history and explanation of how/why they work “Optical mice use image sensors to image naturally occurring texture [on the surface they are placed]…. These surfaces, when lit at a grazing angle by a light emitting diode, cast distinct shadows that resemble a hilly terrain lit at sunset. Images of these surfaces are captured in continuous succession and compared with each other to determine how far the mouse has moved.” https://en.wikipedia.org/wiki/Computer_mouse https://en.wikipedia.org/wiki/Optical_mouse↩︎
note: this is very hypocritical coming from me. don’t mind my bad jokes!↩︎