Computer Input/Output Devices

An introduction to some of the more common input/output devices

Some computer devices are able to function as both input and output devices. This article will look at some of the more common devices and their uses.

MIDI-Enabled Devices

A MIDI (Musical Instrument Digital Interface) connection makes it possible to connect a range of musical instruments or devices, including electric keyboards, synthesizers, guitars and mixers, to a computer system. Often, computer sound cards will also include a built-in synthesizer as well, making it possible for them to produce MIDI sounds. It’s also possible to connect MIDI devices to each other, before connecting them to a computer system.

MIDI devices can be connected to a computer system through a variety of ports, depending upon the manufacturers design. MIDI to USB Interface, MIDI to Serial and MIDI to Firewire connections are the most commonly used and allow faster communication between the musical instrument and the computer or controller device.

An example MIDI Device
Multi-Function Printers

Multi-function printers combine both input and output features into one device and the vast majority of printers available on today’s market make use of these features. This enables users to save valuable office space. Typically, multi-function printers include some or all of the following features:

  • Printer (output)
  • Scanner (input)
  • Fax (both input and output)
Multi-Function Printer

A headset combines both headphones (audio output) and a microphone (audio input). Headsets can be used to take part in online meetings, online gaming with other players and to use with applications such as Skype.

KVM Switches

Keyboard, video & mouse (KVM) switches are devices that enable a user to control multiple computer systems with a single keyboard and mouse, each of which sending their display to a single monitor. This setup is particularly useful when managing test environments or accessing multiple servers that have no requirement for a dedicated set of input devices or display.

KVM switches mostly use USB or PS/2 connections and generally come in desktop, inline or rack mount versions. Some of the higher end rack mount KVM switches can be uplinked so that they can be connected to dozens of computer systems.

An 8-port KVM Switch
Touch Screens

Touch screens are perhaps one of the most common types of input/output device in today’s technological world, being used in mobile devices and laptops, point-of-sale terminals in fast food restaurants and some ATMs.

Touch screens are commonly controlled simply by the user touching the screen with their fingers, but there are some which make use of a stylus to perform the same tasks.

Touch screens are comprised of three ‘parts’ in order for them to function correctly:

  • Touch Sensors: The touch screen sensors are typically either a panel that lays over a standard display device or can be built into the monitor itself. In terms of the user, operation of both works in the same way.
  • A Controller: if the touch screen is using an overlay panel, the controller connects to the touch panel and then to the computer system port. Typically, these use a COM or USB port, although in certain circumstances the controller may connect to another port, device or drive. In the case of built in touch sensors, the controller is built into the monitor itself and the monitor carries two cables instead of the usual one which connects to the VGA or HDMI port on the system. The second cable attahed to the monitor will normally connect to the COM or USB port, although there are circumstances where it may connect to an alternative.
  • A Device Driver or Specialised Software: This enables the computers operating system to interpret the information sent to it by the touch screen device.
Smart TVs

Smart TVs are classed as hybrid devices. Smart TVs are television sets that have web and internet features built into it, accessible through the use of voice commands or via the remote control. In the vast majority of cases, there is no need to connect other devices to the television in order to perform the functions.

At first glance, this may appear to be a good use of such technology but some devices are not being continually updated as new features from content providers is made available. However, other manufacturers are continuing to provide updates for applications and firmware so that they continue to remain fully functional.

Another potential drawback for some smart TVs is that the voice commands do not have any security measures and are often sent to a third party. This means that there could be no protection for the information that you request. Some manufacturers and providers use the sent information to place additional advertising to your viewing experience. it’s important to consult the documentation that’s packaged with the TV in order to see what the manufacturers TV Privacy Policy is.

Set-Top Boxes

Set-Top Boxes take video content and then convert it into a format that can be viewed on a normal television. They are also known as streaming players or media players.

Traditionally, set-top boxes were utilised by cable television companies to descramble the broadcast signal so that only paying, authorised customers could view the offered television programs. Similarly, satellite television providers also have a set-top box that acts as a ‘descrambler’ for the information which allows over-the-air content to be viewed.

An example Set-top box

it’s also possible to purchase set-top boxes that are not specifically connected to a cable or satellite television provider. Such examples are Apple TV, Amazon Fire TV and Google TV. These devices differ in that they make use of WiFi or Ethernet connections to access the Internet so that content from providers such as Netflix or Hulu can be viewed. Some set-top boxes also include built-in Internet browsers.

In the vast majority of cases, these devices are connected to televisions through coaxial or HDMI connections.

Computer Audio Output Devices: Surround Sound

Computer Audio Output Devices: Setting up Surround Sound Sytems

A fair proportion of home audio systems are setup with some form of surround sound system. ordinarily, these setups are known as either 5.1 or 7.1 surround sound.

5.1 Surround Sound configuration contains one speaker at the front and center, a pair of speakers to the front side of the listener and another pair of speakers to the rear. 5.1 also has a subwoofer that can be placed anywhere in the room, although it’s commonly placed in front, somewhere near the front/center speaker.

A 5.1 Surround Sound Setup

7.1 Surround Sound configuration is very much the same as 5.1, with the exception that there is another set of speakers added to the sides of the listener, somewhere between the front and rear pairs.

A 7.1 Surround Sound Setup

Note: Professional entertainment centers, such as cinemas, often use systems up to and including 16.2 surround sound.

As with home entertainments systems, computer systems can also be connected to more than a single pair of speakers or set of headphones. Some computers even include all of the connections for a 5.1 or 7.1 surround sound system, depending on the included sound card.

Even if the computer doesn’t have the ports required to directly connect a surround sound system, there are a variety of ways that can be used to connect a computer so such a home audio system.

  • Analog Cable: in this method, the computer system is connected to the audio system through an analog cable, with a normal line out jack on one end and a set of RCA connectors on the other. Typically, the jack will connect to the line out or headphone port on the computer, whilst the RCA jacks are connected to a port on the audio receiver, most commonly the auxiliary ports
  • USB Cable: Computers can be connected to an audio receiver through use of a USB cable that has a normal USB connector on one end and a set of RCA plugs on the other. This allows both audio and visual data to be sent to the home audio system. Sometimes, an external digital-to-audio converter (DAC)is connected to the computer via a USB cable and to the home audio system using RCA cables.
  • Digital Audio Cables: Some computer systems come equipped with an S/PDIF port. This port can be used to connect a coaxial cable, with RCA connectors or a TOSLINK cable between the computer and home audio system. Other computer systems, including Mac computers, have a digital port in place of the standard headphone jack. These ports are able to transmit both analog and digital data, depending on which type of device is connected.
  • HDMI: If both the computer system and home audio system have HDMI ports, it’s possible to simply connect the two together through the use of a HDMI cable.

In the majority of cases when connecting a computer to a home audio system, it will be necessary to configure the setup through the computer systems Device Manager (or similar in non-Windows systems).

Security Input Devices

A look at a range of available security input devices

Security Input Devices

Assist in providing protection against unauthorised access to computing devices and associated resources. One of the most commonly implemented security input devices are biometric devices.

Biometrics are a method of recognising an individual based on certain physiological or behavioural characteristics. These characteristics are unique to the individual and include detection of things such as retina or voice patterns and fingerprints. Biometrics are fast becoming the foundation of secure personal verification solutions and secure identification. Some modern mobile phone technologies, such as the Sony Xperia range, are already including fingerprint biometrics into their operations.

Biometrics can also add an additional layer of physical security by verifying the identity of a person attempting to gain access to a system or device.

Due to their nature, biometric devices are more complicated to set up and will always require installation and configuration to the individual user before they are able to be used. The initial ‘object’ (e.g. fingerprint, retina scan voice print etc) that will be utilised by the system user will first have to be captured and stored. Once that has been completed, the user will then have to test the system in order to ensure that it accurately identifies and verifies them.

In the vast majority of cases, biometric devices are connected to a computer system through an available USB port.

Biometric Devices

There are a variety of different biometric security input devices available to support identification of an individual who wishes to use a computer system:

  • Fingerprint Scanner/Reader: These devices scan an individuals fingerprint(s) and match them to a database of stored prints in order to verify the person’s identity. Once verified, that person will be able to access whatever the scanner is protecting. If such a device is not already hardwired into a system (e.g. a building’s security system) then fingerprint scanners are typically connected to devices, such as personal computers, through a USB connection. Some laptops and mobile phones have fingerprint scanners built into them in order to improve the security of such devices.

    A Fingerprint Scanner
  • Retina Scanners: Work in a similar vein to fingerprint scanners by scanning an individuals retina pattern and comparing it to a stored database of scans to verify the user’s identity. As with fingerprint scanners, if the Retina Scanner is not hardwired into a system, it can be connected via a USB port. Very few personal devices currently have built in retina scanners.

    A Retinal Scanner
  • Voice Recognition: Make use of a spoken ‘pass phrase’ to compare against a stored database of voice prints in order to verify the identity of the person speaking the phrase. Similarly to both fingerprint and retina scanners, voice recognition devices can be connected to a computer system through a USB connection.
  • Signature Recognition: Makes use of a ‘signature pad’ on which an individual will physically ‘sign’ their name. This will then be compared to a database of stored signatures to verify the identity of the user. Other than the signature itself, signature readers also analyze other aspects of the signers behaviour, such as the strokes used and the amount of pressure applied to the pad whilst signing. As with all the other devices above, signature readers can be connected to a computer system through a USB connection if they are not already hard wired.

    A Signature Reader
  • Biometric Keyboards: Biomtetic Keyboards use a special program monitor the behavioural characteristics of a system user’s typing, such as key strokes, key press duration and pressure etc, in order to create a ‘baseline’ for the individual. Once this analysis is stored, the program will be able to challenge a user to verify their identity simply typing. The system will then compare this keystroke behaviour with that stored in the database for that particular user. Some biometric keyboards also have built in fingerprint scanners and the majority are connected to a system via a USB connection.

    Biometric Keyboard
  • Biometric Mice: A biometric mouse generally uses a form of biometric authentication before it will allow an individual to use a computer system. In most cases, this is typically a built in fingerprint reader which will then compare the offered fingerprint with those of that stored on a database.
  • Storage Devices: Biometric storage devices, ordinarily hard drives or flash drives, typically use a built in fingerprint reader to verify and allow an individual to access data stored on it. In most cases, these devices are connected to a computer system through a USB port.

    Biometric Flash Drive
  • Motion Sensors: Whilst motion sensors are not quite security input devices as we’ve looked at above, they do still classify as they are able to input a signal into a computer system when they detect changes in heat, normally caused by a human body. This is done through infrared sensors contained within the device. In most cases, motion sensors are hard wired into a security system and rarely connected through a peripheral connection such as USB.
  • Smart Card Readers: Smart card readers, unlike other devices looked at in this article, do not fall into the category of biometric devices. Smart card readers work through reading information stored within a microprocessor within a smart card. Ordinarily, this will provide a physical access token to provide access to a specific area for the user. Often, these smart cards take on the form of employee ID cards.

    Smart Card Reader

Multimedia & Optical Input Devices

Some of the more common multimedia and optical input devices

Multimedia Input Devices

Are devices which transfer sound, images, video or a combination therein to or from a computer system. Multimedia devices can be either input or output devices and common types of this device are digital cameras and sound devices.

Digital Cameras
Digital cameras capture and store photographic or video images through the use of electronic signals. The captured files are most often stored on removable memory cards, although they may sometimes be stored on embedded cards or optical discs.

It’s possible to transfer, print, save or otherwise work and edit with the information stored on the digital camera or removable memory by connecting the camera or storage media to a computer system.

If the camera has a removable storage media, it’s possible to transfer the data by connecting the card itself to the system through a media card reader.

The majority of digital cameras are connected to computer systems through USB or Firewire connections.

Camcorders & Video Recording Cameras
Video recording cameras work in very much the same way as other digital cameras. Often, data is stored on removable or optical media and the data is captured through analogue or digital electronic signals.

As with digital cameras, video recording cameras can often be connected to a computer system through a USB or Firewire port. However, some professional grade cameras may use tapes or disks that will need an alternate transfer method, sometimes additionally requiring digitisation.

A webcam, or Web Camera, is used to send a continual video feed or periodic images to a website for display. In the majority of cases, webcams capture the data in the form of JPEGs (images) or MPEGS (video) before uploading them to a web server.

Webcams are also used a lot within instant messaging software (such as Skype) and by some video applications. In some cases, companies and corporations might use webcams as a security measure.

As with digital cameras and camcorders, webcams are very often connected to computer systems through USB or Firewire ports.

A computer microphone allows audio data to be sent into a computer system. Normally this would be either for the data to be recorded or for use in ‘real time’, such as an audio feed that accompanies a webcam or video conference feed.

In the vast majority of cases, the microphone is connected to the computer system through a microphone jack or sound card. If the sound-card has colour coded ports, the microphone connection will be pink in colour. Otherwise, the ports will be marked with the word ‘mic’ or with a small microphone icon.

Most microphones have a 1/8-inch phono plug built into the cable to enable connection.


Optical Input Devices

Optical Input Devices offer a way for users to be able to transfer information from a paper, ‘hard-copy’ source into a digital format that the computer system is able to work with.

Scanners are used to take a photo-identical copy (scan) of a physical copy of any document (known as ‘hard-copy’) and create a digital format copy which can be stored, transfered or edited on a computer system.

A scanner works in a similar fashion to a photocopier but, ordinarily, has a much smaller footprint. Scanners can be attached directly to a computer system to import the scanned copies of documents. With the correct software, imported documents can be edited, manipulated for transmitted.

Typically, a scanner is connected to a computer system through a USB or High-Speed USB connection. In todays world, scanners are very often incorporated into multi-function printers.

Barcode Readers
Barcodes are able to provide a simple and inexpensive method of encoding textual information that can be easily read by electronic readers.

A bardcode reader scans a light source across the barcode and converts the pattern of reflected light into an electronic signal that is then decoded back into it’s original data format.

There are currently four styles of barcode reader available:

  • Pen-type readers (also known as barcode wands)
  • Laser scanners
  • Charge Coupled Device (CCD) readers
  • Camera-based readers

As with the majority of peripheral input devices, barcode scanners are connected to computer systems through USB connections.

Pointing Devices

A look at some common computer pointing devices

Pointing devices enable us to be able to navigate around the graphical user interface of a computer system easily, without having to be aware of the various command line prompts that would otherwise be needed in order to open and utilise applications.

Similar to most computer system peripheral devices, pointing devices come in a variety of designs.  The most common of these is the computer mouse, of which most of us will be familiar.  Other pointing devices include game pads, touch pads, track balls, joysticks, and graphics tablets.


The ‘mouse’ gets it’s name from it’s original appearance; that of a small rounded rectangle with a cable attached to one end. A mouse sends data to the graphical user interface (GUI) by having it’s movement tracked across the desk or mouse pad.

A typical wireless mouse with two buttons and a central ‘scroll wheel’

Most of today’s mice make use of optical technology to detect it’s movement through use of a laser. Unlike it’s ball-type predecessors, the lack of mechanical moving parts makes this mouse both more accurate and reliable.

Today’s wired mice are generally connected to a computer system through a USB port and, similarly, wireless mice connect to the system through a USB port transceiver. Alternatively, some mice make use of Bluetooth wireless technology to achieve the same goal.

The most common of today’s mice mice that come bundled with computer packages will typically have two main buttons and a central ‘scroll wheel’. However, there are a number of variations on this with some mice having up to 24 buttons available. This variation in buttons can be used for such things as moving forwards and backwards within browser windows or may be used to program functions for higher level PC gaming. Other mice, such as those that come with Mac computers have only a single button present.

Trackball Mouse

A Trackball Mouse is, to all intents and purposes, an upside-down version of a normal mouse. Instead of the later style of optical sensors, a trackball mouse has a ball just as the earlier versions of standard mouse had.

A Logitec Trackball Mouse

Signal are sent to a computer system from a trackball mouse by rolling it’s ball by movement of our fingers, thumbs or the palm of our hands. Similarly to a normal mouse, a trackball mouse will have at least one button to send signals to the computer system.

Touch Pad and Trackpoint

As the name might suggest a ‘touch pad’ is a small, touch-sensitive pad that is operated by the user running their finger across it’s surface. This is then converted into an electrical signal which is translated and transmitted to the system unit.

A Touchpad pointing device

Most touch pads have buttons just like their mouse or trackball counterparts. However there are also a high number of them which can be configured to detect the user tapping it’s surface with their finger, thereby processing that information in the same way it would as a click of the associated button.

Similar to Touch Pads are Trackpoints.  Trackpoints are normally found on laptops and are located either in the center or at the bottom of the system’s keyboard.  Ordinarily, Trackpoints are a small joystick style button that respond to directional force from the user in order to move the mouse pointer around the screen.

A Trackpoint device (above the letter ‘B’) with selection buttons underneath the spacebar

other Pointing Devices

In addition to the more traditional pointing devices above, there are other devices that have another primary function, but can also be used effectively as pointing devices.

Gamepads are primarily designed to be used within gaming applications. They are typically held and manipulated with two hands and feature a number of buttons that control different actions within the game or program.

The latest versions of many game pads also have sensors or pointing devices that can sense rotation, as well as direction of movement. A combination of these two are used to control actions within the game or application.

A Sony PS4, with it’s associated gamepad to the left

Most typically, gamepads connect to a computer system through a USB port although the most recent consoles and PC gaming pads use various forms of wireless technology to connect to the system unit.

A joystick is a stick or lever which pivots around a base and is used to control movement on a device. The majority of current joysticks also include a number of additional controls, buttons, toggles or switches to control other associated actions that the input is controlling. The joystick itself inputs the angle and direction of any desired movement.

A Microsoft joystick

At one time, joysticks were the most common input device to be used with gaming programs and applications. However, with the introduction and improvements with gamepads, they are generally used more within flight or space simulators. In addition, joysticks are also often used to control machinery such as cranes and unmanned vehicles (drones).

Once upon a time, legacy joysticks were connected to computer systems via a ‘game port’, a device port that was designed specifically for connecting this style of input device. However, most modern joysticks employ a wired USB connection to connect to the computer system.

Computer Keyboards – The Original Input Device

An overview of computer keyboard basics

Keyboards are possibly the original standard input device. In the very earliest personal computer systems as we’d recognise them today, prior to the introduction of pointing devices, they were the primary method of allowing the user to pass information and data into the system.

Keyboards ordinarily have a full range of dedicated keys including letters, numbers, and special characters. it’s also possible to use combinations of certain keys to create additional characters. Keyboards also contain a range of ‘special keys’ such as the Shift, Ctrl, Alt, Esc and Windows keys. Each of these keys can be combined with others to issue certain commands to the operating system or certain applications.

Despite having the same purpose and a similar form throughout, keyboards do have some variety. Some are designed with a bigger focus on ergonomics while others offer additional features (such as customisable hot keys, volume controls and scrolling). Many keyboards now connect to the computer system wirelessly rather than through a USB or other wired connection. Where a keyboard has a Bluetooth enabled connection, it can be used with both our mobile devices and computer systems.

Ordinarily, keyboards can be placed into one of three general categories:

  • Standard Keyboards have a varying number of keys and capabilities which is dependent on the manufacturer. Standard keyboards can be compact or regularly sized and may contain certain specialised keys (e.g. a gaming keyboard). Standard keyboards may also differ in other ways:
    • Being wired or wireless. Wireless keyboards typically use an adapter that connects through a USB port on the system unit. Others may use Bluetooth functionality that may or may not require an appropriate adapter. Wireless keyboards are often powered by AA or AAA type batteries, although some now are able to function with solar power.
    • Some keyboards might include specialised or programmable keys that are specifically aimed at engineers, graphic designers or gamers.
    • Some keyboards can include additional security features such as fingerprint scanners.
    • Some keyboards might include integrated pointing devices such as track pads.

    An example of a standard keyboard, including ‘hot keys’ and integrated pointing device
  • Ergonomic Keyboards usually have the key layout split into two halves, angled slightly away from each other, so that each hand can use it’s own set of keys.  Additionally, ergonomic keyboards tend to have built-in wrist rests and some may also include an integrated pointing device such as a track ball or touch pad.
Example of an ergonomic keyboard
  • Dvorak Keyboards have the keys rearranged into a more efficient layout which makes it possible for users who are familiar with it to be able to type faster.
The Dvorak Keyboard Layout

A Guide to CIT Troubleshooting

Taking a methodical approach to finding problems in a computer system.

It happens to almost anyone who uses computer systems at some time or another. Either a task that we’ve carried out many times before refuses to work, or a new piece of software flat refuses to load.

This article goes through the troubleshooting process, working it’s way towards finding a solution. It’s a general, theoretical, approach rather than an answer sheet, so there’s nothing mentioned that’s too specific.

I’ve attempted to keep this as generalised as I can so that it covers as wide a spectrum of potential troubleshooters as possible.  In the case where there’s a more professional slant to an aspect, that may not apply to those of us who are just attempting to sort out our home computer, the text will appear like this.

1. Identify The Problem
Before you can do anything constructive towards solving the problem, first we need to identify what the problem is. Ask questions about what was happening when the worst happened.

  • Were we able to complete the task earlier? If not, perhaps the answer is simply that the computer system’s hardware is not sufficient for the task
  • If the task was possible before, when did we notice the issue starting to develop? If we can work out what happened right before the problem appeared, it might be possible to identify the problem really quickly
  • What types of changes have there been since the last time that particular task was completed? If nothing is immedietly forthcoming, consider whether the computer system has been changed in any way since the last time the failing task was completed. Is there any new software? Have there been any updates to the OS? Has any new hardware been added? Again, this might well lead straight to the source of the issue.
  • Were there any error messages displayed? If we know what the error messages were, it might be possible to perform an internet search of the manufactures website or the internet in general for information

2. Establish a Theory
Quite simply, this is where we check everything that may seem too easy or obvious. Checking such things as that devices are actually plugged in and connected, that power switches are turned on and so-on. It’s important to make no assumptions about these obvious things as, quite often, problems are the result of the simplest things.

Having checked all of the above.

  • If it’s appropriate to do so, attempt to re-create the issue, paying close attention to what takes place and what the results are. If we’re experiencing a fault for the first time while focusing our attentions on the task at hand, rather than what’s going on around that task, we may have missed something vital.
  • If we’re assisting someone else, ask them to recreate the steps they took as exactly as possible. This way, it might be possible to identify an error in the way that they are using an application.
  • At this point, having done all of the above, it’s important to have a theory about what might have occurred. If our own experience falls short here, it might be time to refer to online forums and support websites out there. Whatever the problem is, I’d hazard a guess that others have had the same experience at some time and many will have asked for help online.

3. Test the Theory
At this point we’re now going to test our theory to see if we’re right; check and test related components, inspect connections, check any hardware or software configurations; consult the forums and online support as we mentioned above.

If we manage to confirm our theory but the problem is not yet solved, it’s time to decide what the next steps will be. On the other hand, if we haven’t been able to confirm our theory about what has gone wrong, we either have to look again and see if there’s an alternative theory or possibly consider that something is beyond our ability to fix, without additional resources of some kind.

4. Establish a Plan
Now it’s time for us to establish a plan of action about what we’re going to do to solve the problem. We may need to conduct further research, establish some new or alternative ideas and determine priorities.

We might even end up with more than one plan depending on what the potential causes of our problem are, so we’ll need to prioritize and execute each of these one-by-one.

It’s important to ensure that system downtime is limited and that productivity doesn’t suffer. A half day shutdown of a network, for example, when one machine has had a malware infection probably isn’t necessary and in truth, will likely only cause us more trouble than it will solve.

5. Verify
Once we have resolved the issue, it’s important to ensure that the entire system is functioning as it should be and, if applicable, implement some preventative measures. Preventative measures will include such things as updating system software and firmware or installing antivirus software.

We need to ensure that our solution has actually worked.  And that it hasn’t caused issues with other applications or devices connected to the system.

This part of the process may also include communicating or consulting with customers, colleagues or vendors to communicate the discovered issue, any solutions and any suggested preventative measures.  It might also be a good time to ensure that the customer/client is satisfied with the results.

6. Document
This part of the process very much depends on the nature of how we’re working with a computer system. Whatever the situation, it’s often important to document and share any knowledge gained from the work carried out.

For personal computer issues that we’ve sorted out at home, it may be worth a post in a forum or on a blog like this, if you have one. This is especially true if the cause was perhaps related to some form of malware or virus.

For computing professionals, this could take the form of our company’s documentation plans and for our own reference materials. Often, it’s a good idea to keep notes at each step of the process we’ve taken above while we’re carrying out the tasks.

This enables us to capture each valuable step of the troubleshooting routine, as well as the all important outcome for future use should a similar problem arise again.

Troubleshooting Display Devices

Some common display device problems and possible solutions.

Like all computer hardware, display devices can develop problems and faults. In this article we’re going to look at the more common problems and their possible solutions, starting with the easiest and most obvious.

Dark Screen
A dark screen or unlit power light may indicate that there is a fault to the power supply. This is somewhat fundamental and basic, but I know of more than one person who’s been caught out by it.

  • Check that the power cable is connected to both the display device and wall socket
  • Check that any connected surge protectors haven’t been tripped
  • Check that any circuit breakers haven’t been tripped – If power isn’t getting to any other local devices, then this is a likely cause.

Dim or no Image on Screen
Assuming that the power light of the display device is on, this could be due to an issue with data cables, improperly adjusted settings or the display being in power saving mode.

  • Press the power button to switch the device off, and then switch it on again (the famous “try and restart it” method).
  • Ensure that the data cable is correctly connected to both the display device and the input device.
  • Unless the display is particularly old, you should see an On Screen Display (OSD) message when power is present but no cable connected. In this case, a signal problem is most likely the issue.
  • If no OSD appears when a cable is disconnected then the display itself is likely faulty.
  • If an OSD does appear when the cable is disconnected and the device still fails to show any images, check the brightness and contrast settings. OSDs are not affected by these settings, so it would still appear.
A television OSD – In this example showing the channel and volume

Flickering or Distortion on CRT Devices
Flickering on a CRT (Cathode Ray Tube) type device is most often caused by a disruption to the signal being sent to the monitor.

  • Check the security of the connections between the device sending data to the display device and the device itself. It may need to be adjusted so that it is more securely connected to the video port, or there may be broken or bent pins. Attempt to straighten any bent pins and, in the even that any are broken, replace the cable itself.
  • An incorrect display adapter or adapter drivers may also cause this problem. If the POST (Power-on Self Test) is visible, but then the screen goes black once the system has started, it’s worth attempting to boot the device in VGA mode (‘VGA mode is a legacy mode with minimal video drivers and a screen resolution of only 640 x 480) and to verify that the correct adapter and drivers are being used.
  • The refresh rate may not be set correctly. The rate should normally be set as high as the adapter and device are able to support but, if set too high, it’s possible that this may have damaged the device.
  • Check the proximity to other devices of a similar nature. If a CRT display device is too close to another, then interference may become apparent. Continued interference of this nature may cause damage.
  • Check the colour depth settings on the display device. Incorrect settings may cause unusual effects on the display device.

The Display Switches Itself Off
This is normally caused by interruptions to the power supply of the display device from within the computer system itself.

  • Power Management Settings. These can be altered by going into the CMOS (Complimentary Metal Oxide Semiconductor) settings or in the display settings of the computer’s operating system.
  • The display’s video card is shutting down due to overheating. The only real solution here is to replace the video card or install additional cooling fans into the computer system.
An example CMOS/BIOS Screen

Application Problems
if a display device behaves in an erratic fashion, flickering or going blank from time to time when a specific application is running, it’s possible that the application requires an alternative resolution or colour depth. Right click on an area of the screen that doesn’t contain an application and select ‘screen resolution’ to change the settings.

Defective Pixels
Pixels that make up an LCD display device output will sometimes not display as they should. Generally speaking, there are two types of issues that pixels can fall foul to:

  • Dead Pixels are pixels that don’t display the output ligfht as expected. This is obvious when the LCD is displaying an image and there are black spots visible, containing no light.
  • Stuck Pixels are pixels that only show light so they are noticeable and out of place when the LCD is displaying an image. These lights can show as red, green or blue.

Repairing pixels that have become defective can be rather difficult to accomplish. In this case, the first port of call is to contact the manufacturer to check for warranty information. If the monitor is older and therefore out of warranty, it might be possible to fix the pixels by trying the following:

  • Use a blunt object to apply pressure to the screen in the area of the dead/stuck pixels.
  • Use heat, applied to the area of the defective pixels. In this case, we’re talking only about a hot, wet cloth that’s placed in a plastic bag and then applied to the defective area of the screen.
  • Use a defective pixel software utility. Such examples are: JScreen Fix, Dead Pixel Tester 3 and PixelRepairer.

Colour Issues
If the colour of a display device appears to be presenting incorrectly, the most likely cause is that the settings for the device are wrong. Simply adjust the settings to adjust the screen’s colours.

In the case of CRT displays, it’s possible that the device will need degaussing.

Physical Damage
This is something of a non-starter really. If there is visible physical damage to a display device, the most likely outcome is that it will need to be replaced. Cost and time considerations often mean that repair is not worthwhile.

Distorted Geometry
There are generally two causes for a display device to develop distorted geometry.

  • Running a monitor at a resolution that is not within it’s memory. This is easily fixed by using the standard monitor controls or adjusting the resolution via the computers operating system.
  • Magnetic interference. As mentioned in an earlier section of this post, attempt to move the device away from any possible causes of magentic interference. Again, over time, this form of interference is likely to cause damage over time.

Burn In
Image persistence (also known as ‘burn-in’) can happen with any type of display device. Burn-in is more prevalent on CRT and plasma displays than on LCD and is more likely to be prevented on LCD screens through the use of screensavers.

Oversized Images and/or Icons
Ordinarily, this is simply caused by the incorrect resolution being transmitted to the display device from the computer system. To correct, simply go into the display settings on the computer and adjust accordingly.

Video Card Issues
With video cards, there are some specific problems that can lead to, equally specific, symptoms.

  • If the computer will only boot into VGA mode, it’s very possible that the video card drivers are either missing or corrupted.
  • Visual anomalies or errors in the visual display of an image, known as ‘visual artifacts’
  • A Windows stop error, also known as the ‘Blue Screen Of Death’ or BSOD’ can be an indicator that there are issues with an installed graphics card.
  • Curves, waves, patterns or distortions in the video image.
NVidea GEForce 7800 Graphics Card

Here’s some additional troubleshooting steps to take in the event of video card issues:

  • Ensure that the graphics card is installed and seated correctly on the computer motherboard.
  • Ensure that the latest drivers for the installed graphics card and chipsets on the motherboard.
  • Check for any possible interference with other devices that are in close proximity. Try removing any devices that you suspect may be causing an issue.
  • Ensure the system is not being ‘overclocked’ beyond the capabilities of the installed graphics card.
  • Check physical items such as power cable connections and that all cooling fans are operating correctly.

Study Reference Disclaimer

Aspects of Display Device Configuration

The different variations about the configuration of display devices

Due to the high variation in the number of uses for computer systems, and their associated display devices, there is a common need to have to configure the devices to meet those uses.  This post looks at the various settings and features that may need to be considered when configuring a display device.

In the majority of cases, display devices can either be configured using buttons on the device itself or, in the case of computer systems, using a form of setting application within the computers OS.  One such example of this is the ‘Control Settings’ application on the Windows Operating System.

A dual, twin-monitor workstation.

The ‘resolution’ is the name used to describe the number of pixels that make up the dimensions of a computer display.  The value of the resolution is given as the number of horizontal pixels on the display by the number of vertical pixels (e.g. 1280 x 960).  In older displays, this was very often in the ratio of 4:3 (e.g. 1024 x 768).  In present day, widescreen display devices, including both computer display devices and televisions, have become much more popular.

Display device resolutions are significant because they represent how much information is able to be fitted onto a screen at the same time. For example, a widescreen display device with a resolution of 1920 x 1200 would be able to fit more than twice as much information, than a 4:3 ratio monitor with a resolution 800 x 600.
Table of various display device resolutions

Resolution # of Pixels Aspect Ratio
320 x 200 64,000 8:5
640 x 480 307,200 4:3
800 x 600 480,000 4:3
1024 x 768 786,432 4:3
1280 x 1024 1,310,720 5:4
1600 x 1200 1,920,000 4:3
1600 x 900 1,440,000 16:9
1920 x 1080 2,073.600 16:9
1680 x 1050 1,764,000 16:10
1920 x 1200 2,304,000 16:10

In 2015, information gathered from two surveys indicated that the current most popular display device resolutions are 1920 x 1080 and 1366 x 768.
✝ Information taken from Wikipedia

Native Resolution
Some LCD or other flat panel display devices can have a fixed resolution, otherwise known as a ‘native resolution’.  Devices which have a native resolution will only display a best quality image when the input signal is operating at the same native resolution of the display device.  A display device with a fixed resolution may display signal inputs at other resolutions, but this will always result in a loss of image quality.

Refresh Rate
Refers to the number of times per second that a CRT monitor is ‘refreshed’, meaning that the screen image is redrawn.  The rate of refresh is always described in hertz (Hz).  The most common value for refresh rate is 60 Hz, meaning that a screen with this value will get ‘redrawn’ sixty times every second.

It’s worth noting that these refresh rates are only applicable to CRT display devices and do not apply to LCD display devices.

The refresh rate may also be referred to as the ‘frame rate’, although this term is very often also applied to the rate at which software, such as games other resource heavy applications, are able to refresh their image on the screen.  In this latter example, the ideal ‘frame rate’ is still considered to be 60 Hz.

Brightness simply refers to the amount of light being emitted from the display device.  Measured in lumens, the standard unit of measurement for visible light emitting from a light source.  On practically every display device manufactured, it’s possible to increase or decrease the amount of light that is emitted.

If the brightness is set too high, it can cause an aura effect to be displayed on the screen.  If it’s set too low, it may make information difficult to read.  In either case, it’s important to consider how extended use of an incorrectly set monitor may affect a users eyesight.

Analogue Versus Digital
This is largely dependent on the make and type of the display device.  In the majority of cases, devices providing the input signals for a display device are inherently digital.  Display devices such as LCD or LED also innately support those digital input signals.

Privacy/antiglare filters
Privacy or antiglare filters are a physical accessory that can be attached onto a display device.  They can provide a number of benefits. For example;

  • Reduction of the glare from the screen (in relation to the user sitting in front of it)
  • Protecting the screen from scratches or dust
  • Prevents others, who are not sitting in front of the screen, from being able to view the information being displayed.  This can assist in enhancing privacy and protecting confidentiality.

Colour Depth Quality
Relates to the number of bits used to store the colour of a pixel.  The more bits that a pixel has, the more colours are able to be displayed.  It’s important to note that colour depth is only one aspect of the quality of the colours on a display device.  The other is gamut, but for the purposes of this information it’s not necessary to go into detail.

Table of various display device resolutions

Bit Depth # of Colours Scheme Name
1 bit 2 colours Monochrome
2 bits 4 colours
4 bits 16 colours
8 bits 256 colours Colour
8 bits 256 colours Grayscale
15 bits 32,758 colours High Colour
16 bits 65,536 colours High Colour
24/32 bits 16,777,216 colours True Colour
30/36/48 bits 1 billion + colours Deep Colour

For further information on colour depths, click here.

Contrast Ratio
The contrast ratio of a display device is defined as the difference, in luminance, of the ‘white’ brightness being divided by the ‘black’.  This figure is expressed as a ratio.

For example; a contrast ratio of 500:1 means that the ‘white’ areas of the screen are 500 times brighter than those of the ‘black’. A high contrast ratio is a desired aspect of any display device.

Multiple Displays
As technology has improved and computer systems have become more and more able to run a number of different software packages at the same time, many users have chosen to use more than one display device, in order to monitor or perform a number of concurrent tasks and increase the amount of display space.

Typically, a multiple display setup will include two display devices, although more than two devices can be configured with the appropriate expansion card(s) that are able to support such a setup.  Multiple displays like this are commonly used for professional computer workstations or for higher end gaming environments, where an extended desktop space is useful.

A multi-monitor gaming station, powered by the AMD Infinity

Within the display properties within a computer settings system, it’s possible to designate one of the monitors as the ‘Primary’.  This monitor typically displays the controls where all of the desktops administrative features can be called on (note: Since the release of Windows 10, these functions can be called upon from either monitor).  The second monitor would typically contain extra ‘workspace’, extending the available visible area to work in.

Whilst it would normally be the case in the situations described above to have the desktop span the different monitors and have alternative windows in each, it’s also possible to set the system up to duplicate the desktop image onto both windows.  This latter setup is useful to offer presentations.

Study Reference Disclaimer.

Display Device Connectors, Cables and Interfaces

A look at the wide range of display device connections and cables

There are a variety of connection types that are used to connect display devices to computer systems, although the majority that we are likely to come across are one of the following three types:

Video Graphics Array (VGA) is possibly the longest standing and most commonly seen display device connector.  It’s implemented with a 15 pin DB-15 high density connector that contains 3 rows of 5 pins. This type of connection is found on a great many computer systems, monitor devices and high definition television units.  In some instances, this type of connector may also be called a HD15 or DE15 connector.  On laptop computers and other small devices, a smaller ‘mini-VGA’ port is sometimes used instead of the normal, full size VGA connector.

    • Analogue or Digital: Analogue
    • Distance Limitations: 30 Metres for low resolution and 5 Metres for high resolution
    • Frequencies:  Needs a frequency of at least 6o Hz (which refreshes the screen 60 times a second, making the images appear constant to the naked eye).  In order for a full frame of pixels to fit 1/60th of a second, the speed at which each is transmitted needs to be adjusted.  This speed is known as the Pixel Clock.
A computer VGA Port

High Definition Multimedia Interface (HDMI) is an audio/video interface for transferring uncompressed video data and compressed or uncompressed digital audio data from a display controller to a compatible peripheral device.  Such devices include display monitors, video projectors, digital televisions or digital audio devices. A HDMI connector is made up of 19 pins and can support a multitude of modes such as; High Definition TV (HDTV), Standard Definition TV (SDTV) and Enhanced Digital TV (EDTV).  HDMI cables can run for up to 50 feet in length and the interface has largely superseded DVI.

    • Analogue or Digital:  Digital
    • Distance Limitations:  5 Metres
    • Frequencies: HDMI 2.0 (2013) supports resolutions of up to 4K (which is 4 times the clarity of 1080p) and up to 1356 kHz audio sampling frequency.  HDMI 2.0 also increased bandwidth to 18 Gbps.
    • HDMI Connectors:
      • Type A: 19-pin connector support all high definition (HD) modes and is electrically compatible with DVI-D Connectors.
      • Type B: 29 pin connector with double video bandwidth of the Type A connector to support very high resolutions (Not yet seen in any products and possibly superseded by Display Port (See below))
      • Type C: Mini HDMI connector which is used in portable devices
      • Type D: Micro HDMI which is the smallest version of HDMI connector and also used in portable devices.
Types of HDMI connection

Digital Video Interface (DVI) is able to transfer both analogue and digital video signals.  It’s common to find this connection type on many computer systems, DVD players, high-definition televisions and home theater systems.

DVI cables use a technology called Transmission Minimised Differential Signaling (TMDS) to transmit large amounts of digital data from the computer to a digital display such as a flat panel LCD monitor.
There are two different types of DVI connection: single-link and dual-link.  Single-link cables use a single TMDS link to carry information.  The single TMDS link has three data channels for RGB information and a maximum bandwidth of 165 MHz.  This can support display devices up to a resolution of 1920 x 1010 at 60 Hz.  DVI dual-link cables use two TMDS links at 330 MHz for each link.  Dual-link connections are able to support resolutions up to 2048 x1536.
A DVI-D Cable
      • Anaglogue or Digital: Dependent on the connector type (see below)
      • Distance limitations: 15 metres for low resolutions and 5 metres for high resolutions
      • Frequencies: In single-link mode the maximum pixel clock frequency is 165 MHz.  This supports a maximum resolution of 2.75 megapixels at a 60 Hz refresh.
      • DVI Connectors:
        • DVI-A: Analogue-only connection that requires a DVI-A supported interface and does not support dual link technology.  DVI-A is commonly used to connect VGA devices to a DVI-A port using a VGA/DVI-A adapter.
        • DVI-D:  Standing for ‘DVI-digital’ is a Digital-only connection. For a single link DVI-D, the connector has 18 pins, arranged in two groups of 9 pins each. To the side of the two groups of pins is another single flat pin, known as a ‘ground bar’.  This cable type is used with DVI-to-HDMI adapters.  A dual link DVI-D connector contains 24 pins, arranged into three horzontal rows of 8 pins.  As with the single DVI connector, it has a flat ‘ground bar’ located off to the side.
      • DVI-I: Also known as ‘DVI-integrated’ it’s capable of both analogue and digital connections.  In addition to the connections available on a DVI-D connector, the DVI-I connector has an additional 4 pins to carry any analogue signal.  In the case of single-link connections, the connector retains the 18 pin setup in the style of the DVI-D with 4 additional pins for the analogue signal.
The different DVI connectors

Other Video Interfaces

DisplayPort is a royalty-free digital display standard that aims to replace the DVI and VGA standards.  Unfortunately, DisplayPort is not backwards compatible with DVI or HDMI but, by using special dual-mode ports and adapters it may still be possible to use DVI and HDMI.

A DisplayPort connector

Similar to DVI and HDMI, DisplayPort uses TMDS link technology and it’s cables have 2-pin connectors.  Additionally, and in a similar vein to Peripheral Component Instrument Express (PCIe), DisplayPort is also able to support high-quality gaming or other applications that require high-end graphics.

A SlimPort (brand of Analogix) HDMI to DisplayPort adapter which complies with the Mobility DisplayPort (or MyDP) standard

Component video is an analogue video format that separates colour video signals into three or more channels.  Ordinarily, the three channel wires are identified as Y, Pb and Pr.  Y consists only of luminance and represents the brightness of the image.  Whereas Pr and Pb consist of red and blue, respectively, minus the luminance.  Sometimes component video can also refer to RGB signals and the three wire analogue RGB cable can often be used for high-end video cameras.

Component video cables

Composite video is simply an analogue video format that combines all of the video information into a single channel.  Composite video attempts to combine the information contained on analogue Component video channels and, consequently, does not provide a high level of quality. As technology continues to progress, composite video ports are becoming much rarer on devices.

A composite video cable and jack.

Radio Corporation of America (RCA) cables carry audio and video transmissions to a wide variety of different devices such as; televisions, digital cameras and gaming consoled.  RCA cables can also be used to carry digital audio, to send audio to loud speakers or even as a power cable.  RCA cable male connectors, and their female opposites on devices, are colour coded so as to provide a guide for users to know which cables to connect.  The most common RCA colours are; Yellow, for a variety of composite connections; Red, for the right audio channel connection and; White, for the left audio channel connection.

An example of RCA cables

Coaxial cable, also abbreviated to ‘coax’, is a cable that features a conducting central copper core, which is surrounded by an insulator and braided or foil shielding.  The included insulator keeps the copper core and the shield separate and the entire package is wrapped in another insulating layer, known as a ‘jacket’.   The data information is transmitted through the central conductor, while the outer shielding functions to reduce electromagnetic interference.

Coaxial cable and it’s parts: A – The outer jacket.  B – The shield. C – The insulating layer. D – The central copper core

Bayonet Neill-Concelman (BNC) connectors are used with coaxial cable in order to carry radio signals to and from devices.  BNC cables are commonly used to connect radio equipment and avionic components, although they are also able to carry video signals if required.  The actual BNC connections themselves come in two different versions.the 50 Ω and the 75 Ω.

The two different types of BNC connectors, showing both male and female versions.

MiniDIN-4 connectors are used with S-Video connections.  S-Video is a type of analogue video signal that carries video data as separate, brightness and colour, signals.  S-Video works in only two resolutions, 480i or 576i, and older versions of the system from the 1980s used different sized DIN connectors for various connections.

A miniDIN-4 S-Video connector

Video Adapters and Converters
Computers with built-in video cards and the associated monitors need to have a common connector type in order for them to connect and operate correctly.  Not every monitor has every type of connector and nor does every computer have every type of connector port.  It is possible to buy video graphics cards and add them to a computer system in order for it to be able to connect to a given display device, but it may be possible to achieve the same result more more cheaply by using a converter or adapter.

Adapters and converters can come in a variety of different styles, some simply a plastic housing with the different connectors at each end and others connected by a cable. Some of the more commonly found adapters include:

  • DVI to HDMI
  • DVI to VGA
  • Thunderbolt to DVI
  • HDMI to VGA

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