CIS 107a: Introduction to Hardware Concepts

Chapter 8: Installing and Supporting I/O Devices



This chapter covers several topics, grouped under the heading of Input and Output. The objectives important to this chapter are:

  1. How to install a new device on a computer
  2. About keyboards, pointing devices, and video subsystems
  3. About ports and expansion slots for I/O devices
  4. Troubleshooting I/O device problems

The text points out that you usually install a device first, then install a driver. Most of the time you allow Windows to notice a new device, and allow it to offer a driver for it. However, sometimes the correct procedure is to install a device driver first, which you cannot know unless you read the instructions for installation of the device. This will be a foreign concept to many of you, I am sure. Trust me, there is something to be gained by reading the instructions first.

Keyboards are discussed first. Keyboards commonly connect to a computer by one of three kinds of plugs (two are illustrated on page 312):

If a keyboard has one kind of connector, and the computer in question has another, it is not unusual to use an adapter. (This link will take you to where you can search for many kinds of adapters.)

The main trouble with keyboards is that they stop working, usually after being mistreated. Keyboards are often considered consumable items, and are simply replaced rather than repaired.

Pointing devices come in a variety of shapes and styles. Page 314 shows photos of a mouse, a trackball, and a touch pad. Each device has its own virtues and its own problems.

  • Mice and trackballs both collect dirt, and the balls need to be cleaned periodically. In addition, the rollers that the rubber ball rolls against need periodic cleaning.
  • Trackballs also collect oil from human skin, creating another need for cleaning.
  • Touch pads should be used carefully. A touch pad has a finite surface: if you are dragging an object and you reach the edge of your touch pad, you have to remove your finger from the touch pad, and replace your finger in another place. Some touch pads can interpret this action as a click. Mice do not have this problem.
  • Optical mice do not use a ball technology, so the problems with dirt and oil are much less. They use a sensor that notices changes in the area under the mouse when it is moved. A good mouse pad can enhance the performance of this sort of mouse.
  • Another pointing device made famous on the IBM Thinkpad notebooks is called a TrackPoint. It looks like a small joy stick, and is actually a small round button in the middle of the keyboard that is mounted on a stress gauge. The mouse pointer moves when the operator presses against the button in any direction. This seems to be less popular with users who have wide fingers.

Some computers have dedicated mouse ports. This can accept a trackball just as well as a mouse. Either device might connect to the computer by a serial port, a PS/2 port, a USB port, a port on the keyboard, or a wireless adapter.

Some tablet computers allow you to enter data on the screen, making the monitor an input and output device. Such screens are also found on kiosks in many malls, eliminating the need for a keyboard.

Monitors and video cards are the last topics in the chapter. Monitors may be considered as falling into two categories: CRTs and flat panels.

A CRT is a Cathode Ray Tube. (A cathode is a negative electrode. It produces electrons.) This is a monitor that looks a lot like a television set. Images are produced in monochrome (one color) or composite color. Color monitors typically create images by combining red, green, and blue picture elements (pixels) to create a range of colors.

Some feature of monitors are listed. They affect the usability of the monitor.

  • screen size - the diagonal size of the picture tube. Actual usable picture size is usually about an inch smaller for tube type monitors, while the advertised size for a flat panel is usually true to the viewable size.
  • refresh rate - how many times a second does the monitor "paint" a new picture. More is better. Users may be irritated by flickering if a monitor has a refresh rate below 70 Hz.
  • interlacing - an interlaced monitor will alternate drawing even and odd horizontal lines on its screen. A non-interlaced monitor draws all lines from top to bottom with each pass. Non-interlaced is considered easier to watch.
  • dot pitch - distance from the middle of one pixel to the middle of the next pixel. Smaller is better. Monitors with a dot pitch larger than .28 mm are not considered good. Footnote: This is only true for monitors that use a shadow mask display method. Some monitors (such as Trinitrons) use a different method, called an aperture grill. Such monitors do not truly have dots, so this measurement is not accurate for them. See the explanation at
  • resolution - the number of vertical and horizontal lines that the monitor can display. A common resolution for Windows users is 800 columns by 600 horizontal lines. Remember that you may be able to increase the resolution on a monitor, but each time you do, the items displayed on the screen will appear smaller. As noted below, greater resolutions require greater amounts of video RAM.
  • multiscan - a multiscan monitor is one that can be adjusted to any of several refresh rates.
  • "green" compliance - environmental standards established by the U.S. Environmental Protection Agency are represented by the EPA Energy Star program. Monitors that comply with these standards save on electricity and emit less heat than non-compliant monitors.

Flat panel monitors are found on portable computers and, more recently, as an alternative to CRTs for desktop computers. They take less space than a CRT and typically cost more than a CRT of the same size. Flat panels come in two basic varieties: active matrix and passive matrix. Active matrix screens cost more because they have more transistors to amplify and brighten the picture. Passive matrix screens do not have this feature, so they are often dimmer. If something goes wrong with one of these screens, the average technician will not be able to do much but swap it out for a new one.

A popular option for many users is to install two monitors that act as one larger monitor, giving the user an extended desktop. In order to do this, the user must obviously have two monitors, and must also have either two video cards, or a single card that supports connecting two monitors. It is usually possible to give each monitor with different settings, if this is helpful for the user.

Video cards are called by several names, listed in your text. The text also lists four kinds of video output that might be offered on your card:

  • RGB output - this sends red, green, and blue signals to the monitor, usually through a VGA port. VGA ports have 15 pins, and are often blue.
  • DVI (Digital Visual Interface) - this kind of port is for passing a digital video signal directly to a digital monitor. If your video card has a VGA port and a DVI port, and you have two VGA monitors, you can use an adapter to connect one monitor to the DVI port.
  • Composite video - this method combines the red, green, and blue signals into one signal that is passed through an RCA connector
  • S-Video - a super video connector is commonly available on video recorders, video players, and larger televisions. Output from this port provides a better signal than composite video, but not as good as VGA or DVI. It does, however, allow connection to television equipment instead of monitors.
  • HDMI (High-Definition Multimedia Interface) - may replace DVI, used to connect the video card to high end televisions or home theaters. It is possible to connect a DVI port to an HDMI jack with an adaptor cable.

Video cards typically use the the PCI or AGP bus on the motherboard. AGP cards are available in several varieties, that have only become more confusing to the consumer. As is often the case, the article on Wikipedia about AGP is very helpful. Another helpful page is found on the Matrox graphics card site. An AGP slot may appear as one of six styles.
Slot description Slot type
short, voltage key toward rear of computer 3.3 Volt AGP 1 or AGP 2 slot
short, voltage key toward front of computer 1.5 Volt AGP 1 or AGP 2 slot
short, no voltage key 3.3 or 1.5 AGP Universal slot
long, voltage key toward rear of computer 3.3 Volt AGP Pro slot
long, voltage key toward front of computer 1.5 Volt AGP Pro slot
long, no voltage key 3.3 or 1.5 Volt AGP Pro Universal slot

The author notes are three AGP standards (1.0, 2.0, and 3.0) that apply to the table above, and four AGP speeds (AGP 1x, 2x, 4x, and 8x). The speeds each run the indicated number of times faster than the standard AGP card.

Installations fall into two general types: you install something internally, or you attach something to an available port. It is common to have the most of the ports listed in the text on most computers. A current model may have serial and parallel ports, and some version of USB ports. Some computers will have one or two IEEE 1394 ports. It is noteworthy that some manufacturers stopped providing serial and parallel ports on their computers in late 2004, or early 2005.

As time goes by, the available speeds of IEEE 1394 and USB ports and devices will continue to change. For this course, be aware of the speeds noted in the text:

  • IEEE1394b - 1.2 Gbps, 800 Gbps (few devices available at this rate)
  • USB 2.0, Hi-Speed - 480 Mbps
  • IEEE1394a - 400 Mbps
  • USB 1.1 - 12 Mbps
  • Parallel - 1.5 Mbps
  • Serial - 115.2 Kbps

The text discusses:

  • serial ports - often called COM ports. Think of the serial port as the physical aspect of it, and the COM port as the logical label for it.

    Serial Port IRQ Memory Address
    COM1 IRQ 4 03F8h
    COM2 IRQ 3 02F8h
    COM3 IRQ 4 03E8h
    COM4 IRQ 3 02E8h

    You should know that COM1 and COM3 share IRQ 4, and that COM2 and COM4 share IRQ 3. In the memory addresses, the small h is to tell you that these are hexadecimal numbers. Serial ports commonly have 9 or 25 pins. Only nine of the pins are used, even if it is a 25 pin port.
    Sometimes computers are connected together with a null modem cable connect to their serial ports. The following link will connect you with a site that shows a wiring diagram for such a cable, using either DB-9 or DB-25 connectors. This provides a fast channel between the two computers that avoids the need for other hardware.
    Data bits are sent serially on serial ports, one bit at a time.
    Serial ports are controlled by UART (Universal Asynchronous Receiver Transmitter) chips, which have gone through several design changes. Main idea: the latest chip may be required to support the latest equipment.
  • Infrared transceivers - Some devices have IrDA (Infrared Data Association) ports to communicate with computers or other devices. For example, Palm PDAs typically have infrared ports that can be used to copy information from one to another. Some computers use wireless keyboards or mice that communicate via infrared. Such devices commonly use COM4 as their logical port, but an infrared printer will often use LPT3. An infrared receiver may be plugged into your second serial port (COM2), and logically assigned to COM4. Infrared devices are typically short range, line of sight devices.
  • parallel ports - commonly called LPT ports, which is a logical label, not a physical label. Many computers only have one. LPT 1 may be assigned to IRQ 7, address 0378h. Since computers often do not have a second parallel port, the IRQ for LPT 2 (IRQ 5) may be available for another device.
    Data are sent eight bits at a time on parallel ports. Shorter data cables are recommended, since no standard for the length of a parallel cable was ever established.
    Parallel ports come in three types: standard, enhanced parallel port (EPP) and extended capabilities port (ECP). ECP requires assignment of a DMA channel, usually 1 or 3.
    The standard port is meant to be unidirectional, the others are bi-directional. Parallel ports often have 25 pins on the PC, but the connector on a printer may be proprietary. A common interface on a printer is the 36 pin Centronics connector, or the newer 36 pin Mini-Centronics (Micro-Centronics) connector.
  • USB ports - USB ports use an IRQ, an I/O address, and a DMA channel. The good news is that those same three resources are shared by all USB devices on your system. Note that Windows NT and 95a do not support USB ports, even if the hardware is installed on the computer. Windows 98SE supports storage devices, but not printers or scanners. Windows 2000 and XP have little trouble supporting these devices.
    USB has had version upgrades. USB 1.1 supports data transfer at up to 12 Mbps. USB 2.0 supports up to 480 Mbps.
    A USB cable has four wires: two for data, one for ground, and one for power. USB cables often come with two types of connectors. The A connector is rectangular, the B connector is more like a small square with a rounded top. Other plug designs are used as well.
  • IEEE 1394 ports - can have four or six wires. Four wire connectors only pass data, while six wire connectors have power and ground wires as well. Data is passed over two pairs of STP (Shielded Twisted Pair) wires. IEEE 1394 can use isochronous data transfer, which uses a separate timing device, allowing the data stream to pass without including timing signals in it.
    Current line speeds vary: 100, 200, and 400 Mbps (IEEE 1394a). As noted above, IEEE 1394b can support 1.2 Gbps, and is expected to support up to 3.2 Gbps transfer.

To see some nice diagrams follow these links to resources on the BlackBox site:

  • Data interfaces - shows the number of pins, connector shape, and wiring for several connector types
  • Connector Guide - an identification chart for several types of connectors

To examine what resources are currently in use (or available) it is suggested that you use Device Manager for Windows machines.

Sometimes, drivers are not recognized by a system. In Device Manager, these are identified by exclamation points in yellow circles beside the names of the devices with problems. For a discussion of this feature, search the Microsoft Support site for information on Device Manager.

Adding a PCI card to a computer should be easy. The PCI controller is meant to take care of resource assignment. PCI devices can share one IRQ if you enable PCI bus IRQ steering. This is not possible if the BIOS and the OS do not both support the option. In some cases, you can resolve a problem by turning this feature on, and in other cases, you resolve the different problems by turning the feature off. It can be accessed in Windows by finding the PCI bus object in Device Manager, then clicking the Properties button for that object.

A basic set of steps for resolving resource conflicts is presented:

  1. Determine which IRQs are in use, and which are available
  2. Determine which I/O addresses are in use
  3. Determine what upper memory addresses are in use
  4. If a conflict is with an ISA device, change jumpers or DIP switches to select another resource (this must be a valid resource for the device)
  5. If the device is limited to only one IRQ, reserve it in CMOS for the device, then let Windows allocate resources to other devices
  6. If PCI bus IRQ steering is supported but not enabled, enable it. (Or turn it off, if enabled.)
  7. Use PCI bus IRQ steering to force a device to use a different IRQ.
  8. If the problem is with a PCI device, move it to a different slot, to force a resource reassignment.

A section on troubleshooting concludes the chapter. It is very detailed, and students should read through this section especially carefully.