Power lines and interfacing in a computer

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Author: Atika M. Nyamoti

Power lines and interfacing in a computer 

An interface is a tool and concept that refers to a point of interaction between components, and is applicable at the level of both hardware and software. Most computer interfaces are bi-directional, but the mouse or graphics adapter are uni-directional.

kcse computer studies notes

Hardware Interfacing

-Hardware interfaces exist in computing systems between many of the components such as the various buses, storage devices, other I/O devices, etc. A hardware interface is described by the mechanical, electrical and logical signals at the interface and the protocol for sequencing them (sometimes called signaling)

  Peripheral devices interfacing

This refers to connecting a peripheral device to a computer through ports using either cables or wireless connectivity.
kcse computer studies
Ports at rare view

 Parallel Interface

Parallel cables transmit information simultaneously using a set of many conductors (wires). The advantage of using such cables is that they transmit data faster over a short distance.

A parallel cable connects to a parallel interface port commonly referred to as line printers (LPT). Parallel cables are used to connect printers, optical scanners and some removable storage devices such as a zip drive.
kcse computer studies notes
parallel cables

Serial interface

Serial ports also known as COM or RS232 ports, support transmission of data one bit at a time, hence it is slower than the parallel ports, However they are good than parallel cables because they can transmit data over a larger distance. They are used to connect devices such as the mouse and some printers.
kcse computer studies notes
serial cables


Is not an acronym unlike many of the other ports; it simply stands for the "com" in communications. It is commonly known as the serial port because it was the first port to use that type of communication. Widely used since personal PCs became a common tool. Are cheap and can be used with longer cables than parallel ports. Like the LPT port it is shaped like a trapezoid, but smaller, with the short end in the bottom and has 9 pins divided in 2 rows, one with 5 and other with 4 (be careful not to confuse it with the monitor port which is similar in size and shape but it has more pins and it is used only for monitors.) Commonly used to connect the mouse, keyboard, modems, cameras, and PDAs, especially before USB ports appeared. There are usually more than one COM ports in a computer and to differentiate them they are labeled with a number after COM. Commonly there are COM 1 and COM2 available. A typical COM port reaches speeds of 115Kb/sec.
Advantages-COM ports are very versatile. Many types of peripherals have used the COM port traditionally. Though, with the advent of USB, the use of COM ports is dwindling.

Common Peripherals-As mentioned above, COM ports are extremely versatile. They have be used to connect mice, keyboards, modems, cameras, and PDAs, to name a few.

USB-Universal Serial Bus

 is a serial and female port that can be use for any peripheral available in both Macs and PCs. It is one of the newest and faster computers available. It is slower than a FireWire port but is more than adequate for the type of peripherals for which it was designed for. In many ways have come to replace the standard parallel (LPT) and Serial (COM) ports, including printer, keyboard and mouse ports, having a much faster communication capabilities. Its speed goes upto 12 mbits/sec. The socket (and proper plug) in the computer has the shape of a thin a rectangle (called "Series A") measuring about 1/2 inch by 1/8 inch and are usually located on the back of your computer. Some computers also have USB ports located on their fronts (MAC in the side). When given a choice, it is suggested that the ports on the back be used so the ones in the front are available to plug a mobile device like a camera.

kcse computer studies notes
USB cables

Advantages: It has the capability of "hot plugging" which is the ability for plugging and unplugging a device without powering down. Now there are many motherboards that came with 2 USB ports available, being common in both Mac and PCs. USB devices are self-identifying, and USB is Plug-and-Play compliant, which means that installation and configuration of USB peripherals will be relatively easy. USB cables also carry power, so you don't need extra cables or transformers. · USB ports on your computer will work with any USB peripheral that you want to plug into it. USB is also "hot-swappable": you can plug stuff in or out without turning off the computer. One disadvantage is that is has to use a Windows98 or higher operative system and Windows NT doesn't support USB.

Common Peripherals: Even though USB supports any peripheral so far the most common ones that come with a connection for these ports are printers, digital cameras and mice.

Small Computer System Interface (SCSI)

SCSI stands for "Small Computer System Interface" and is usually known by the way it's pronounced "scuzzy". It's a general-purpose male and parallel port for connecting many different devices to a computer. It's a fast port that was available before USB and FireWire. Usually used with CD-ROM drives and scanners. Commonly present in older Macs, if you want to use it on a PC they require an additional card that rarely comes on a regular PC. A common SCSI port reaches between 5 and 10 mbits/sec. SCSI usually is more used in big computers like servers and mainframes. When it is used in desktop PCs it is because you can add a scanner and several other drives (CD, DVD or Zip drives) to one SCSI cable chain. However this is less important now that alternate multi purposes flexible ports such as USB and FireWire are more popular.
kcse computer studies notes
Advantages: SCSI ports are very fast and could in theory be used with any peripheral and with many of them at the same time. However really they are used mostly for scanners and external drives especially on Macs and big PC servers.

Disadvantages-One of the problems is that there is not a real standard for manufacturers so there are some different types of SCSI ports in the market. Also they are quiet expensive and so are the peripherals, cables and adapters associated with it. That is why they are more common in professional setting rather than for home use.

Common Peripherals: Even though theoretically they could be used with almost peripheral they are commonly used with scanners and external drives.

Personal System 2 (PS/2) Interfaces 

 PS2 is a port that was specially designed to use with mice and keyboards. It is also known as the standard mouse port. It's circular in shape about 1/2" and has six metal pins on the inside (Not to confuse with the old keyboard 5 pin bigger round connector.) This type of connection is common on all computers since 1997 and among other things it can serve to the purpose of freeing up a COM port to be used with other devices.

kcse computer studies notes
PS/2 Cable
Advantages -PS2 ports are always available in every computer. And it is fairly cheap compared to other ports. It is especially standardized for mice and keyboards.

Common Peripherals: Mice and Keyboards are commonly connected to computers by PS2 ports.

Audio Interface-Audio interface is used to connect speakers and microphone.

Fire wire Interface

FireWire is the newest and fastest serial computer port (bus) known also as i.Link (Sony) or IEEE-1394 by its technical name. It was developed by Apple and Texas Instruments mainly for use with video and audio demands in both Macs and PCs, but can be used for connecting many different peripherals. It reaches speeds of 400mbits/sec or even more in newer versions. FireWire is an Apple trademark but it has become the more commonly used name referring to IEEE-1394. It has 6 pins. The female or socket in the computer has a rectangular shape and the connector that goes on the peripheral is round. It has the capability of "hot plugging" which is the ability for plugging and unplugging a device without powering down. In many ways has come to replace SCSI as an external port. There are still only few motherboards that come with a FireWire port, being more common in Mac computers
kcse computer studies notes
Fire Wire Cable

Advantages FireWire transmits data very fast (400mbits/sec or more). FireWire is also capable of "hot plugging", which allows users to plug and unplug peripherals without restarting their computers.

Common Peripherals Currently FireWire is almost entirely used to connect digital video cameras to computers, though it is possible that many more audio and video media will utilize FireWire in the near future.


LPT (line print terminal or local printer terminal) is commonly known as the parallel port and typically used as the printer connection device. It can transmit signals for distances limited to 20 feet or less. It’s Faster than serial COM ports but more expensive. A typical LPT port reaches a speed of 150kb/sec. There can be more than one LPT ports in a computer and to differentiate them they are labeled with a number after LPT. It is most common to have only one for the printer called LPT1. It is shaped as a trapezoid with the short end in the bottom and 2 rows of pins, one 13 and other with 12 pins. 
kcse computer studies notes
Line Printer Terminal Cable
Advantages-It is faster than serial ports. It is available in every computer. Also, it is a port that is specially standardized for a printer to connect to a computer.

Common Peripherals-Commonly a printer uses LTP1 port.

Wireless peripheral interface

 A wireless peripheral interface is used for coupling with a Universal Serial Bus (USB) port for connecting a wireless peripheral with a host computer or controller. Wireless peripheral devices (e.g., keyboard, mouse, trackball, touch pad, joysticks, and game controllers) transmit communication signals, e.g., radio frequency (RF) signals, to the peripheral interface, which are received and processed into formats suitable for transmission to the host computer or controller via USB, either alone or in combination with other standard external bus systems, such as serial and PS/2. Other technologies for wireless interface include: Bluetooth, Wi-Fi (derived from playing with words I.e. from Hi-Fi which stands for high fidelity) and Infrared.

Infrared is a wireless interface that uses infrared to connect to infrared-enabled devices. Bluetooth is also a wireless interface that uses short-range radio broadcast to connect to any Bluetooth-enabled device. 
kcse computer studies notes
Wireless interface

Basic computer setup cabling

Before attempting to carry any setup activity, the following precautions should be observed:

1)      Disconnect all drives from power source before starting to work on them.

2)      Do not work on peripheral device without the guidance of a teacher.

3)      Never work alone because, you may need help incase of an emergency.

4)      Discharge any static electricity that might build upon the hands by touching an earthen metallic object and then wearing an antistatic wrist member. This is because your body can hold as much as 200 volts of static charge that can damage sensitive components on the mother board.

5)      Avoid touching metal conductors with wet hands. This may cause short circuiting thus damaging chipsets.

6)      Don’t force a component to open/eject. There are laid procedures for every opening/ejection. Force can break or destroy a component makeup.

Tools and other requirements

The following tools are necessary in any setup:

  1. Screw drivers
  2. Antistatic wrist member
  3. Pliers
  4. Devices manual
  5. Devices software (drivers)
  6. Fuse testers
  7. Gloves etc

Mounting internal devices

External devices are connected to the motherboard via special sockets known as ports whilst internal devices are connected through slots and sockets. It’s recommended to study the manufacturer’s manual before connecting devices.

Mounting hard drives and optical drives

Internal devices are connected to the motherboard using special ribbon cables. Hard disks and optical drives are connected to the motherboard through interface connectors commonly referred to as controllers. Three types of controllers are:

  • Ø  EIDE- enhanced Integrated Drive Electronics
  • Ø  SCSI-  Small Computer Systems Interface
  • Ø  SATA- Serial Advanced Technology Attachment

EIDE are more efficient and supports hot-swapping. Hot-swapping means that a drive can be removed or inserted while the computer is still on. Each EIDE supports up to two drives on a single ribbon cable. This type of setup is called a master/slave configuration because one controller directs the activities of both drives. To mount an EIDE drive, proceed as follows:

  1. Wear antistatic wrist member to discharge any static charge on the body.
  2. Determine which drive will be the master and use the drive label information to determine which jumper settings to use for a master or a slave.
  3. Check that a free drive bay is available, slide the disk into that bay and screw it into place.
  4. Ensure that there is free power connector from the power supply unit and connect it to the drive. Notice that it is designed to fit in its socket in only one direction.
  5. Identify pin 1 as labeled on the drives socket and match it with the red or brown continuous line of the ribbon cable. Most cables will only fit in one direction.
  6. Connect the interface cable to the drive, then into the controller slot on the motherboard.
  7. If installation is complete, replace the casing power. 

Connecting external devices

To connect a device to the system unit, you need to identify its port and interface cable.

  1. Gently and carefully connect the interface cable of each device to the correct port and to the device if it is not already fixed permanently.
  2. Connect the computer to the power source and switch it on.
  3. Observe boot up information on the screen to see whether Power-On-Self-Test (POST) displays any error message.
  4. A successful boot means that the computer was properly set up

Group Discussion for Revision questions on topics

  1. What are:
    1. input devices
    2. processing devices
    3. output devices
  2. Discuss the following terms

a.       data

b.      information

  1. Name four main parts that make up a computer
  2. What are peripheral devices?
  3. Name such devices in question 4 above
  4. With the aid of an organizational chart, show how computers are classified.
  5. In which classification do the school computers belong? Why?
  6. Discuss classification of computers according to:

a.       Size

b.      Purpose

c.       Functionality

  1. With an aid of a diagram show how digital and analogue signals are represented.
  2. Name at least six microcomputers available in the Kenyan market today.
  3. Name 10 areas where computers are used and what they are they used for?
  4. What are the main functions of a computer?
  5. What is the main purpose of a computer?
  6. Briefly discuss evolution of computers since ages before Christ to date?
  7. Discuss causes of computer damage in the computer lab and how to avoid them?
  8. List six safety precautions in the computer lab. Why are they necessary?
  9. Discuss classification of keyboard keys and give examples for each classification.
  10. Draw symbols for each keyboard key listed below and indicate their uses?

a.       SysRq

b.      Escape key

c.       Spacebar

d.      Backspace

e.       Home

f.       End

g.      Insert

h.      Tab Key

i.        Shift key

j.        Control

k.      Num Lock

l.        Caps Lock

m.    Scroll Lock

n.      Windows logo key

o.      Menu Key

  1. Indicate whether the following devices listed below are pointing, scanning or keying devices.

a.       Joy Stick

b.      Keypad

c.       Flatbed

d.      MICR

e.      Keyboard

f.       Mouse

g.      Trackball

h.      OBR

i.        OCR

j.        Stylus

k.      Light pen

l.        Touch screen

m.    Camera

  1. …………………is regarded as the brain of the computer and also known as a microprocessor.
  2. Using an organizational chart, show parts of the Microprocessor.
  3. ………………..is used to input voice in the computer.
  4. By the use of a well labeled diagram, show all the events that ‘task A’ go through to be processed into information.
  5. This is a gadget mounted on the motherboard, drives or HDD used as a ROM, hosts a number of other electrical gadgets like capacitors, resisters and transistors. Even the microprocessor belongs to this gadget. What is this gadget?
  6. Kwamboka went into a shop to buy a RAM for her desktop computer and she encountered problems in interpreting the following abbreviations: DDR, SDR, DIMM, SIMM, SRAM and DRAM. Can you help her understand these terms?
  7. Differentiate between a computer, a system and a computer system.
  8. The speed of a computer is measured by the frequency of computers processing signals. True/false? If true, explain how?
  9. Draw a well labeled diagram for:

a.       HDD

b.      HDD-disk platter

  1. Name six softcopy display devices available in the Kenyan market today. How do they differ from each other?
  2. Discuss:

a.       Pixel

b.      Color depth

c.       Resolution

d.      Refresh rate

e.       Display size

  1.  By the use of organizational chart, discuss classification of printers.
  2. ……………… is a special type of printer used to produce bill boards, engineering drawings, maps etc
  3. Discuss:

a.       RAM vs. ROM

b.      Firewire vs. USB

c.       PS/2 vs. Wireless

d.      SCSI vs. Firewire

e.       COM vs. LPT

  1. Disconnect all computer parts and reassemble them again. Write a report on every activity observed. The report should feature:

a.       Tools used

b.      Safety precautions observed

c.       Disconnecting procedure

d.      Procedure for connecting the CPU, HDD, Drives, Cards, CMOS battery, peripheral devices and  which interface was used to connect which device

e.       A successful booting procedure.

  1. Discuss numerous factors to consider when purchasing a printer.
  2. Nyambura bought a brand new desktop computer with a warranty but upon reaching home, the computer could not boot. List numerous reasons that may have caused the computer not to boot. What will you advice her to do if the computer failed completely to start?
  3. discuss:

a.       Wi-FI vs. Bluetooth

b.      Keypad vs. Keyboard

c.       SMS vs. MMS

d.      Memory Card vs. Flash Disk

e.       CD vs. LS Super Disk

f.       Optical Tape vs. Optical Card

g.      Gramophone Disk vs. DVD

h.      Live disk vs. HDD

  1. Discuss and analyze all video adaptors
  2. what are these devices used for:

a.       LED

b.      Speakers

  1. What are the advantages of tower computers over desktop computer models
  2. Give reasons who mobile phones are regarded as computers
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