Loading presentation...

Present Remotely

Send the link below via email or IM


Present to your audience

Start remote presentation

  • Invited audience members will follow you as you navigate and present
  • People invited to a presentation do not need a Prezi account
  • This link expires 10 minutes after you close the presentation
  • A maximum of 30 users can follow your presentation
  • Learn more about this feature in our knowledge base article

Do you really want to delete this prezi?

Neither you, nor the coeditors you shared it with will be able to recover it again.



No description

Ferran Palau Luján

on 8 September 2014

Comments (0)

Please log in to add your comment.

Report abuse


Types and Components of Computer Systems

Output Devices
As the name suggests, output devices are hardware devices that allow data to be output from a computer. Some devices hold the data temporarily (such as a printer) whereas other devices produce permanent output in the form of a hard copy.
stands for
which is the system it uses so you are able to see the screen. They are the cheapest type of monitor as the LCD monitors are taking over.
CRT monitors are used as the primary output device for computers so the user can see immediately what they are typing in.
They are used with light pens, for example to allow designs to be created on screen.
CRT monitors still produce a higher quality image than LCD monitors.
The angle of viewing is still better than with a LCD monitor.
They work with light pens in computer-aided design and computer-aided manufacturing (CAD/CAM) applications.
LCD monitors are used as the primary output device for computers so the user can see immediately what they are typing in.
They are an integral part of laptop computers.
Its is heavy and boxy and occupies a lot of space.
They are not sold in different sizes.
Overheating can cause fires (especially as they get older)
Overuse for a long period of time can cause headaches and damage your eyesight.
stands for
LCD monitors are taking over CRT monitors as the main output device. One of the reasons for the rapid development of laptop computers can be attributed to the advancements made in LCD technology.
LCD monitors are lightweight, so do not pose the same risks as CRT monitors.
produce less glare, emits less radiation and consumes less power than CRT monitors.
Don't overheat as much as CRT monitors.
Not as good definition as CRT monitors
Cannot be used yet with light pens.
When looked from the side, image becomes unclear.
Still quite expensive.
PDP stands for Plasma-Display-Pannel. A plasma display panel is a type of flat panel display common to large TV displays 30 inches (76 cm) or larger.
Can be used for either TV or computer.
Larger screen size availability.
Better contrast ratio and ability to render deeper blacks.
Better color accuracy and saturation.
Better motion tracking (little or no motion lag in fast moving images).
Plasma TVs are more susceptible to “burn in” or “screen burn” of static images.
Plasma TVs requires more power thus more heat produced than LCDs.
Does not perform as well at higher altitudes.
Shorter display life span than LCD. This can vary according to other environmental and use factors.
PDP Monitors
stands for
Surface conduction-Electron emitter-Display
. It is a display technology which has been developing various flat panel displays by a number of companies as electronic visual displays. SEDs use nanoscopic-scale electron emitters to energize colored phosphors and produce an image onto a screen.
As they are still designing them there are no confirmed uses but they could be used as portable computers or televisions.

CRT-matching black levels.
Excellent color and contrast potential.
Relatively inexpensive production cost.
Wide viewing angle.

Unknown (though optimistic) life expectancy.
Potential for screen burn-in.
Currently prototype only.
Will be really expensive in their complete form.

Laser printers produce very high-quality hard copy output. The print rate per page is very if a large number of pages are being printed.
Laser printers are used where noise levels need to be kept low (like in an office).
Best option for fast, high quality volume printing.
They can handle very large printjobs
Consistently high quality
Fast when printing large quantities
Toner cartridges last for a long time
Cheap to run
Laser printers are expensive to buy
They are only really fast if several copies are being made
Colour laser printers are more expensive to run as they need four different cartridges as well as diffuser kits and other devices
Can cause diseases as they produce ozone and volatile organic compounds.
Inkjet printers are used to produce good quality hard copies. Unlike laser printers, inkjet printers do not have large buffers, so printing is done a bit at a time
nkjet printers are used where low output volumes are requiered
If high quality printing is required for single pages this printer is ideal, for example, it prints photos in a very high quality
The output is of high quality
Inkjet printers are cheaper to buy than laser printers
They are very lightweight and take little space
They do not produce ozone and volatile organic compounds, unlike laser printers
The output is slow if several copies needed, as there is little buffer capacity to store the pages
Ink cartridges run out very quickly
Printing can "smudge" if the user is not careful
Expensive to run if used a lot
These are a new type of printer that produce solid 3D models using modified inkjet technology. In this technology known as "tomography", thin layers of fine powder (plaster, resin and starch) are bonded together as a 3D model is slowly built up.
Inkjet printers are used to produce prototypes which actually work from CAD packages, photograph image, stored drawings, etc.
Scale models are produced in colour before the real thing is manufactured
The ultimate objective is to produce organic objects using layering technology.
3D inkjet printers save a lot of money, since making prototypes by other methods is very expensive
The powders can be re-used
Physical scale models are produced with working parts
3D inkjet printers are very expensive to buy
They are slow at producing their output
The end product can sometimes be a little rough

Plotters are devices that produce hard copies, but operate in a different way to printers. They are not limited to normal printer paper size and are capable of producing highly accurate, very large drawings and posters. The most common ones are pen plotters.
They can produce huge printouts
The print quality is extremely high
They are slow in operation
They are expensive, both to buy and to maintain and to run
Plotters are used to produce large drawings (for example blueprints of buildings) and are often used with CAD applications.
They can also print on plastic-coated paper
Pens can be replaced with other tools
Speakers can be connected directly to a computer or are built into the monitor or casing (as in a laptop computer). Digital data from the computer is converted into analogue form, using a digital to analogue converter (DAC). The signal then amplified through the speakers.
Speakers are used to output sound from multimedia presentations.
They are used in home entertainment centers.
Can help blind people buy narrating text in the computer
They are used to play sound in downloaded files.
Good sound reproduction
Very reliable
If treated properly can last a long period of time
Wide variety of speakers in the market

Limited in frequency response
Need multiple speakers to produce full sound spectrum of 20 - 20,000 Hz
Cheap speakers are quite bad and tend to last a short period of time.
Good speakers tend to be quite expensive
Multimedia projectors receive signals that can be either analogue or digital, although most modern projectors only work with digitalinputs.The image from the source (usually a DVD) is magnified onto a scrren. These devices usually work with a remote control.
Multimedia projectors are used for training presentations (to allow the whole audience to see the images from a computer)
They are also used for advertising presentations (large image showing product features of, for example, a new car, can be shown at exhibitions, shopping malls.etc)
Home cinema systems use multimedia projectors.
They enable many people to see a presentation rather than all of them crowding round a small computer screen.
They avoid the need for several networked computers logging at the same time on to a number of computers.
Images can sometimes be fuzzy
Multimedia projectors are expensive to buy
Setting up projectors can be a little difficult
Control devices are another type of output device. They are used to control processes in conjunction with sensor input devices.
The buzzers are switched on or off by the actuator
Buzzers are used in cookers and microwave ovens to tell the operator when the cooking process is complete
They are used in burglar alarm systems to warn if intruders are present
Actuators are transducers and are used to take signals from a computer and convert them into some form of motion, for example operating motors, pumps, switches or valves.

The motors are turned on or off by the actuator
The actuator is connected to the switch that turns the lights on or off.
Actuators are connected to switches which turn the heater on or off.
Heaters are used in automatic washing machines, cookers and central heating systems.
Heaters are used in automatic greenhouses to control the temperature
They are used for security lights
Lights are used in greenhouses to control the lighting conditions
Motors are used in many domestic appliances, such as automatic washing machines and cookers.
In industry, they are used to control robot arms.
In computers they operate disk drives.
Input Devices
As the name suggests, input devices are hardware devices that allow data to be input into a computer. Many such devices exists, ranging from the more common ones, such as a keyboard, through to the more specialist devices, such as barcode readers.
These are the most common input devices and are used to input text, numbers and instructions into the computer .
Keyboards are used to input data into applications software (e.g. text into word processors, numbers into spreadsheets)
They are also used for typing in commands to the computer (like Ctrl + C to copy and Ctrl + V to paste, etc)
Keyboards enable fast entry of new text into a document
They are a well-tried technology and a well-known method of entry
Most people find them easy to use
It is easy to proofread what you've written as it appears simultaneously in the screen
Users with limited arm/wrist use can find keyboards hard to use
Entering data using a keyboard is slow when compared to direct data entry (e.g. optical mark recognition)
Keyboards are fairly large devices that use up valuable desk space
Most of the users use QWERTY keyboards. It is called QWERTY because the keys on the top row, which spell out "QWERTY".
Ergonomic keyboards have also been developed recently. These are designed to reduce health-related problems associated with the standard keyboard (carpal tunnel syndrome)
A numeric keypad is used to enter numbers only (although some have a function key to allow input of alphabetic characters)
Numeric keypads are faster than standard keypads for entry for numeric data.
Since many are small devices, they are easy to carry around
They can be difficult to use, due to very small keys
It is difficult to use them for entering text
Sometimes the order of the numbers on the keypad isn't intuitive

More comfortable
Reduces strain on hands and wrists
Different angles of the keyboard allow your hands to be at a more natural position
May take time getting used to
May have to adjust your typing habits to fit the keyboard
Will not solve all working place injuries
Only frequently keyboard users should invest in one
It is cheap
It is easy to get used to it
It easy to remember where the keys are located
Sold in a wide range of sizes and styles
Can cause illness like the Carpal Tunnel Syndrome
Cheap keyboards don´t last for long
Takes a little amount of time to get used to the keys location
OMR, MICR, Barcode Readers and OCR Devices
OMR Devices
stands for
It is a system which can read marks written in pen or pencil.
OMR devices are used to read questionnaires, multiple choice examination papers and places with answers in the form of shaded areas.
It is a fast way of inputting the results of a survey, etc - the documents are fed in automatically and there is no user input
There is no typing, no typing errors
More accurate than OCR
The forms need to be carefully designed so that the shades are in correct position and there is no errors
If forms are not filled correctly, there can be input and data errors
Barcode Readers
MICR Devices
OCR Readers
stands for
. It is a software that takes scanned text and converts it into a computer readable form. Then, the text can be used in various application packages such as word processors, desktop publishers and presentation software.
One of the most recent uses is in the processing of passports and ID cards
OCR is used when scanning documents so that they can be modified using word processor or desktop publisher package.
it is a much faster data entry system than manually keying data
Since no manual data entry, the number of errors is reduced
The system still has difficulty reading handwriting
It is still not a very accurate technique
Barcode readers are used to read information in the form of a bar code. The readers are usually in the form of a barcode scanner and are often built into POS terminals in supermarkets.
Barcode scanners are used in supermarkets and other shops where the goods are marked with a bar code.
They are used in libraries to keep track of books loan
They are used as a safety function in many companies to ensure that electrical equipment is checked on a regular basis.
Barcodes enable automatic stock control
Barcode scanning is a tried trusty technology
When an item price is changed, only the central database needs to be updated, not the reader
Faster than manually keying
The system is not foolproof - barcodes can be swapped around on items
Expensive as each item must have a barcode and every barcode must be entered in the main database. Good barcode readers are expensive
stands for
. It is a special system that which can read characters printed in a special ink (containing iron particles). These characters are converted into a form that the computer can understand and then stored in a computer file.
It is primarily used to process cheques in baking operations.
MICR offers greater security than OCR since the printed characters cannot be altered
There is no manual input, therefore , errors are reduced
Even if someone writes over the magnetic ink, it can still be read
Only certain characters can be read and the number of different characters is limited
It is a more expensive method than other methods used in direct data entry
The mouse is an example of a pointing device. A ball is used underneath the mouse to detect movement, so by moving the mouse around the user can control the position of the pointer at the screen
Used for grouping, moving and deleting files
Opening, closing and minimising files
Useful for image editing like controlling size and position of the image pasted in the document
The control of the position of the pointer on the screen
It can be faster to select an object rather than a keyboard
Take up little space
Enable rapid navigation through applications and the internet
People with restricted hand/wrist might find them difficult to use
Mice are easily damaged and old mice are rapidly clogged up with dirt
Only work properly on a flat surface.
Trackerballs are similar to a mouse, except the ball is on top of the device and the user controls the pointer on the screen by rotating the ball with the hand. Trackerballs have two buttons just like the left- and right-hand mouse buttons.
They have the same pointing/cursor control capability as a mouse
They are used in applications where the user has a disability
It is more robust than a mouse and used in a control room environment
Do not need the same fine control as a mouse
Easier to use for people with limited hands/wrists
More accuracy in the pointer control and position on the screen
Stationary and take less space than a mouse
Not supplied with the computer, therefore they are more expensive
User may need training since they are not standard equipment
Touchpads are used in many laptop computers as a pointing devices. The pointer is controlled by the user moving their finger on the touchpad and then gently tapping it to simulate the left hand button of a mouse. Under the touchpad, there are two buttons to simulate the buttons of a mouse.
The same as a regular mouse
Can be used in any surface
Since it is integrated into the laptop, it is more comfortable to take it with you
Enable rapid navigation in the internet
More difficult to control compared to mouses
Difficult to do certain operations such as "drag and drop"
People with limited hands/wrists could find them difficult to control
Webcams are similar to digital video cameras; however, they are connected directly to the computer and they don't have a memory. The information picked up by the webcam is directly transmited to the computer.
While chatting online, people may use webcams as a more personal way of having a conversation.
They are used to enable video conferencing to take place.
Webcams can be left on constantly, only being activated as required
Allow people to see each other without them needing to travel long distances
Some computers already contain webcams on top of their monitors.
Webcams have very limited frequencies and the picture is often of a poor quality
They need to be connected to the computer in order to work,
They get easily damaged
The lenses can get dirty or brake, making the image quality poor
Microphones can be connected directly to a computer. Sounds can be inputted and then manipulated. The input sound is converted to an analogue signal and then converted into a digital signal.
Microphones are used to input speech/sounds to be used in various applications, e.g. presentations, sampling (in films and music), special effects (films and video games)
Voice recognition software used for security
Recognition of commands (e.g. systems toswitch lights on and off)
Conversion of speech into text
It is faster to read in a text than to type it in using a keyboard
Using special software, you can manipulate sound in real time rather than prerecorded sound
Improved security with voice activation systems
Voice recognition is very inaccurate
Sound files can use up a lot of computer memory
A sensor is a device which inputs data to a computer from a measurement of a constant physical change in a physical quantity (e.g. temperature, moisture, light, etc)
Automatic washing machines, ovens, automatic greenhouses
Burglar alarm systems, robotics, environmental monitoring
Automatic doors, street lighting control, burglar alarm systems
Monitoring liquid and powder flow in pipes
Automatic greenhouses, factories where moisture is crucial (paint spraying)
Chemical processes, environmental monitoring, automatic greenhouses
Readings taken using sensors are generally more accurate than ones taken by human operators
System is automatic
Readings are continuous
Necessary actions can be taken immediately
Faulty sensors can give spurious, inaccurate results
Smart cards contain chips and are similar to magnetic stripe cards. In these cards, the data is stored on the chip. The data stored in the chip can be updated. The readers contain magnets. When they touch the pins, a signal is transferred to a computer,
Smart cards can be used to track customer/passenger movements.
Used for electronic passports and driving licenses
In public transport
Some smart cards are used instead of money, reducing the need to carry cash
Data is more secure
Less damage compared to magnetic stripe readers since it doesn't need to be in full contact with the reader
If the card is lost, the information stored on the chip could be used in identity theft
They are similar to smart card readers, but are used at EFTPOS (electronic funds transfer point of sale) terminals. The device has a slot into which the card is placed and the chip is read. The PIN is entered using the keypad. It also has a small screen, which gives instructions to the operator.
Chip and PIN readers are used where payments are made using cards.
Chip and PIN readers provide a more secure payment system than requiring a signature or using a magnetic stripe.
It provides a much more robust system, since the chip doesn't need to be in contact with the reader
Be careful nobody reads the PIN number or they could fraud you
Scanners are used to enter information on a hard copy into the computer. The hard copy document or photo is scanned by a light source and produces a computer-readable image. the most common scanner is the flat bed which is made up of a glass panel and lid.
To scan in documents and convert them into a format for use in various software packages
Old valuable documents or books can be scanned, protecting the original text from damage
Non-digital photographs must be scanned if they are to be stored in a computer
Images can be stored for editing at a later date
Scanners are much more faster and accurate than retyping a document
It is possible to restore a damaged photo or document by scanning it and then editing it with a good software to produce an acceptable copy
The quality depends on the scanner's resolution
These are used to read the information on the magnetic stripe found on the back of a credit card for example.The stripe contains useful information, such as the account number, sort code, expiry date and start date.
Credit and debit cards have magnetic stripes that are used by ATMs or EFTPOS (electronic funds transfer point of sale) terminals
Security cards to enter buildings
Trvel systems
It is faster than keying in using a keyboard or keypad
The system is error free, since there is no typing
The data is secure in the magnetic stripe since nobody can read it without a reader
can prevent access to restricted areas
Unaffected by oil or water
If damaged, data is lost
Must be in contact with the reader
Computer systems are now commonplace in every part of our daily life. We will introduces the basic components that make up these computer systems. Comparing books with computers is a good analogy: the actual pages and the ink used on the pages are equivalent to the software
Hardware is a general term for the physical components that make up a computer system, for example keyboard, mouse, monitor, processor, circuit board and so on.
Soft ware is a general term for the programs that make up the computer system. There are two types of software:

System software: programs that allow the hardware to run properly, e.g. operating systems

Applications software:programs that allow the user to do specific tasks, e.g. spreadsheets


The motherboard is central to any computer system.

All components plug into the motherboard either directly (straight into the circuit board) or indirectly (via USB ports).

Once connected to the motherboard, the components can work together to form the computer system.

Components communicate and send signals to each other via the BUS Network.

CPU - (Central Processing Unit)

The Central Processing Unit (CPU) is the brain of the computer.

The CPU 'controls' what the computer does and is responsible for performing calculations and data processing. It also handles the movement of data to and from system memory.

CPU's come in a variety of speeds which are known as 'clock rates'. Clock rates are measured in 'Hertz'. Generally, the faster the clock rate, the faster the performance of the computer.

There are two main brands of CPU currently on the market... AMD and Intel:


RAM (Random Access Memory)

RAM is used to temporarily store information that is currently in use by the computer. This can include anything from word documents to videos.

RAM can be read from and written to and so the information stored in RAM can change all the time (it depends what tasks you are using the computer for).

RAM is a fast memory. Data can be written to and read from RAM very quickly. RAM is generally measured in GB (Gigabytes).

RAM is Volatile Memory. This means that information stored in RAM is deleted as soon as the computer is turned off. Deleted information cannot be retrieved. Click here for an example of this.

The more RAM you have installed in your computer -- the faster it can perform. You can open and use more programs at the same time without slowing the computer down.

ROM (Read Only Memory)

ROM is used to permanently store instructions that tell the computer how to boot (start up). It also loads the operating system (e.g. Windows).

These instructions are known as the BIOS (Basic input/output system) or the boot program.

Information stored in ROM is known as READ ONLY. This means that the contents of ROM cannot be altered or added to by the user.

ROM is fast memory. Data stored in ROM can be accessed and read very quickly.

ROM is Non-Volatile memory. This means that stored information is not lost when the computer loses power.

Other examples of ROM include: ◦DVD/CD ROMS bought in stores containing pre-recorded music and movie files. These are played back at home but cannot be altered.
ROM in printers which is used to store different font types.

The general tasks for a typical operating system include:
supervising the running, loading and storage of applications programs
controlling the operation of the input, output and backing storage devices

CLIs (Command Line Interfaces) require a user to type in instructions in order to choose options from menus, open software etc. There are often a number of commands that need to be typed in for example, to save or load a file. The user therefore has to learn a number of commands every time an operation has to be carried out. however, the advantage of CLI is that the user is in direct communication with the computer and is not restricted to a number of pre-determined options.
GUIs (Graphical User Interfaces) allow the user to interact with a computer using pictures or symbols (icons) rather than having to type in a number of commands. GUIs use various technologies and devices to provide the user interface. One of the most common is windows icons menu and pointing device (WIMP) which was developed for use on personal computer (PCs)
PC/desktop usually refers to a general purpose computer which is made up of separate monitor, keyboard, mouse and processor unit.
The large casing allows good dissipation of any heat build-up
Desktops tend to have better specification
Spare and connections tend to be standardised, which usually result in low cost
Not portable
Components hooked u by wiring, MESS!
Laptop refers to a type of computer where the monitor, keyboard pointing device and processor are all together in one single unit.
Very portable
No trailing wires
Can link to multimedia systems since they are portable
Take full advantage of WiFi
Easy to steal!
Limited battery life
Keyboard and pointing device sometimes awkward to use
Netbook is a term used to describe a computer that can almost fit onto a hand and is a smaller version of a laptop. These were used to be called palmtops.
Same advantages as laptops
Don´t have optical devices
Lack features that can be find in bigger computers
Screen quality and size is low
Personal Digital Assistants (PDAs) are small handheld computers that usually come with a touch screen that is activated using a stylus. Data is entered by using a keyboard that appears on the touch screen.
can be used everywhere because of its size
Difficult to enter text quality
Limited capabilities due to software and operating system used
Mainframe computer is a term used for a large, very powerful, computer system. The name comes from the days when the individual components were housed in large frames.
Capable of large number crunching and deal with very complex mathematical functions
Used in time-sharing systems
can be used to do very large jobs which require large memories
Expensive to operate and maintain
Not portable
Must be housed permanently



What is backing up of data?

Backing up refers to the copying of files and data to a diferent medium (disk, tape, flash drive, etc.) in case of a problem with the main storage device. Backing up files and data on a regular basis is seen as good computing practice and many computing systems can be set back to up files automatically on a regular basis.
The backups are often stored in a different place to the main storage. This is in case of fire or some other situation which could lead to irrevitable loss of key data and files.
Why Back Up Data
Data could be lost due to failure of the original storage device. This could be due to the hardware failure, problems caused by files being over-written accidentally or possible corruption of files.
Hackers could be reponsible for the corruption or even loss of data. This may not be their intention. However, the very act of hacking into files could cause problems such as corruption or data loss.
Backupsare also made in case of the files need to be used elsewhere. The original files are then protected against possible corruption or loss.
Serial Access
With this system, to access data it is necessary to start at the beginning and then access each piece of data in turn until the required information is found. It is primarily used on magnetic tape systems and is a very slow form of access. It is used in applications where speed of access or where the order in which the data is accessed is not important like in utility building. When a magnetic tape needs updating, an additional tape is required so that the the old information can be merged with the new data to produce the updated tape.
This method is used with magnetic disks and with optical media like CDs. The computer uses a key field to calculate where the data has been stored. it is then able to access the data directly from the calculated position. It is faster than serial access. It is used in applications in which speed is vital like online ticket booking. When updating media which uses direct access, the new data is written to the next available location and its position is calculated using the built-in algorithm.
Direct Access
Backing Storage Media
When a user types data into a computer, the information is stored temporarily on the RAM-however, this information would be lost as soon as the computer was turned off. Backing storage devices ensure that data is stored permanently and be used at a later date. Backing storage devices are either internal or external (e.g plug-in devices) to computer, and are one of three types:
Solid State
Fixed Hard Disk
Portable Hard Disk Drives
Floppy Disk Drives
Magnetic Tapes
Hard Disks
Optical Storage Media
CDs and DVDs
Blu-ray Disks
Fixed hard disk drives are available on all computers and are the main method used for data storage. On a PC this usually a fixed had disk with read/write heads allowing data to be written to or read from the disk surface. The disk surface is coated in a magnetic film which allows data to be stored by altering the magnetic properties to represent 1s and 0s. The hard drive disks usually store the
disk operating systems (DOS).
Fixed hard drives are used to store the operating system and working data.
They are used for servers in computer networks.
They are used for storing applications software that needs fast retrieval and storage of data.
They have very fast data transfer rate and fast access times to data.
They have very large memory capacities.
They can be fairly easily damaged
They lack portability unless a portable hard disk drive is used.
These deices work in much the same way as fixed hard disk drives but are usually connected to the computer via a
universal serial bus (USB)
port and can be disconnected and used on different computers. The disks are generally capable of storing more data than the equivalent optical disk (CD, DVD and so on).
Floppy disks are still used on some computer systems. They consist of a thin disk of plastic which is housed in a plastic case with a window where the disk can be accessed. As the disk rotates, a read/write head is used to add or read data stored on the surface.
A magnetic tape is a very thin strip of plastic which is coated in a magnetic layer. They are read and written to by a read/write head. The data is stored in magnetic areas which represents 1s and 0s. Data is written to and read from the tape in sequence. This is known as serial access.
Portable hard disks can be used as back-up systems to prevent loss of data.
They can be used to transfer data, files and software between computers.
They are still used where small files need to be transferred/stored.
Some older computer systems still make use of this method of storage.
Magnetic tapes are used in applications where batch processing is used, for example in clearing banks cheques, utility billing and producing pay slips. In these applications, there is no need for any specific.
They are used as a back-up media since all the data needs to be stored.
The data access time and data transfer rate is very fast.
They have large memory capacities.
Can transfer the same data to different computers.
Using a CD to store a small file is usually wasteful if you have a floppy disk drive.
Simple technology and cheap.
They generally less expensive than the equivalent-capacity hard disk.
It is a very robust technology.
The data transfer rate is fast.
As with fixed drives, a portable hard disk can be easily damaged if the user accidentally drops it or does not shut it down correctly after use.
Floppy disks have a very low memory capacity when compared to CDs/DVDs .
Very few modern computers don't have floppy disk drives.
The data transfer rate is slow compared to more modern data storage devices.
Floppy disks are not very robust.
Access time is very slow.
When updating, another tape is needed.
CD-R and DVD-R
CD-ROMs and DVD-ROM's are read only memory (ROM), which means they cannot be written over and can only read. The data is stored as series of pits (1) and lands (0) in the metallic optical layer. The pits are formed by a laser etching the surface at the manufacturing stage. Only a single spirals out from the centre of the disk. The pits and lands are read by a low-powered laser beam.
The letter "R" here means the disk is recordable once only and becomes a CD-ROM or DVD-ROM.These use a thin layer of an organic dye as the recording media; DVDs also use an additional silver alloy or gold reflector. A laser beam produces heated spots and unheated spots. On a reading the disk, a laser beam is capable of distinguishing between the two types of spots and effectively reads the data stream from the centre outwards in a spiral action. This data is interpreted as "1" and "0".
The "RW" means that these disks are re-writable media and can be written over several times. Unlike CD-Rs/DVD-Rs they don't become ROMs. The recording layer uses a special phase-changing metal alloy. The alloy can switch between crystalline and amorphous phases, ths changing its reflectivity t light, depending on laser beam power. Spots are produced which can be read by a laser and then interpreted as "1" and "0". This system allows data to be written, erased and re-written many times.
CD-ROM's are used by manufacturers to store music files and software, computer games and reference software.
DVD-ROM's have much larger storage capacity than CD-ROMs and are used to store films. They are now increasingly used to store computer data and ever-more sophisticated computer and arcade games.
They are used for home recordings of music and films.
They are used to store data to be kept for later use or to be transferrs to another computer.
They are used in applications where it is necessary to prevent the deletion or over-writing of important data.
CD-RWs and DVD-RWs are used to record radio and television programmes, but can be recorded over time and time again.
They are used in closed circuit television (CCTV) systems.
They hold far more than floppy disks, so one CD/DVD could replace several floppy disks in some applications.
They are less expensive than hard disk drive systems.
The data transfer rate and data access time are slower than for hard disks.
CD-Rs and DVD-Rs are cheaper than RW disks.
Once burned (and finalized), they are like ROM disks.
They can only be recorded once, so if an error occurs then the disk has to be thrown away.
Not all C/DVD players can read CD-R/DVD-R.
CD-RWs and DVD-RWs can be re-used many times.
They can use different file formats each time they are used.
The RW format is not as wasteful as the "R" format since files or data can be added at a later stage.
CD-RWs and DVD-RWs can be relatively expensive media
It is possible to accidentally overwrite data.
DVD-RAM is a recent addition to the optical media group. Unlike other CD and DVD formats, DVD-RAMs have several discrete concentric tracks rather than a single spiral track. This gives them the advantage that writing and reading can occur at the same time. This makes it possible to watch an already recorded television programme at the same time as a different programme is being recorded.
DVD-RAM's are used in recording devices such as satellite receivers to allow simultaneous recording and playback.
They are used in camcorders to store films.
DVD-RAM's have a long life-minimum life is estimated to be 30 years.
Access is very fast if the files are fairly small.
They have a large capacity (5-10 Gbytes).
Can read data at the same time is being written.
DVD-RAM's are not as compatible as "R" or "RW" format, as many systems will not recognise their format.
They are relatively expensive, costing about 4 times as much as a DVD-RW disk.
Blu-ray disks have the largest capacity of all te optical media available and go up to 100 Gbyte. The laser beam used is the blue/violet and of the spectrum, rather than red which is the colour of the lasers used in other optical media. Consequently, the light used has a shorter wavelength, allowing more data to be stored/read on the disk.
Blu-ray disks are used in home video consoles.
They are used for storing and playing back films: 1 high-definition film of two hours duration uses 25 Gbytes of memory.
PCs can use this technology for data storage or backing up hard drives.
Camcorders can use this media (in cartridge form) to store film footage.
They have a very large storage capacity, and so are ideal for storing high definition films.
The data transfer rate is very fast.
The data access speed is also greater than with other optical media.
The disks are relatively expensive.
At the time of writing, blu-ray systems still have encryption problems (which are used to stop piracy) when used to store video.


Most computer systems are now connected together in some way to form what is known as a network. This ranges form the basic school/home network of only a few computers to large networks such as the internet which effectively allows any computer similarly connected.

Most networks are controlled by the use of servers. There are different types of servers, for example:
File servers, which allow users to save and load data/files
Applications servers, which deal with the distribution of applications software to each computer.
Printer servers, which ensure printing from devices on the network is done in a queue, for example.
Proxy servers, which are used as a buffer between WAN's (wide Area Network) and LAN's (Local Area Network)
Common Types of Networks
A local area network (LAN) is usually within one building or certainly not over a large geographical area. A typical LAN will consist of a number of computers and devices like printers which will be connected to hubs or switches. One of the hubs or switches will usually be connected to a router and modem to allow LAN to connect to the internet; in doing so it then becomes part of a wide area network (WAN).
The sharing of resources (such as expensive peripherals and applications software)
Communication between users
A network administration to control and monitor all aspects of the network (changing passwords, monitoring internet use and so on).
Easier spread of viruses throughout the whole network.
The development of printer queues, which can be frustrating.
Slower access to external networks, like the internet.
Increased security risks when compared to stand-alone computers.
The fact that if the main server breaks down, most cases the network will no longer function.
There are four common types of LAN network topologies: ring, bus, star and tree networks.
Types of Networks
Ring Networks
Ring networks are becoming less popular. Every computer in the network is connected in a ring, including the server. Data is transmitted around the ring and each computer only removes the data which is relevant to it. This allows each computer to send and receive data since they all have a unique identification/address.
Ring networks work well under heavy loading.
It is possible to create very large networks using this topology.
If there is a fault in the wiring between two computers then the whole network will fail.
Adding a new device or computer to the network can be difficult since it has to be placed between two existing devices.
Bus Networks
Star Networks
Tree Networks
It is easy to add a new computer or device to the network.
If one device or computer fails, it does not affect the rest of the network.
This type of network doesn't need a hub or a switch and also requires less cabling than, for example, a star network, so it has a lower cost.
Te same as star and bus networks as tree networks are a combination of both.
If one computer or device fails, then the rest of the network is unaffected.
Problems on the network are easy to identify and work can be carried out on a faulty device without affecting the rest of the network.
It is easy to expand the network.
It is difficult to isolate any fault on the network.
If the central line has a fault then the whole network fails.
This is becoming an increasingly outdated topology for network design.
Its performance worsens noticeably as more and more devices/computers are added.
In a bus network each computer or device is connected to a common central line. Data travels along this central line until it reaches the computer or device that requires it. The ends of the line have terminators to prevent, for example, signal bounce, which would cause data interference.
Te same as star and bus networks as tree networks are a combination of both.
If the central hub breaks down, the whole network crashes
With a star network, each computer or device is connected via central hub or switch. Data is sent to the hub which then sends out data along every cable to every computer or device and no checking is done to see where the data should be sent.
Tree networks have a central line connecting together a series of star networks. The server is also connected to this central line. Because of its flexibility, and the fact that it has the advantages of both bus and star networks, this topology is becoming increasingly popular.
WLAN, WiFi, Bluetooth and WAN
Wireless LANs or (WLAN) are similar to LANs but there are no wires or cables. In other words, they provide wireless network communications over fairly short distances using radio or infrared signals instead of cables.. Devices, known as access points (APs), are connected into the wired network at fixed locations. Because of the limited range, most commercial WLANs need several APs to permit uninterrupted wireless communications. APs have very short range and its infrared signal can be easily blocked.
Bluetooth is an example of wireless personal area networking (WPAN) technology. Spread spectrum transmission (radio waves) is used to provide wireless links between mobile phones, computers and other handheld devices and allow connection to the internet.
With this system, it is possible to create a small home network, for example, to allow communication between any PDA, mobile phone, computer, media player and printer. The range is however, quite small. Examples of its use include the transfer of photographs from a digital camera to a mobile phhone or the transfer of phone details to a computer. It behaves like a mini-LAN.
A wide are network or (WAN) is basically formed by a number of LANs being connected together through either a router or a modem. Some companies will set up private WANs (usually by way of fibre optic cabling or telephone wires restricted to company use only). This is expensive but comes with the advantage of much enhanced security. It is more common to use an internet service provider (ISP) for connections to the internet and communicate via this network system.

The following hardware is needed for a WAN: routers, modems and proxy servers.
WiFi refers to any system where it is possible to connect to a network or o a single computer through wireless communications, for example:
On a WLAN described above.
PDAs and other handheld devices.
Laptop computers which are WiFi enabled.
Preripheral devices like printers and scanners.
WiFi systems rely on some form of AP,which uses radio frequency technology to enable the device to receive and send signals.
WiFi hotspots are places where you can access WiFi. They exist in public places such as airports, hotels and internet cafés. It is possible to log on free WiFi hotspots unless they are protected by passwords. The practice of driving around in a car looking for these unsecured WiFi hotspots is known as war driving and poses security risk to any unsecured WiFi system.
All computers can access the same services and resources like printers, internet and scanners.
There is no cabling to individual computers and devices so safety is improved.
The system is more flexible, since users can move their laptops from their desks.
Adding more computers or devices is very easy.
Security is a big issue since anyone with a WLAN-enabled laptop can access a network if it can pick up a signal. It is necessary to adopt complex data encryption techniques.
There may be problems of interference which can affect the signal.
The data transfer rate is slower than in a wired LAN.
Network Devices
Modem means modulator demodulator and is a device which converts a computer's digital signal into an analogue signal for transmission over an existing telephone line. It also does the reverse process, in that it converts analogue signals from a telephone line into digital signals (demodulates) to enable the computer to process the data. Modems are used to allow computers to connect to networks over long distances using existing telephone networks.

Dial-up modems operate at transmission speeds of about 60 kilobits per second, which is quite slow by today's standards. However, modern broadband or asymmetric digital subscriber line (ADSL) modems operate at 11000 kilobits per second. It is called asymmetric because it is faster downloading than uploading data.

ADSL modems can allow telephone conversations and internet traffic to occur at the same time because of the wide bandwidth signal used: the higher frequencies are used to carry at same because of the wide bandwidth signal used: the higher frequencies are used to carry the internet signals, so they do not interfere with normal telephone traffic. Cable modems also exist which allow cable television providers to offer internet access as well as receiving television signals.

Network Hubs
Network are hardware devices that ca have a number of devices/computers connected to them. Its main task is to take any data received via one of the ports and send out this data from all of the ports. Each computer/device will receive data, whether it is relevant or not.
HTTP Proxy Servers
Bridges are devices that connect one LAN to another LAN that uses the same protocol (the rules that determine the format and transmission of data). They decide whether a message from a user is going to another user on the same LAN or to a user on a different LAN. The bridge examines each message and passes on those known to be on the LAN and forwards messages meant for a user on a different LAN. In networks that use bridges, workstation address are not specific to their location and therefore messages are actually sent out to every workstation accepts this message. Networks using bridges are interconnected LANs since sending out every message to every message to every workstation would flood a large network with unnecessary traffic.
Switches are similar to hubs but are more efficient in the way they distribute data. A hub learns which devices are connected to which ports. Each device has a media access control (MAC) address which identifies it uniquely. Data packets sent to the switch will have a mac address giving the source and receiving device. If a device X is always sending the switch data via port then it learns that X must be through port 4 and not through any of the others. This means that the network traffic only goes to where it is needed and so a switch is more efficient than a hub, especially when the network is very busy.
Since large companies often have more than one network there are occasions when the computers in one network want to communicate with the computers in one of the other networks. Routers are often used to connect the LANs together and also connect them to the internet. Routers inspect the data packages sent to it from any computer on any of the networks connected to it. Since every computer on the same network has the same first part of an internet protocal (IP) address, the router is able to send the data package to the appropriate switch and it will then be delivered using the mac destination address in the data packet . If this mac address doesn't match any device on the network it passes on to another switch on the same network until the device is found.
This is a special type of server that acts as a buffer between a WAN and a LAN. The server passes on the service requests to the internet and then passes them back the requested pages. it therefore retrieves web pages and passes them on to the computer that made the request. Any page retrieved from the internet is stored on the server, which means that when a different computer requests the same page it is available immediately thus considerably speeding up the browsing process.
The Internet
The internet is a worldwide collection of networks which allows a subscriber to send and receive emails, chat or browse the world wide web. The world wide web (WWW) is the part of the internet which the user can access by way of a web browser like Google Chrome. A web browser is software that allows the user to display and interact with pages and files from the web.
Accessing The Internet
The web is made up of millions of websites and millions of web pages. Web pages are documents on a computer screen which may consist of text, pictures, sounds, animations or videos. A website consists of many of these pages linked together.
The website shows hyperlinks to allow users to navigate between web pages. These hyperlinks are often shown as
blue underlined text
or sometimes a small hand appears under a picture or under some text indicating the link to another page or website. The user clicks on these hyperlinks using a mouse to move to another page. Web browsers use uniform resource locations (URLs) to retrieve files. URLs are a standard way of locating a resource on the internet ; they are usually a set of four numbers. However, as this can be difficult to remember, an alphanumeric form is usually used which has the format: protocol://site address/path/filename
protocol is http
Site address consists of computer name, domain name, domain type and country code:
computer name is usually www
domain name id the name of the website
domain tyoe is commonly .com, .org, .net...
country code like .uk, .es, .cy
Path is the web page
Filename is the item on the webpage

So, a full URL would be: http://www.urlexamples.co.es/pages/example1
An ISP is a company that provides users with access to the internet, usually for a fee. When a user registers with an ISP, an account is set up and they are given login details, which include a username and a password. The user connects to the internet via the user account which also allows the provider to monitor usage. Most ISPs also provide an email account. Emails are an electronic way of sending documents from one computer to another. They allow attachments, which can be word-processed documents, spreadsheets, data files, music files, movie files, etc. An email address contains to parts:

example1@yahoo.co.uk OR example2@yahoo.com

The first part is the user name (example 1 and example2) and the second part is @ followed by the host name (@yahoo.co.uk and @yahoo.com) Emails are three common ways of accessing the internet offered by service providers:
Dial-up internet access
Cable internet access
Digital subscriber line (DSL) (broadband) internet access.
Many companies use an intranet as well as the internet. The definition of an intranet is "a computer network based on internet technology that is designed to meet the internal needs for sharing information within a single organization/company". There are number of reasons for doing this.
It is safer since there is less chance of external hacking or viruses.
It is possible to prevent employees from accessing unwanted websites.
Companies can ensure that the information available is specific to their needs.
It is easier to send out sensitive messages that will remain only within the company.
It is possible to lock down certain internet sites using an intranet.
An intranet requires password entry and can only be accessed from agreed points so it is much safer.
Network Security
To protect your network you can use the following things:
User ID
Authentication Techniques
User IDs
Authentication Techniques
When logging on to any network system, a user will be asked to type in a user ID. This assigns the user privileges once the logon procedure is successful. For example, on a network, top level privilege would be for an administrator, who is able to set passwords, delete files from the server, etc., whilst a user privilege may only allow access to their own work area.
After keying in the user ID, the user will then be requested to type in their password. This should be a combination of letters and numbers which would be difficult for somebody else to guess. When the password is typed in it often shows on the screen as ****** so nobody overlooking can see what the user has typed in. If the user's password doesn't match up with the rest of the user ID then the access will be denied. Many systems ask for the password to be typed in twice as a verification check. To help protect the system, users are only allowed to type in their password a finite number of tries to logon until the system administrator has re-set their password. When using some internet websites, if a user forgets their password they can request the password to be sent to their email address. The password is never shown on the computer screen for reasons of security.
Encryption is the converting of data into a code by scrambling it or encoding it. This is all done by employing encryption software (or any encryption key). Since the data is all jumbled up it appears meaningless to a hacker or anyone who illegally accesses the data. It should be stressed that this technique does not prevent illegal access, it only makes the data useless to somebody if they don't have the necessary decryption software or decryption key. It is used to protect sensitive data such as people´s details. The system works like this:
A user writes a message and the computer sending this message uses an encryption key to encode the data.
At the other end, the receiving computer has a decryption key which it uses to decode the message . Note that the date when the message was sent is important since this formed part of the encryption algorithm.

Encryption keys are very complex in order to prevent computers being used to crack the code. Very sophisticated algorithms are used which make the codes almost unbreakable.
As shown above, there are many ways in which a computer user can prove who they ae. This is called authentication. Most systems adopt the following authentication logic:
Something you know-example PIN/password
Something belonging to you-example a bank card
Something unique to you-example your fingerprints.
This methods are used in places like banks.
Communication Methods
Many methods of communication using networks exist. These include fax, email, video conferencing and VOIP
Video Conferencing
The term fax is short for the word "facsimile". With this system, documents are scanned electronically and converted into a bit map image. This is then transmitted as a series of electrical signals through the telephone network. The receiving fax machine converts this electronic image and prints it on paper. It is also possible to genera fax signals from a computer to allow files and documents to be sent to a fax machine- this saves printing out the document first and then passing it through a fax machine . Fax/modem software in the computer converts the image into a form recognized by a fax machine. However, this is not efficient as the email system where the electronic copy is sent and is then stored electronically thus permitting the document to be edited.
This is an electronic method for sending text and attachments from one computer to another over a network.

The advantages of using an email include:
The speed of sending and receiving replies using the email system.
The low cost, since stamps, paper and envelopes are not needed.
The inability to send bulky objects via email.

The disadvantages include:
The possibility of virus threats and hacking .
The need for the email address to be completely correct.
The inability to send bulky objects via emails.
This is a method of communication between people at two separate locations. This is done in real time and makes use of LAN, if internal, or through WAN, example the internet, if national or international. The system works in real time and uses additional hardware such as webcams, large monitors/television screens, microphones and speakers.
The system also uses special software such as:
CODEC, which convert sand compresses analogue data into digital data to send down digital lines.
Echo cancellation software, which allows talking in real time and synchronizes communications.

Delegates at one end speak into a microphone and look at a webcam. The other delegates can see them and hear them using large monitors and speakers.
Voice over internet protocol (VOIP) is a method used to talk to people using the internet. VOIP converts sound into discrete digital packets which can be sent to their destination via the internet. One of the big advantages is that it is either free or a local rate to anywhere in the world. To work in real this system requires a broadband ISP. The main problems are usually sound quality. Security is also a main concern with VOIP, as it is with other internet technologies. The most prominent security issues over VOIP are:
Identify and service theft
Viruses and malware
Phishing attacks


Types Of Data
Data exist in many forms, and so there are various types of data that computers use. All the data that is stored on computers is digital, but lots of types of data in real world involve physical measurements of continuously varying data. These need to be converted into digital data for storage and manipulation on a computer. data frequently needs to be stored in a logical sequence to allow access and/or searching to be done at some later stage. One of the most common methods of data storage is the use of databases. There are several data types found in most computer systems:
Alphanumeric and Text Data
Numeric Data
Date Data
Boolean data (or logic data type) can have only two: true and false. This works if there are only two possible responses to a question or situation, i.e. (Yes or No), (True or False) or (1 or 0). This is made most use of when carrying out a search in a database or on the internet. In these cases, logical operators are used which are based on true (i.e. binary 1) or false (i.e. binary 0) logic.
Looking at a standard keyboard, you see the letters A to Z, the digits 0 to 9and other characters such as: @ & $ ) ] etc. The letters A to are referred to as text and the letters A to Z plus the digits 0 to 9 are referred to as alphanumeric (some definitions also include the remaining keyboard characters such as @ & $ ) ] as parts of the alphanumeric character set). For example, the password "MARQUES" contains letters only and is therefore alphanumeric. Person's name would always be text but their address, which could contain letters and numbers, would be alphanumeric.
Numeric data can be in two forms: integer (whole numbers) or real (containing decimals). For example, 34.16 is real. Examples of od integers include the number of floors in a hotel, the number of students in a class or the number of wheels in a car. Examples of realnumbers include temperatures, price of an item in a shop or person's height in meters . Numeric data also includes zero 80) and negative numbers such as -4516 (integers) or -30.26 m(real).
Date data can be written in mmany forms, for example:
dd/mm/yyyy (dd=day mm=month yyyy=year)
dd/mm/yy (14/01/99)
dd.mm.yy (15.09.19)
yyyy-mm-dd (2009-04-26)

All of the above examples use a number form of the month, but it can also be written as the full word or the three-letter abbreviation:
dd mmmm yyyy ( 18 December 2012)
dd-mmm-yyyy (12-Dec-2013)

All the above are accepted as date in most application packages (such as spreadsheets asnd databases) where the format is particularly important due to data manipulation (e.g. sorting) or searching.
Data is often stored in files, which consist of records, which in turn consist of fields. For example. a company may have set up a file to include information about their employees in the following format:
reference number/name/date started/ department
A file is divided by records and each record by fields. The first field in a record is called key field or primary field. This type of file is called flat file structure
Data Structures
A database is a collection of information which is structures in some way to permit manipulation and searching of data.
Why are Databases Used
Relational Databases
They promote data consistency. When data is updated on a database it is up to date for any application which uses the database.
Data duplication is reduced to a minimum since only one copy of each data item needs to be kept.
It is relatively easy to expand the database if some new application is being considered.
Security of data is easier to monitor and maintain. Data access can be controlled by database front ends; the actual database will be "invisible" to all users except the database administrator.

Early databases were examples of flat file structures. The way the data is organized makes it difficult to search for a specific piece of information or to create reports which only contain certain information (fields) from each of the records.
Relational databases were first introduced in 1970 following the work of F. F. Codd, a researcher at IBM. Relational databases consist of a number of separate tables which are related (a table is made up of rows and columns in much the same way as a separate tables which are related (a table is made up of rows and columns in much the same way as a spreadsheet is structured). Each table contains a primary field that is also a field in a least one other table. It is possible to combine data from different tables to produce a report which only contains the required information. Relational databases do not need to repeat data, which is one of the problems of flat file structure. Information is stored in separate tables only connected by the primary field. Other advantages of relational databases include:
Faster data retrieval (because of links between tables)
Easy expansion of the database by adding extra data or new tables.
The need to change data in only one table-all other references to this data will then also be up to date, resulting in what is known as data integrity.

Tables can also contain foreign keys that relate tables in the database to one another. A foreign key in one table is a primary key in another. We will now look at an example that shows the structure of tables in a relational database. In this example, there three connected tables. It is important to note that in commercial databases there will be several tables connected together. The examples shown here contain only two or three and are being used to show the principle of relational databases.
Analogue and Digital Data
Computers work with digital data. However in the real world, physical measurements are not digital but are continuously variable, producing an infinite number of values within a given range. For example, length, height, weight, temperature, pressure etc. can take away the value, depending on the accuracy to which they are measured. These values are measured by an analogue device which represents physical measurement on a continuous analogue scale. The data is known as analogue data. Most control and monitoring applications use devices called sensors to measure these physical, analogue quantities. However, computers can only understand and manipulate digital data. Analogue data would not make any sense to the computer and may even cause some damage. To enable data in analogue form to be processed by a computer, it needs to be changed into digital form. This is done using an analogue to digital converter (ADC).
Alternatively if the computer is being used to control a device, such as a motor or a valve, the device may need to be controlled by continuously variable voltages. There would be no use sending out a digital signal, requiring another device, known as a digital analogue converter (DAC).

Example of a Control System
This example shows why there is need to convert analogue to digital and also digital to analogue as part of control system involving a computer. A sensor is used to measure temperature in the furnace and it sends readings in analogue form (small electric currents/voltages). This data is converted into digital by an ADC and is fed to a computer, which compares the input temperature with the required temperature stored on a file. If any action is needed (furnace temperature is too low or too high) then a digital signal is sent out from the computer. This signal is converted into an electric current/voltage (i.e. analogue) so that the valve can be regulated (i.e. opened or closed to control the gas supply and hence the furnace temperature).





Full transcript