Now a days different types of keyboards are available in the market to meet the needs of the users for example ergonomic keyboard is more efficient for those users who suffer from the strain injury or for those who uses a keyboard for long period of time the other example could be a touch sensitive keyboard which is known as a concept keyboard is often used by young children and disabled people.
Mouse
Mouse is another commonly used and important input device, which controls an on screen cursor (arrow). We use a mouse to run a program by double clicking (pressing the mouse button twice) on its icon, selecting text by holding the mouse button and dragging the mouse along the text, moving an image of text from on line to another these are all the functions performed by a computer mouse. In the past a keyboard was used to do all the function a mouse does for us now. Doing things with a mouse will save us much time rather then doing it with a keyboard.
A mouse is designed to fit our hand has one, two or three buttons at the top. As we move the mouse on a mat the on screen cursor moves as well according to our hands movement. A standard mouse has a rubber ball inside to control the movement of the cursor.
More advance mouses are available today such as mouse with optical sensor, which can be used on any kind of surface and cordless mouses that relies on radio technology.
Scanner
A scanner is used to transfer text, symbols and picture from the paper into the computer. A scanner uses light sensitive elements to scan what is on the paper and send it to the computer. As the number of the light sensors elements inside the scanner increases the more detailed the quality of the scanning will be. A scanner, which uses 1200 light sensor elements, will scan 1200 dpi (dot per inch). Dpi decides the quality of the scanning.
The popular type of scanners we usually use at home is the flat bed scanners, which operates as a photocopier. The type of scanner used for a business is the sheet-feed scanners, which are very fast.
Output devices
Output devices let us see the data we have entered into the system. For example we entered some data through a keyboard after the computer processed the data we can see the result on the screen. Widely used output devices are:
Monitors
Monitor is the most important output device. Monitor displays image, character like as we see things on a TV screen. A monitor is sometimes called a CRT (Cathode Ray Tube). A monitor produces a soft copy with means that when we turn the computer off we will lose everything, which was on screen.
Monitors come in different sized 15, 17, 19 and 21 inches. The distance between the two corners of its screen determines the size of a monitor.
The quality of the picture on a monitor can be determined by its resolution. Resolution is measured in pixels (picture elements). One pixel is the smallest unit that can be displayed on the screen. The more the number of pixels the higher the resolution and the better the quality of the picture.
The picture on screen should be refreshed otherwise it will fade ad disappears. The picture must be regenerated which is known as refresh rate. The re refresh rate of a monitor is measured in MHz (millions of cycles per seconds). Most monitors now have refresh rate of 70, 75 or 85 MHz. The higher the refresh rate the less the image flickers.
Printers
Printer is an output device, which provides a hard copy of what is on the screen. Tow types of printers are most in use today inkjet and laser printer.
Laser printers use dry ink or toner. This printer uses electrical charge and perfumes the printing. Inkjet printers use liquid ink. The quality of the printing is resolution, which is measured in dpi (dot per inch) the more the dpi the better the quality of printing.
The speed of the printer is decided by the number o pages per minute (ppm) laser printers speed varies from 8 to 17 ppm of more and inkjet printers speed is between 6 and 10 ppm for black and white but slower for colour printing.
Processor
The processor is the brain of the computer. It is a chip made of silicon composed of tiny electrical switches.
The processor carries the commands you give to the computer, execute programs and do the calculation at a very high speed.
The speed of the processor is measured in MHz (millions of cycles per second). MHz is pronounced megahertz. The more the number of MHz the highest the speed of the computer the faster the computer will execute the commands. Intel is one of the world biggest producers of computer processor. The fastest computer we can buy is Intel Pentium 4 2.2 GHz (1GHz=1000 MHz).
Intel Celeron AMD is the other leading manufacturer of computer processor.
Storage devices
A storage device is used to store programs and other files we create permanently and for future use. A storage device is just like a folder where you put your work and can access it any time u want. The most commonly used storage devices are:
- Hard drive
- Floppy drive
- CD-ROM
Hard drive
Hard drive is the most commonly used storage device where we can store programs, documents we create in different applications, images, digital sound and even movie clips. A hard drive is made of one or more round rigid disk called platter. Each platter has head, which reads the information from the platter, and also the same head stores data on the platter this head is called read/write head if a hard drive has 5 platter so there are 5 read/write head.
Hard drives store a massive amount of data and the access to that data is faster then a floppy disk. The capacity of a hard drive is measured in GB (gigabytes).
Hard drives are stored in sealed units in order to protect them from contaminants and damage.
It is worth mentioning that a hard drive is an input and output device.
Floppy drive
A floppy drive is a removable storage device. A floppy disk is cheap easy to carry and easy to use device. A floppy disk enables us to have our important files always with ourselves but the limitation is that the maximum amount of data we can store on a floppy disk is 1.44 MB. Modern zip drives has solved this problem for us now we can store up to 250 MB of data on the modern floppy disks. Floppy disks are made of a substance called Mylar, which have a magnetic surface and kept in a plastic shell.
Before storing data on a floppy disk we have to format the disk first to establish tracks and sectors into which data can be stored.
To protect the data stored on a floppy disk we should always keep floppy disks away from dust, extreme temperature, moisture and should not be stored near magnetic fields (telephone, television).
CD-ROM
CD-ROM (Compact Disk Read Only Memory) is a storage device. A CD-ROM uses laser beam to read the data from the optical disc. A CD holds up to 650 MB of data, which is equivalent to about 450 floppy disks.
CD Re-writer is available which enable us to store data on a CD. Now we can make copies of music on a CD. CD Re-writers are widely used for backing up hard drive.
Memory
Memory is a chip inside the main processing unit, which is used to store data and programs permanently or temporarily for fast access. There are two types of memory:
ROM
ROM (Read Only Memory) is a permanent memory. The program stored in ROM is always available whether the computer is on or off. Boot program is stored in the ROM when computer is manufactured we can read the data cannot be changed.
RAM
RAM (Random Access Memory) is another type of memory it is also called a volatile of temporary memory because it stores programs and data when computer is running but when we turn off the computer all programs and files are lost. We must make sure we save all our files we have created before turning the computer off.
The capacity of RAM is measured in MB (megabyte). Today computers are available with 128, 256 and 512 MB of RAM.
Appendix
Bibliography:
I have taken all the information from:
Heinemann
GNVQ
Intermediate
Information and communication technology
Molly Wischhusen. Janet Snell
Andrew Scales
