A computer may have many internal and external parts involving in different functions, but it has four main parts :
- Input Devices
- Processing Unit
- Output Devices and
- Storage Devices
As the name suggests Input device is used to enter raw data into the computer, Processing unit will work on that data according to commands or our instructions. Output device will display the processed data or result to us and storage device is used to store/hold these data into the computer so that we can retrieve whenever it will be required.
Now let's discuss these in details.
1. Input Device : There are so many input devices may attached to our computer system to enter the raw data into the computer. Keyboard and Mouse are very common in all. Take a look here at some of the input devices.
Keyboard : Christopher Sholes invented the first practical typewriter and introduced the layout of keyboard. It is used to type letter, numbers, special characters, mathematical operators, symbols or for giving command as keyboard shortcuts (ctrl+c, ctrl+v, Alt+o, f2 etc)
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| Keyboard |
A QWERTY type keyboard has 104 buttons in it. We can categorize then in
Alphabetical keys - A to Z buttons
Numeric keys - 0 to 9 buttons
Function keys - F1 to F12 keys
Special keys - ctrl, shift, delete, alt, esc etc.
Arrow keys - ←, ↑, →, ↓
Toggle keys - caps lock, scroll lock etc
Mouse : Mouse is used to point, select or open a file/folder, and to draw anything or to move objects from one place to other by dragging. It was developed by Douglas Engelbart and Bill English in 1960 and was patented on November 17, 1970
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| Mouse |
A mouse has two button (left and right buttons) and a scroll wheel present between two buttons. Left button is used to point, select, open or move any file/folder or draw anything while right button is used to give commands related to present data like cut, copy, delete, insert etc. When we press right button, it opens up context menu from which we can select any command. Scroll wheel is used to scroll the screen up and down.
Joystick : Joystick are often used to control video games. It has a stick pivot on a base and reports its angles and directions to the device it is controlling. It has one or more than one push-button whose state can also be read by the computer. Joysticks are also used to control the cranes, trucks, underwater unmanned vehicles etc.
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| Joystick |
The other names of Joysticks are Flight Stick and control column. It is originated as controls for aircraft ailerons and elevators and it was Louis Bleriot's Bleriot VIII aircraft in which Joystick was first seen in 1908.
Light Pen : A light pen is a light sensitive computer input device used to draw objects, select text directly on the screen as we write with pen in a notebook. It is known as 'stylus'.
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| Light Pen |
It works well with CRT screen but not very compatible with LCD or LED. So now a days it is discarded or less used.
Touchpad : It is used to move the mouse pointer with our finger. As we move our finger on the flat surface of the touchpad, the mouse pointer also moves in same direction.
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| Touchpad |
We often see it in laptop. We also call it 'trackpad'. It works with a capacitive sensing technology which can detect the finger tip either covered with gloves but can't detect a pen or a pencil or other things.
Microphone : It is used to record voice, music or sound into the computer. Microphone uses its diaphragms to pick up the sound wave and converts it into electrical signal.  |
| Microphone |
Scanner : It is used to input picture into the computer. Scanner is an electronic device which can capture images from physical devices and convert them into digital format and store into the computer.
Modern scanners come in handheld, feed-in and flatbed types and are for scanning black-and-white only or color.- Flatbed scanners are the most common type of scanner. They are called "flatbed" because the document is placed on a flat surface for scanning. Flatbed scanners can scan documents of various sizes and are generally more versatile than sheetfed scanners.
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| Flatbed Scanner |
- Sheetfed scanners are designed to scan documents fed into the scanner one at a time. Scanners with automatic document feeders are smaller and more portable than flatbed scanners and are often used in home offices or small businesses.
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| Sheetfed Scanner |
- Handheld scanners are portable scanners that are smaller than flatbed scanners. They are designed for scanning documents on the go, such as newspaper articles or printed photos.
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| Handheld Scanner |
- 3D scanners are a bit different than traditional scanners in that they collect distance point measurements from a real-world object and translate them into a virtual 3D object.
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| 3D scanner |
2. Processing Device : The processing unit of a computer is Central Processing Unit (CPU). The CPU is present inside the CPU cabinet and does all the calculations of the computer. We all know what our brain do for us, it remember things, take decisions, can calculate and do many other things. The CPU is the 'brain' of the computer. The computer does all its work through CPU (Microprocessor). |
Inside look of a CPU box
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Lets travel inside the CPU cabinet. - Power supply : The PSU (Power Supply Unit) receives the electricity from wall socket of main power supply, converts the alternating current (AC) to the low voltage direct current (DC) to operate the motherboard, processor, peripheral devices.
Some PSU can also supply a standby voltage, so that the computer can be powered off when goes to hibernate or given shut down command but actually it is not powered off and consuming electricity so powered back on by an event and allow a computer to be started remotely via Wake on LAN or Wake on Ring or logically via keyboard power on when motherboard supports it.
- Fan : is used to inhale the cool air from outside into the cabinet so the components stay safe from overheating and it also exhale the heated air from inside to the outside via heated sink.
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| Power supply and fan |
Optical Drive : This is the disc drive uses the laser light beam or electromagnetic waves in visible light spectrum as part of the process of reading or writing data to or from optical disc. Some drives can only read from the certain disc, but mostly can read and record (write) both on the optical disc. These are called burners or writers disc. Examples are CD, DVD, Blue Ray Disc. |
| Optical Drive |
- Hard Disk Drive : A Hard disk drive is an electro-mechanical data storage medium that stores and retrieve digital data. It is composed of rigid, rapidly rotating platters made up of aluminium or glasses coated with magnetic material. Platters having compartments to hold data. Here magnetic heads are arranged on a moving actuator arm. These heads are used to read and write data on the surface of the platter by moving of the actuator arm. The platters and actuator are delicate so covered under steel case to prevent damage to the disk under normal circumstances.
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| Hard Disk Drive |
A hard disk can store operating system, other system and application programs, all files/folders. It has large storage capacity, can store data up to 20 TB.
- Motherboard : A mother board is a Printed Circuit Board which provide connectivity between all he hardware components of the system, like CPU, RAM, Hard drive etc. It holds and allow the communications between many of the crucial electronic components of the computer. It is also called mainboard, MB, mboard etc
There are different types of motherboard designed to fit with different types and sizes of the computers. For each kinds of computer the motherboard is designed differently according to its processor and memory.
Expansion Slots : An expansion slot is used to attach an adapter to the motherboard.
There are rules to control the number of bits can be transferred at a time to the adaptor. An adapter allows connecting a peripheral device with one plug to different jack on the computer.
Connectors : There are many kinds of connectors found to attach different peripherals to the CPU.
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Connectors
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AC Power : Connects CPU to the main power AC supply.Mic/Line Input/Speaker Output : Used to connect microphone and speaker respectively to record or listen to the sound. The mic line input comes in 3 poles and 4 poles. 4 poles supports an extra microphone on the earphone or headphone.
USB : Used to connect keyboard, mouse, printer, digital camera, pen drive etc Serial : It is found in old type of PC, it allows to transfer one bit data at once. Usually used to connect printer or other peripherals. |
| Serial Connector |
eSATA : Used to connect external storage device. External storage device may connect with computer either by USB port or eSATA port. |
| eSATA Connector |
Parallel Connector : Used to connect a printer. It allows a computer to receive or transmit data down multiple bundled cables to aperipheral such as printer.  |
| Parallel Connector |
Displayport : It is a digital display interface unit used to connect computer with monitor. It can also carry audio, USB and other forms of data. |
| Displayport Connector |
3. Output Devices : Output devices shows the result of the work done by the computer. The most commonly used output device are monitor and printer.Let us study some most common output devices along with monitor and printer.
Monitor : It displays the information after being processed on the screen, this kind of information which we can see on the screen in digital form is called soft copy.
There are different types of monitors, like CRT, LCD and LED..
i. CRT : A CRT monitor is a specialised vacuum tube, having one or more electron guns which produce electron beams. This beam strikes a phosphorescent surface and forms an image.
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| CRT |
It consumes more electricity than those of other types and occupies large space on the table.
ii. LCD : It replaced the traditional bulky, tube monitor. It is a flat panel display that uses the light modulating properties of liquid crystal combined with polarizers. A liquid crystal doesn't emit light directly, but uses a backlight or reflector to produce an image in colour or monochrome form.
iii. LED : A LED forms the image by Light Emitting Diode. Which are basically tiny bulbs. It is lighter and thin than one of the LCD. Consumes less electricity and picture quality is improved due to high contrast images are formed having continuous brightness. It does't produce the heat so more environment friendly than a CRT.
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| LED |
PRINTER : A printer is one of the peripherals used to display information of computer on paper by taking out print, what is on the screen on the paper. The information taken on the paper in physical form is called hard copy. The paper used here generally 8.5" by 11" in size, called A4 sheet. But other sizes of paper can also be used with different printers.There are many kinds of printer available according to its size, speed, sophistication etc.
Some of the printers are Dot matrix, Inkjet, Laser, 3D printers etc.
i. Dot matrix printer : It is an impact printer. It prints using a fixed number of pins or wires. These pins or wires are arranged in one or more columns. The pin strikes an ink coated ribbon and a force works between ribbon and the paper and a dot is printed by one pin. The combinations of such dots make a letter or a character on paper.  |
| Dot matrix printer |
ii. Inkjet Printer : It prints the digital image by spraying droplets of ink onto the paper.
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| Inkjet printer |
iii. Laser Printer : It produces high quality image of text or graphics on paper by passing a laser beam continuously around a drum which has negatively charged cylinder. The drum collects electrically charged powdered ink which is called toner and transfer the image onto paper. Which is then heated to permanently fuse the image with the paper. In this way high quality image of text or graphic formed.  |
| Laser Printer |
iv. 3D Printer : 3D printing also called AM (Additive Manufacturing) used to create three dimensional image layer by layer. It is an additive process whereby layers of material are built up to create 3D image.  |
3D printer
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Plotter : Used to take large print out on paper. It produces vector graphics drawing. It draws lines onto the paper using a pen or use a knife to cut the material like vinyl or leather.
Used to give the image more accurately used by architect, engineers for map, architectural image etc. |
| Plotter |
Projector : A computer projector projects an image onto a surface and displays Videos, images or computer data on large screen.  |
| Projector |
Speakers : Computer Speaker is used to listen to music and sounds or any audio file of a computer in higher (clear) pitch. |
| Speaker |
