1. Types and Components of computer System

2. What is a computer?
A computer is, at its most basic, a machine which can take instructions, and perform computations based on those instructions. Computers range from the very small to the very large. Some are capable of doing millions of calculations in a single second, while others may take long periods of time to do even the most simple calculations. 

3. types
Based on Capacity, speed and reliability computers can be divided into the following categories of computers:
Super computer
Mainframe Computer
Minicomputer
Microcomputer

4. supercomputer
A supercomputer is a computer which performs at a rate of speed which is far above that of other computers.
The primary use for supercomputers is in scientific computing, which requires high-powered computers to perform complex calculations. Scientific organizations like NASA boast supercomputers the size of rooms for the purpose of performing calculations, rendering complex formulas, and performing other tasks which require a formidable amount of computer power. Some supercomputers have also been designed for very specific functions like cracking codes and playing chess; Deep Blue is a famous chess-playing supercomputer.

5. Mainframe Computer
These are computers used by large organizations like meteorological surveys and statistical institutes for performing bulk mathematical computations. They are core computers which are used for desktop functions of over one hundred people simultaneously. Since mainframes are usually the most important computers in a company’s computational arsenal, they are routinely protected by multiple layers of security and power backup, both internal and external.

6. Mini computers
The Mini computers are a less bulky version of the mainframe computers. In times past, the minicomputer was typically a standalone device that was ideal for use by small and mid-sized businesses who needed more power and memory than could be obtained with microcomputers, but did not have a need for the resources provided by mainframes. More recently, a minicomputer is thought of in terms of being a server that is part of a larger network.

7. The Microcomputer
These are the most frequently used computers better known by the name of “Personal computers”. This is the type of computer meant for public use. Other than Desktop Computer the choice ranges as follows:
Personal Digital Computer
Tablet PC
Towers
Work Stations
Laptops
Hand Held Computer

8. Desk top Computer
A desktop computer is a personal computer in a form intended for regular use at a single location, as opposed to a mobile laptop orportable computer. Early desktop computers are designed to lie flat on the desk, while modern towers stand upright. Most modern desktop computers have separate screens and keyboards.

9. Laptop
A laptop computer is a personal computer for mobile use.[1] A laptop has most of the same components as a desktop computer, including a display, a keyboard, a pointing device such as a touchpad (also known as a trackpad) and/or a pointing stick, and speakers into a single unit. A laptop is powered by mains electricity via an AC adapter, and can be used away from an outlet using a rechargeable battery. Laptops are also sometimes called notebook computers,  notebooks,  ultrabooks[2] or netbooks.

10. Net books
Netbooks are a category of small, lightweight, and inexpensive laptop computers.

11. PDA
A personal digital assistant (PDA), also known as a palmtop computer, or personal data assistant,[ is a mobile device that functions as apersonal information manager. PDAs are largely considered obsolete with the widespread adoption of smartphones. In fact smartphones are PDAs, and it's just a name change. The difference is that not every PDA(especially old) can be called smartphone, because "phone" means calling and request of some network(e.g. gsm) access. [5]