There are few categories of computers : - Personal computers, Mobile computers and devices, Game consoles, Servers, Mainframes, Supercomputers and Embedded computers.

• Personal Computers - can perform all of its output, processing, input, and storage activities. Two popular architectures are the PC and the Apple

• Mobile Computer - can carry to anywhere. Examples include notebook computers, laptop computers, netbooks, ultra-thins, and Table PCs.
  
• Mobile Device - the size of your hand. Examples are smart phones, PDAs, ebook readers, handheld computers, portable media players, and digital cameras.
  
• Game Consoles - is a mobile computing device designed for multiplayer or single player video games.
  
• Servers - a server controls access to the hardware, software, and other resources on a network. (Provides a centralized storage area for programs, data, and information)
  
• Mainframes - a very large, expensive, powerful computer that can handle hundreds and thousands of connected users simultaneously.
  
• Supercomputers - the fastest, most powerful computer. They are capable of processing more than one quadrillion instructions in a single second.
  

Embedded Computers - is a system with a dedicated function within a larger mechanical or electrical system, often with real time computing constraints.

Examples of Computer Usage : - Home User, Small office/Home office user, Mobile user, Power user, and Enterprise user.

• Home User - Communications, Entertainment, Web Access
• Small Office - Look up information, Send and receive e-mail messages, Make telephone calls
• Mobile User - Watch movies, Listen to music, Play video games, Transfer information
• Power User - Work with multimedia, Use industry-specific software
• Enterprise User - Communicate among employees, Blog

Computer Applications in Society : -  Education, Finance, Government, Health Care, Science, Publishing, Travel, Manufacturing.