Computers are classified into four main groups based on their processing speed, memory size, and price: supercomputers, mainframe computers, minicomputers, and microcomputers. Supercomputers are the most powerful but most expensive, used for complex tasks like weather forecasting. Mainframe computers are large-scale systems that can support thousands of users but require specialized facilities. Minicomputers have lower performance than mainframes but higher than microcomputers, and are used widely in business and government. Microcomputers, also known as personal computers, are the smallest and least expensive, widely used for desktop and laptop systems.