1. The document discusses the characteristics of computers including what computers can do like store large amounts of information and perform tasks quickly and what they cannot do like work without electricity or instructions.
2. It describes different types of computers based on size from largest to smallest: supercomputers, mainframe computers, minicomputers, and microcomputers which include personal computers.
3. Computers are also classified based on their purpose as either general-purpose computers that can be used for any task or special-purpose computers designed for specific tasks.