There are four main types of computers: mainframes, supercomputers, professional workstations, and personal computers. Mainframes were the first computers used by businesses in the 1950s and are very large, expensive machines that allow thousands of users to access information simultaneously. Supercomputers are even more powerful than mainframes and can process trillions of calculations per second, used by research facilities. Professional workstations have more power than personal computers but less than mainframes, used by scientists and designers. Personal computers began with the Apple I in 1976 and are now used by almost all individuals and businesses.