A very large and expensive computer capable of supporting hundreds, or even thousands, of computer users simultaneously. In the hierarchy of computing power, with simple microprocessors at the bottom (the kind found in watches, for example) and supercomputers at the top, mainframes are just below supercomputers. Supercomputers can execute a single program faster than a mainframe, but in a sense, mainframes are more powerful since they can support more simultaneous programs. The distinction between "small mainframes" and minicomputers is vague, mostly depending on how the manufacturer is marketing its machines. Unisys and IBM are the largest manufacturers of mainframes.