A computer system is a nominally complete computer that includes the hardware, operating system (main software), and the means to use peripheral equipment needed and used for full or mostly full operation. Such systems may constitute personal computers (including desktop computers, portable computers, laptops, all-in-ones, and more), mainframe computers, minicomputers, servers, and workstations, among other classes of computing. The following is a list of notable manufacturers and sellers of computer systems, both present and past. There are currently 420 companies in this incomplete list.