Minicomputers have a unique architecture that distinguishes PCs from their servers, as well as proprietary technologies of various manufacturers, and some also use minicomputer-specific processors. For example, the minicomputers of Sun Company of the United States and Fujitsu Company of Japan are based on SPARC processor architecture, while the minicomputers of Hewlett-Packard Company of the United States are based on PA-RISC architecture. Compaq is an Alpha architecture. In addition, I/O buses are different, Fujitsu is PCI, Sun is, and so on. This means that plug-in cards on small computers of various companies, such as network cards, graphics cards and SCSI cards, may also be dedicated. In addition, minicomputers generally use Unix-based operating systems, such as Sun Solaris for Sun and Fujitsu, HP -UX for HP, and AIX for IBM. Therefore, minicomputer is a closed special computer system. Users who use minicomputers generally value the security and reliability of Unix operating system and the high-speed computing ability of dedicated servers.