Answer:
There is no such thing as "PC OS." The IBM PC and compatibles are host to a variety of operating systems, including MS-DOS, Windows, Linux, OS/2, FreeBSD, NetBSD, OpenBSD, Solaris, BeOS, SkyOS, Syllable, CP/M, DR-DOS, FreeDOS, SCO Unix, AROS, KollibriOS, Haiku, Native Oberon, Minix, MenuetOS, QNX, VisiCorp Visi On, and probably a dozen more I probably forgot.