During the late 1970s and early 1980s, the Z80 was used in a great number of fairly anonymous business-oriented machines with the CP/M operating system, a combination that dominated the market at the time. Four well-known examples of Z80 business computers running CP/M are the Heathkit H89, the portable Osborne 1, the Kaypro series, and the Epson QX-10. Less well-known was the expensive high-end Otrona Attache. Some systems used multi-tasking operating system software (like MP/M or Morrow's Micronix) to share the one processor between several concurrent users.