The IBM PC was announced on 12 August 1981, and the first machines began shipping in October the same year, ahead of schedule. CP/M-86 was one of three operating systems available from IBM, with PC DOS and UCSD p-System. Digital Research's adaptation of CP/M-86 for the IBM PC was released six months after PC DOS in spring 1982, and porting applications from CP/M-80 to either operating system was about equally difficult. In November 1981, Digital Research also released a version for the proprietary IBM Displaywriter.