The term PC acronym refers to the abbreviations used for various computer-related terms. The most common acronyms are MSDOS (5 letters), DOS (3 letters), and ROM (3 letters). MSDOS stands for Microsoft Disk Operating System, which is an operating system developed by Microsoft for IBM compatible computers. DOS stands for Disk Operating System, which is a type of operating system that uses a disk drive to store data and programs. ROM stands for Read-Only Memory, which is a type of memory that can only be read from and not written to.