MMU support for 286 class machines was provided using a proprietary hardware shim inserted between the processor and its socket.
Multi-user operation suffered from the limitations of the day including the inability of the processor to schedule and partition running processes. Typically swapping from a foreground to a background process on the same terminal used the keyboard to generate an interrupt and then swap the processes. The cost of RAM (over USD$500/Mb in 1987) and the slow and expensive hard disks of the day limited performance.
PC/MOS terminals could be x86 computers running terminal emulation software communicating at 9600 or 19200 baud, connected via serial cables. Speeds above this required specialist hardware boards which increased cost, but the speed was not a serious limitation for interacting with text-based programs.
PC/MOS also figured prominently in the lawsuit Arizona Retail Systems, Inc. v. The Software Link, Inc., where Arizona Retail Systems claimed The Software Link violated implied warranties on PC/MOS. The case is notable because The Software Link argued that it had disclaimed the implied warranties via a license agreement on the software's shrinkwrap licensing. The result of the case, which Arizona Retail Systems won, helped to establish US legal precedent regarding the enforceability of shrinkwrap licenses.