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PC-MOS-386 boot screen.jpg
A screen-print of the PC-MOS-386 startup screen
DeveloperThe Software Link
Written in80x86 assembly language c
Working stateDiscontinued
Source modelOpen-source
Initial release1987; 31 years ago (1987)
Latest release5.01
Available inEnglish
Platformsx86 architecture
Kernel typeMonolithic
Default user interfaceCommand-line interface
LicenseGNU GPL 3
Official websiteGithub

PC-MOS/386 was a multi-user, computer multitasking operating system produced by The Software Link (TSL), announced at COMDEX in November 1986 for February 1987 release.[1] PC-MOS/386, a successor to PC-MOS, can run many MS-DOS software titles on the host machine or a terminal connected to it. Unlike MS-DOS, PC-MOS/386 is optimized for the Intel 80386 processor; however early versions will run on any x86 computer.


The last version produced was v5.01, compatible with MS-DOS 5. It required a memory management unit (MMU) to support memory protection, so was not compatible with 8086 and 8088 processors.

MMU support for 286 class machines was provided using a proprietary hardware shim inserted between the processor and its socket. 386 machines didn't require any hardware changes.

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 US$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 specialized 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.[2]

It appears there is a Year 2000 problem-like issue in this product, only happening on 31 July 2012 rather than the year 2000. Files created on the system after this time will no longer work.[citation needed]

On 21st July 2017 it was relicensed under GPL v3 and its source code uploaded to GitHub.[3]

See also[edit]


  1. ^ Multiuser Operating System to Use 386 Microprocessor's Virtual Modes, InfoWorld, Nov 17, 1986
  2. ^ Bennett, Oliver. "Arizona Retail Systems". cyber.law.harvard.edu.
  3. ^ Jansen, Roeland (8 February 2018). "pcmos386v501: PC-MOS/386 v5.01 final release including cdrom driver sources" – via GitHub.