PC-MOS/386

{{Infobox OS

| name = PC-MOS/386

| logo =

| screenshot = PC-MOS-386 boot screen.jpg

| caption=A screen-print of the PC-MOS-386 startup screen

| developer = The Software Link

| source_model = Open source

| kernel_type = Monolithic

| supported_platforms = x86 architecture

| influenced_by = MS-DOS

| ui = Command-line interface (COMMAND.COM)

| family = DOS

| released = {{Start date and age|1987}}

| latest_release_version = 5.01

| latest_release_date =

| latest_test_date =

| marketing_target =

| programmed_in = 80x86 assembly language, C

| prog_language =

| language = English

| updatemodel =

| package_manager =

| working_state = Active

| license = GPL-3.0-only

| website = [https://github.com/roelandjansen/pcmos386v501 Github]

}}

PC-MOS/386 is a multi-user, multitasking computer operating system produced by The Software Link (TSL), announced at COMDEX in November 1986 for February 1987 release.{{Cite magazine |last=Lach |first=Eric |date=November 17, 1986 |title=Multiuser Operating System to Use 386 Microprocessor's Virtual Modes |url=https://books.google.com/books?id=izwEAAAAMBAJ&pg=PA15 |access-date=1 May 2025 |magazine=InfoWorld |publisher=Popular Computing, Inc. |pages=15 |volume=8 |issue=46 |issn=0199-6649}} PC-MOS/386, a successor to PC-MOS, can run many MS-DOS programs 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. PC-MOS/386 used to be proprietary, but it was released as open-source software in 2017.{{Cite news |last=Vaughan-Nichols |first=Steven |date=23 October 2017 |title=MS-DOS variant PC-MOS/386 reborn as open source |url=https://www.zdnet.com/article/ms-dos-variant-pc-mos386-reborn-as-open-source/ |access-date=1 May 2025 |work=ZDNET}}

History

The last commercial 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 earlier 8086 and 8088 processors.{{Citation needed|date=May 2025}} MMU support for 286-class machines was provided using a proprietary hardware shim inserted between the processor and its socket. 386 machines did not require any special hardware.

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.{{Citation needed|date=May 2025}}

PC-MOS used "dumb" terminals, referred to within MOS as 'workstations', connected to the machine running the operating system via serial ports communicating at 9600, 19200 or 38400 baud. Either dedicated terminals or computers running terminal emulation software could be used. All processing was done by the PC-MOS machine. Terminals running at higher speeds required specialized hardware boards which increased cost, but the speed was not a serious limitation for interacting with the text-based programs predominantly used under MS-DOS.{{Citation needed|date=May 2025}}

PC-MOS 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.{{Cite court|litigants=ARIZONA RETAIL SYSTEMS, INC. v. THE SOFTWARE LINK, INC.|vol=831|reporter=F. Supp.|opinion=CIV 91-1553 PHX RCB|court=United States District Court for the District of Arizona|date=July 27, 1993|url=https://cyber.harvard.edu/property00/alternatives/arizona.html}}

There was a year 2000 problem-like error in this operating system, first manifesting on 1 August 2012 rather than 1 January 2000; files created on the system after this date would no longer work.

On 21 July 2017 PCMOS/386 was relicensed under GPL v3 and its source code uploaded to GitHub,{{cite web|url=https://github.com/roelandjansen/pcmos386v501|title=pcmos386v501: PC-MOS/386 v5.01 final release including cdrom driver sources|first=Roeland|last=Jansen|date=8 February 2018|via=GitHub}} with the "year 2012" issue corrected.{{cite web |last=Sprinkle |first=James |date=30 January 2019 |title=files created after 20120731 seem to fail acc. wiki |url=https://github.com/roelandjansen/pcmos386v501/issues/2#issuecomment-459088430 |access-date=1 May 2025 |via=GitHub}}

Commands

Commands supported by PC-MOS Version 4 are:{{Cite manual |url=https://github.com/roelandjansen/pcmos386v501/blob/master/DOCS/v4/PCMOSv4UserManual.pdf |title=PC-MOS User Guide |publisher=PC-MOS |year=1991 |pages=23; 25; 31; 101–190; 207; 265–296}}