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22 Mar 2017

Multics Simulator

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The Multics CPU simulator created by Harry Reed and Charles Anthony is available for public download. A complete QuickStart installation package is available that provides software, compilers, system source, install scripts, and several initial projects (SysDaemon, SysAdmin, Daemon, etc.) and users.

How to Install and Run a Simulated Multics

Eric Swenson has written a useful Wiki document on how to build a Multics simulator and install your own Multics, on a Mac OS X, Linux, or Windows machine, running on Intel (32 or 64 bit) or Raspberry Pi hardware. The current simulator is not yet a final 1.0 release, so early adopters may find some rough edges.

What It Can Do

Simulated Multics is a complete multi-user operating system, running on a simulated Honeywell DPS8M processor.

A community of developers has contributed bug fixes and enhancements to Multics beyond the last version released by Bull. The operating system and commands have been modified to support dates in the 21st century. Several shared systems have provided stable service for months, shutting down only to install new releases.


Harry Reed started a project in 2012 to create a software simulator for the Multics 6180 CPU based on Bob Supnik's SIMH. With major assistance from Charles Anthony, the simulator booted Multics on Saturday 08 November 2014. It has continued to improve since then, with contributions from several other Multicians, including Gary Dixon, Eric Swenson, and Daiyu Hurst.

Prior Multics simulator projects such as Michael Mondy's provided useful experience and learning.

At the ACSAC 30 conference in December 2014, Olin Sibert demonstrated simulated Multics to a distinguished audience. He started the simulator, booted Multics, wrote a little PL/I program, compiled it, and ran it. A panel of Multicians discussed "Multics: Before, During, After".


Stephen Jones of the Living Computer Museum in Seattle has posted a video on YouTube of a real 6180 maintenance panel booting the Multics simulator. The panel is connected to a Linux machine by a special board.

Stephen wrote me:

Charles Anthony modified the DPS-8/M emulator code to support the 6180. The panel was put on eBay several years ago and I purchased it. My understanding is that it came from University of Oakland. I believe all panels of that system were saved and nothing else. The interface between the emulator, which is running under Linux on intel i7, is serial to a BASYS3 Xilinx that in turn drives two logic boards attached to the panel's wiring harness. All lamps and switches are available to emulator and that includes the scrolls as well. Just about all displays can be achieved at this time (though maybe more later?). The emulator is booted via switches on the front panel set to 024000717200 followed by the initialize button.

The system boots up to idle in just under 2 minutes, which, from what I understand, is blazingly fast. We are reorganizing our 2nd floor exhibit and hope to develop this into an interesting display with an interactive terminal, as well as remote access, at some point in the next few months. We are also *very interested* in hosting Multicians to celebrate Multics sometime this year. More details regarding this to come and we're open to suggestions in terms of significant/convenient dates.

Multics on a Raspberry Pi

Vince Scarafino sent some nice photos of Multics running on his Raspberry Pi. The computer is about the size of a deck of cards. He wrote me:

[VFS] I have a Raspberry Pi 2, which has a 900 MHz 32-bit quad-core ARM A7 processor. It has one gigabyte of memory, so the simulator, which uses 270 megabytes of memory, doesn't page. The file system is located on a MicroSD card. My current Linux system has six gigabytes cofigured.

[VFS] It runs Multics at an approximate half a MIP speed: performance test results. It's probably close to the first Multics processors we got at Ford. When the simulator is able to support multi-threaded virtual processors, I should be able to configure a four processor Multics system and get increased throughput, since the A7 is quad-core. There is a Raspberry Pi 3 available, which has a 64-bit processor, but still comes with a 32-bit operating system. I suspect it provides better performance, but I have no specific information. (Running the simulator on my MacBook Pro creates a Multics machine with approximately 7 mips performance.)

Closeup of the computer. (click for a larger view)

The screen shows the Multics operators console in the upper right and a user login in the lower right. (click for a larger view)