This website has moved! — Please go to AT&T 3B1 Emulator  

AT&T 3B1 Emulator

I'm currently working on an emulator for the AT&T 3B1 Unix PC. I haven't released any stable code yet, though the Mercurial repository is publicly-accessible. There are some documents and other items here which may be useful to 3B1 owners...

Thanks and acknowledgements

The 3B1 emulator would not be possible without the generous donation of two AT&T UNIX PC systems and software disks by Antoni Sawicki.

Andrew Warkentin has contributed many significant patches which improve the quality of the emulation and allow UNIX to be booted inside the emulator.

Mercurial repository

Moved to Bitbucket as of 2014-04-24.

Current status

(2014-04-24): Thanks to even more excellent work by Andrew Warkentin, FreeBee can now boot into UNIX (with a few errors along the way). Andrew's changes are on the "default" (OldMMU) branch and have yet to be migrated to the NewMMU branch.

(2013-03-13): Thanks to some sterling work by Andrew Warkentin, the emulator can now boot from the Foundation set and starts a shell. Unfortunately the OS fails to install, citing a "no stack" error. It seems like part of the memory mapping logic is broken, though debugging this would require physical hardware to test :(

(2011-02-10): The 3B1 emulator is capable of booting from the Diags disc, and will display the memory check screen. After hitting a key, you get the main menu, but PVTEST gets stuck there. No matter what option you pick (including s4test, i.e. Expert Mode), you just can't get to any of the submenus (the selection is echoed properly, but when you hit ENTER the screen clears and the main menu reappears). Something is obviously wrong with the keyboard driver...

(2010-12-05): I've got the Bootloader to boot from the Diagnostic disc on Bitsavers (converted from IMD to BIN format using the Imagedisk 'IMDU' tool):


Unfortunately the Loader seems to disregard the floppy drive and skips ahead to trying to boot from the hard drive. As I haven't emulated the HDD controller yet, this fails quite spectacularly. Evidently my WD2797 emulator is still a little broken.

Boot ROMs

  • AT&T 3B1 Boot ROMs / ROM set. Images (binary and Intel Hex) of the two 3B1 Boot ROMs. These are fitted at board locations 14C and 15C, and carry part numbers 72-00616 and 72-00617 respectively.

Technical documentation

Steven Hirsch scanned the entire of the two-binder AT&T 3B1 Unix PC Technical Reference, and released them on the Classic Computers Mailing List. With his permission, the scans are mirrored here:

UNIX PC Reference Manual

Circuit diagrams / schematics


System bus