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FreeBee - AT&T 3B1 emulator

FreeBee is an emulator for the AT&T 3B1. It's a work-in-progress, but currently works well enough to boot the operating system and to compile programs with the standard C compiler.

Maintained by

Phil Pemberton --


There are a number of known instability issues with the Apple Mac OS. I'm bored of trying to work around these issues, for a platform I don't use.

If you have an issue on OSX, first try to reproduce it under a Windows or Linux build. If you can, report it as an issue under one of those platforms.

I will not accept pull requests or issues which have been reported solely on an Apple system or Mac OS.

Things which are emulated...

  • Revision P5.1 motherboard with 68010 processor, WD2010 hard drive controller and P5.1 upgrade.
  • 720x348 pixel monochrome bitmapped graphics.
  • 4MB RAM (2MB on the motherboard, 2MB on expansion cards).
    • This is the maximum allowed by the memory mapper.
  • Keyboard and mouse.
  • WD2010 MFM Winchester hard disk controller.
    • Two separate drives.
    • Maximum 1400 cylinders (limited by the UNIX OS, see the UNIX PC FAQ, section 5.6).
    • Heads fixed at 8.
    • Sectors per track fixed at 17.
    • Fixed 512 bytes per sector.
    • Those numbers are the default configuration; see below for more information.
  • WD2797 floppy disk controller.
    • Double-sided, 512 bytes per sector, 10 sectors per track, any number of tracks.
  • Realtime clock.
    • Reading the RTC reads the date and time from the host.
    • Year is fixed at 1987 due to Y2K issues in the UNIX PC Kernel.
  • Serial port.
    • Linux only: file 'serial-pty' is symlinked to PTY that can be used to access tty000
    • Usage instructions:

Things which aren't emulated fully (or at all)

  • Printer port
  • Modem
    • You will get errors that '/dev/ph0 cannot be opened' and that there was a problem with the modem. Ignore these.

Build instructions

  • Install the libsdl2-dev package
  • Clone a copy of Freebee (remember to check out the submodules too)
    • git clone --recurse-submodules
  • Build Freebee (run 'make')

Running Freebee

Initial Setup

  • Download the 3B1 ROMs from Bitsavers: link
  • Unzip the ROMs ZIP file and put the ROMs in a directory called roms:
    • Rename 14C 72-00616.bin to 14c.bin
    • Rename 15C 72-00617.bin to 15c.bin

Option 1: Use an existing drive image

  • Arnold Robbins created a drive image installed with all sorts of tools: here
  • David Gesswein created a drive image for the VCF Museum: here
  • Uncompress either of these images in the Freebee directory and rename the image to hd.img, or create a .freebee.toml file pointing to the image. (See the CONFIGURATION section of the man page.)

Option 2: Do a fresh install

  • Download the 3B1 Foundation disk set from Bitsavers: here
    • The disk images on don't work: the boot track is missing.
    • Use the replacement version of the 08_Foundation_Set_Ver_3.51.IMD image which is available here.
  • Create a hard drive image file:
    • Use the makehdimg program supplied in the tools directory to create an initial hd.img file with the number of cylinders, heads and sectors per track that you want. Limits: 1400 cylinders, 16 heads, 17 sectors per track.
    • When using the diagnostics disk to initialize the hard disk, select "Other" and supply the correct values that correspond to the numbers used with makehdimg.
    • Alternatively, you can use dd if=/dev/zero of=hd.img bs=512 count=$(expr 17 \* 8 \* 1024) to create a disk matching the compiled-in defaults. Initialize the disk using the "Miniscribe 64MB" (CHS 1024:8:17, 512 bytes per sector) choice.
    • The second hard drive file is optional. If present, it should be called hd2.img. You can copy an existing hd.img to hd2.img as a quick way to get a disk with a filesystem already on it. When Unix is up and running, use mount /dev/fp012 /mnt to mount the second drive. You may want to run fsck on it first, just to be safe.
  • You can also use the ICUS Enhanced Diagnostics disk. A bootable copy is available here. Uncompress it before using.
  • Install the operating system:
    • Follow the instructions in the 3B1 Software Installation Guide to install UNIX.
    • Copy 01_Diagnostic_Disk_Ver_3.51.IMD to floppy.img in the Freebee directory.
    • If you wish to increase the swap space size, do so with the diagnostics disk before installing the OS. See these instructions.
    • To change disks:
      • Press F11 to release the disk image.
      • Copy the next disk image to floppy.img in the Freebee directory.
      • Press F11 to load the disk image.
    • Instead of 08_Foundation_Set_Ver_3.51.IMD use 08_Foundation_Set_Ver_3.51_no_phinit.IMD from here. This will allow the emulated Unix PC to come all the way up to a login prompt after the installation.

Importing files

  • Files can be imported using the 3b1 msdos command which allows reading a 360k MS-DOS floppy image.
    • Use dosbox to copy files to a DOS disk image named floppy.img. This image must be in the same directory as the Freebee executable (or path specified in the .freebee.toml config file).
    • If the floppy.img file wasn't present on boot or was updated, hit F11 to load/unload the floppy image.
    • Run msdos from the 3b1 command prompt, grab the mouse cursor with F10 if you haven't already, then COPY files to the hard drive.
  • Another option is to use the s4tools here which allow you to export the file system image out of the disk image and import the fs image back. In particular, there is an updated sysv Linux kernel module which allows mounting the fs image as a usable filesystem under Linux.

Scaling the display

You can scale the display by setting scale factors in the .freebee.toml file. Scale values must be greater than zero and less than or equal to 45. This facility is useful on large displays.

Keyboard commands

  • F10 -- Grab/Release mouse cursor
  • F11 -- Load/Unload floppy disk image (floppy.img)
  • Alt-F12 -- Exit

3b1-specific key mappings

  • F1-F8 -- "soft keys" at bottom of screen
  • F9 -- SUSPD key (brings up list of windows)
  • Alt-Esc -- EXIT key
  • Alt-Backspace -- CANCL key
  • Page Up -- HELP key
  • Page Down -- PAGE key
  • Insert -- CMD key
  • Enter -- RETURN key
  • Alt-Enter -- ENTER key
  • Pause Break -- RESET BREAK key

Useful links

Other Notes

  • To make an MS-DOS disk under Linux (9 tracks per sector):

    dd if=/dev/zero of=dos.img bs=1k count=360
    /sbin/mkfs.fat dos.img
    sudo mount -o loop -t msdos dos.img /mnt
    ... copy files to /mnt ...
    sudo umount /mnt

  • To make a 10 track per sector disk image, just use count=400 in the dd command and then format the disk under Unix with iv and mkfs.

  • See this part of the FAQ on setting up multiple login windows.


FreeBee - AT&T 3B1 / 7300 UNIX PC emulator








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