Minix on Virtual PC: first look

modified: 2 Feb 2005

There have been several reports like this:

I tried to install Minix 2.0.3 under Virtual PC 2004 and received the error:
"File system panic: Cannot open RAM image device"

I've seen reports of problems like this with both the Windows and MacIntosh versions of VPC.

Apparently installation of Minix on Virtual PC using a native Minix file system fails because of the RAM disk problem. It is possible to install Minix without using a RAM disk, but I haven't received any reports of success in doing so on directly onto a Virtual PC virtual hard disk.

Several people have reported success with Minix on Virtual PC using DOSMinix, using either MS-DOS or FreeDOS(*). Gary Driggs <garyd@efn.org> has provided a VPC image for FreeDOS/DOSMinix 2.0.4. It is available at http://geek.eyetraxx.net/minix2.0.4.vhd.gz and also here at /pub/demos-2.0/VirtualPC/m204vpc-fd.gz. (The name has been changed because of the Minix 14 character filename length limit.)

Installation: The following applies to using on Virtual PC on a Windows platform. I assume VPC on a Mac is very similar, but I haven't had a chance to test it on a Mac myself(**).

If you download m204vpc-fd.gz to a Minix or other Unix-like system you can use gunzip to decompress it. Rename the resulting file as m204vpc-fd.vhd and then transfer it to the Windows or MacIntosh system on which you want to run Virtual PC. Or you can transfer the gzipped file directly to your Windows host and unzip it with Winzip or a compatible Windows archive/compression program.

I installed the trial version of Virtual PC by opening the downloaded VPC2004SP1Trial.zip from Microsoft and clicking on setup.exe. I made a default install on my Windows 2000 test system. Then I started VPC and used the New Virtual Machine Wizard. I named my new virtual machine Minix204FD. I selected the option to create a default virtual machine with no associated virtual hard disk, and when the Settings for New Virtual Machine window opened I changed the memory allocation from the default 101 MB to 40 MB, which is the allocation I usually used for Minix on other virtual or emulated systems, like Bochs and VMWare. (I later changed this to 32 MB, because VPC complained about there not being enough memory available when I started it.) I accepted default values for all the other settings. Then I closed Virtual PC. At this point the My Documents\My Virtual Machines\Minix204FD directory contained a Minix204FD.vmc virtual machine configuration file. I then used WinZip to extract minix2.0.4.vhd from the gzipped archive and moved this into the Minix204FD directory. Upon restarting Virtual PC I selected Settings, clicked on Hard Disk 1, and browsed to select the minix2.0.4.vhd vrtual hard disk. After closing the settings I clicked Start, and the emulated BIOS and then FreeDOS started, and then the AUTOEXEC.BAT started DOSMinix, presenting the familiar "Press = to start Minix" prompt.

Except as noted in the next paragraph, Minix worked well as far as I tested it. I found that I could set rootdev=ram in the boot monitor and run with the root on a RAMdisk, even though people who have tried to do a conventional installation of Minix onto a Virtual PC virtual disk have seen messages about inability to open the RAMdisk. I created a second virtual hard disk and was unable to format it with FreeDOS, but Minix was able to partition it and create file systems on the partitions, so this may be a route to making a true native Minix installation on Virtual PC. I recompiled the Minix system in a time that seemed normal for the PII-266 system I was using. I haven't checked out the floppy disk or CD-ROM interfaces yet, and I don't expect networking will work, since there is no Minix driver for the emulated DEC 21140 ethernet interface that Virtual PC presents to guest systems.

Problems: I had some problems with the keyboard interface while using Minix on FreeDOS on Virtual PC. Occasionally there would be long periods when Minix would not respond to keypresses, alternating with periods in which Minix acted as if the keys were bouncing, with multiple characters echoed for a single keypress. Caveat: my test system for the above installation was a 266 Mhz Pentium II, and Microsoft specifies a 400 Mhz system as a requirement for Virtual PC, so the problems I observed may not be seen on a faster system.

(*) About FreeDOS: FreeDOS is an open source substitute for MS-DOS. The FreeDOS home page is http://www.freedos.org/. FreeDOS is distributed under the Gnu General Public License. The GPL license is at http://www.fsf.org/copyleft/gpl.html. There is also a copy of the license in the FreeDOS C:\ETC directory on the virtual hard disk. To see it, you can try to abort the FreeDOS AUTOEXEC.BAT before it starts Minix or you can let Minix start, then exit from Minix and the Minix boot monitor to FreeDOS. (You might think that you could use mtools to read it from within Minix, but this doesn't work with this virtual hard disk.) FreeDOS is distributed here under the terms of section 3c of the GPL, which allows non-commercial redistribution accompanied with the information received as to the offer to distribute corresponding source code.

(**) Minix on VPC on MacIntosh: Gary Driggs wrote on comp.os.minix on Dec 1, 2004: I transferred my minix204.vhd to my Mac today. It's running Virtual PC for Mac ver 6.1. I've read in the MS newsgroup that 7.0 is a bit buggy and that 7.0.1 is due out this month. Anyhow, it recognized my .vhd and quickly converted it to a Mac VPC drive image and booted FreeDos and Dos Minix 2.0.4 w/o a hitch.