Mach ’86 on the SIMH VAX

Kernel booting from 1986

While the kernel may boot on SIMH there is certainly something going on with the SIMH emulation of the hardware that threw me for a few loops. I had a pre-installed version of 4.3BSD which was on a RA81 disk but shortly after loading the kernel various binaries wouldn’t load, filesystems wouldn’t mount and of course the inevitable file corruption.

This led me to the fun of loading up 4.3 onto RP06 disks as they are smaller and I was hoping less prone to errors. During this fun, I found this page on plover.net, which as a fun filled tangent shows how to use the Quasijarus console floppy image to run the standalone programs. With the latest version of SIMH, I can run format and it initializes the disks, so I almost think it may be possible to do some kind of ‘native install’ on the VAX-11/780 SIMH, although It’s not what I was in the mood for.

So finally with an install over several RP06 disks, I was lucky enough to figure out how to build the Mach’86 kernel, and get it to boot, and then the corruption happened again. Luckily for me I had snapshotted the disks before experimenting and noticed how even those had issues booting up. It’s after a bit of searching I found that other people may have issues with SIMH’s Async I/O code, and the best thing to do, is just to disable it with a “set noasync”.

Now my disks could boot under the Mach kernel, and I could self host!

self hosted!

Setting up the build involved copying files from the ‘cs’ directory to their respective homes, along with the ‘mach/bin/m*’ commands to the /bin directory. Configuring the kernel is very much like a standard BSD kernel config, however the directory needs to exist beforehand, and instead of the in path config command run the config command in the local directory.

While maybe not perfect, keep in mind I haven’t found any real instructions as of yet, so this is more of a ‘wow it booted’ kind of thing at the moment.

While this kernel does have mentions of multi processor support I haven’t quite figured out what models (if any) are supported On the VAX, and if SIMH emulates them. While oboguev.net has a very interesting looking multiprocessor VAX emulation, VAX_MP it’s a fictional model based on the microvax, which I’m pretty sure 4.3BSD/Mach’86 is far too old for.

And for those who want to play along, here is a zip file of the disk images, emulator and config file I’m using, Mach86.zip

Author: neozeed

I live in SE Asia, doing generic work, enjoying my life & family

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