February 17, 2018 UPDATE

Thanks to Amazon.com, my Mach386 development system is working again.
After ordering 40 1000uf 6.3v electrolytic capacitors from them at
11:30pm last night, they arrived at 12:00 (noon) today. 12 hours and
30 minutes after ordering, and another two hours replacing all 24
capacitors on the motherboard, and it is working solidly again.

I took my time on the capacitor replacement. I replaced three to four
at a time, and tested the motherboard at each interval. The motherboard
came alive again after the second set, which was a group of capacitors
just along the Slot-1 CPU itself. I continued replacing all the capacitors
in groups ensuring that, had I made any mistakes soldering, it would
be easy to locate and resolve. I did not have to rework any replacements
or otherwise make corrections on the board.

While I was awaiting the board repair, I began trying to understand and
document how to install Mach386 to a disk, or add a new disk drive to an
existing Mach386 system, which is greater than 4GB. There are a number
of issues with large drives and this older UNIX operating system. The
issues exist not only for IDE/ATA drives but the same problems exist for
SCSI drives.

The fundamental problem is that while Mach386 disk drivers will happily
use whatever configuration they're told, they obtain the disk geometry
from a Mach VTOC stored on the drive. To get this VTOC created, one
must use a combination of the utilities fdisk(8), badblocks(8), vtoc(8)
and diskutil(8) to get a drive set-up for Mach to use. The trick lies
in getting a working VTOC written with a geometry different than what
BIOS or the device itself has reported.

The Mach386 kernel drivers are not able to readjust a disk's geometry
dynamically. So there are a number of reboots that must occur. In
particular, immediately after changing the geometry for the fdisk
partition, the VTOC partition and then again after generating the Mach

Mach partitions are very similar to disklabel(8) partitioning and while
reported by disklabel(8), are not the same. The earlier (pre-March 1992)
Mach386 systems did not use VTOC. VTOC was introduced after that time
both in floppy distributions as well as sysload(8)/online updates. Once
VTOCs are employed, the disklabel(8) facility should not be used and
will even cause problems if partitioning is changed via disklabel(8).

I did manage to add an additional ATA 10GB drive today and partition, format
and copy filesystems from a SCSI disk. This was, however, not easy
and very time consuming primarily due to the empirical learning and under-
standing of the process to change geometries to within the 4GB limit.
I plan to continue determining how to best perform this process and
will document it.

I really wish I could find Mach 2.6MSD sources, especially to these
disk utilities.