[TUHS] Question about BSD disklabel history

Bakul Shah bakul at iitbombay.org
Mon Jan 1 10:13:02 AEST 2024

On Dec 31, 2023, at 12:07 PM, Warner Losh <imp at bsdimp.com> wrote:
> Yes. Unlike today, the partitions covered the disk in different, overlapping
> ways. And allowed for some parts of the disk to be uncovered by a
> partition. You could then patch the offset and length into the kernel with
> adb and use that area of the disk for swap space.
>> It was also helpful, if you had the drives, to nightly dd
>> your real root to the "a" partition on another, identical
>> drive, so that you could boot the backup root in an emergency.
>> I don't remember for sure, but I think that Ultrix may have
>> been the first BSD-style system to have disk labels, followed
>> by some version of SunOS. All of that is way in the distant
>> past though: mid- to late 80's.
> When I looked into it years ago, I convinced myself that SunOS
> was the first to have it (since the very first version of SunOS 1.0
> had disk labels) and that all the other vendors followed suit within
> a couple of years. Ultrix-11 had the fixed labels through its EOL.
> I didn't see any disklable stuff in the Ultrix-32M that we have, but
> it was admittedly a quick look.

I wrote the first 2-3 HD drivers for Fortune Systems. I had
the first one up and running[1] by late 1981. IIRC we used an
ioctl to read/write sector 0 of a disk, which is where we
stored partition info. I think by 1983 we were using some
4.1a bits (or at least influenced by it) so likely disklabel
was used by then. The first disk drive was 5MB and cost
$1700. But 5 1/4" disk capacities were growing fast so there
was no question of hardwiring a disktab in source code. I
even had a program that would try to "step" through cylinders
until it ran into errors, to find at usable capacity!

[1] Well, more like walking! Initially DMA didn't work on the
first wirewrap boards so had to use PIO (programmed IO),
at 25KB/s. A quick hack doubled that performance, while
an ST506 disk could do 5Mbits/sec.
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