[Simh] Adding storage to vax running 4.3BSD

[Johnny Billquist]

On 2017-05-11 22:52, Clem Cole wrote:
>
> On Thu, May 11, 2017 at 4:37 PM, Johnny Billquist <bqt at softjar.se
> <mailto:bqt at softjar.se>> wrote:
>
>     True. However, it isn't actually the geometry that cause the Unix
>     messup here, but the fact that Unix divided disks into partitions.
>     So it needed to know where each partition started. And before
>     disklabels, it was hardcoded per disk type.
>
> ​To be fair....

Well...

> UNIX partition the RP06 because it overflowed a 16bit integer on the
> PDP-11.    The 36 bits machines DEC was making at the same time did have
> that problem.    Because UNIX supported mounted file systems which most
> small computer systems could not, ​it was a fairly elegant solution.

The DEC OSes did not suffer this problem (or rather, some of them 
didn't, RT-11 do have this limitation). Just because the word size of 
the PDP-11 is 16 bits you did not have to limit the size of a file 
system to 16 bit block numbers. And in the DEC OSes, mounted file 
systems were something available to all, and not just privileged 
users... (And yes, you did need to mount file systems.) Are you making a 
comparison to systems like CP/M?

Not sure I understand the 36-bit comment, unless it was a typo for 16 
bits...

Also, with 16 bits, the maximum size of a disk would be 32M, which you 
hit already with the RP04 or RM03. RP06 is massively larger than that, 
at 167M.

> Like many software tricks that were introduced to solve one issue, it
> was a handy solution for others and partitions became de rigor for
> quotas, organization and other sins.   The commercial UNIX vendors put
> labels and support in the disk ROMS pretty early, (PC/UNIX's was ham
> strung by the sins of IBM) but its a classic example of things are the
> way there are because it made a lot of sense when it was done.   Time
> moved on....

True in its way, but at the same time not everyone was doing it, so the 
excuse that such were the times are a pretty weak argument.

> And as Paul and I were discussing off-line 'support' for MSCP really was
> not a 'mess-up' -- it was a zip/zag where DEC went one direction and by
> that time it came out, BSD was trying to solve a problem different than
> what DEC's cared about and non-DEC UNIX vendors started having their own
> solution.
>
> So while its an example of the start of DEC HW being to quit being the
> 'focus' for things UNIX.  It was a cool new thing DEC had, but
> basically it was minimally supported, not exploited, because people did
> not care at the point.

Well, MSCP was a good solution, and it's rather funny to now watch SATA 
and SAS, which is almost a carbon copy of MSCP and DSI, but 20 years later.

But I think it's mostly a red herring talking about MSCP while on this 
subject. MSCP was trying to solve one problem. The partition table thing 
in Unix was for addressing a different problem, so MSCP or not don't 
really matter here.

Once you had the partition tables, you had a problem with unknown disks, 
no matter what the controller and interface to the disks look like.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol