Do we still need ATA disk CHS addressing?

Warner Losh imp at
Mon Aug 10 18:57:27 UTC 2009

From: Dag-Erling Smørgrav <des at>
Subject: Re: Do we still need ATA disk CHS addressing?
Date: Mon, 10 Aug 2009 20:38:16 +0200

> "Julian H. Stacey" <jhs at> writes:
> > Alexander Motin <mav at> writes:
> > > Have anybody seen ATA drive without LBA support in last years?
> > Yes
> Have you really, or did you just assume that "old" means "no LBA"?
> > I run 20+ assorted hosts from 4.11 to 7.2 Uni & Dual proc, i386 (real 386!)
> > to 686 & amd64 so I guess I'm 
> >   A) Pretty vulnerable to legacy scare.
> >   B) A litmus tesst for a wider community of others, some  with older kit, 
> >      not on lists or with bleeding edge latest hardware, but will 
> >      get hit when stuff eg HCS gets declared legacy=dumped.
> Do you seriously intend to run FreeBSD 9 on kit that is too old to
> support LBA?  We're talking early nineties here.  CHS doesn't scale past
> 504 MB, so any ATA disk larger than that must peforce support LBA.  I
> bought my first 1 GB drive (Connor CFP1080) in 1995.

Is that also true in the pc98 realm?  There's a number of weird
combinations there which use CHS addressing, but that's kinda forced
onto it by weird pc98 disk label format.  I don't know if this is
required, and older stuff just won't work or not, but I do know that
there be dragons there.  I know, at the very least, that the system
requires that the CHS geometry reported by the drive be faithfully
preserved.  It is something we should ask nyan-san about at the very

As for the 'are you seriously going to run FreeBSD 9 on them'
argument, there's a rather large number of systems that people said
would be too slow to run FreeBSD 7 or 8, yet they are running them
better than anticipated.  They said that about many of the same
systems that Julian is running today.

My question, and maybe I missed this earlier in the thread, is what's
the benefit to removing this support?  How much code is saved?

Having said all that, I think it is OK, but I'd definitely poll the
pc98 guys first...  Just to make sure they don't need it and re-fork
the ata driver to get it :)


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