Re: Disks w/non-512-byte sectors?

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Mon, 2 Feb 2015 19:52:58 -0800
    From:        John Nemeth <jnemeth%cue.bc.ca@localhost>
    Message-ID:  <201502030352.t133qwMw009260%server.CornerstoneService.ca@localhost>

  |      Uh, starting at sector 63, has nothing to do with floppies.

Actually it does, I believe - just not directly.   The filesystem (from
floppy days, which in the early days, was the only disc type device usually)
typically started after the first track, which was reserved for boot info.
Why it was always one track I am not sure - particularly on floppy based media,
but it was probably a hangover from people more used to SMD (and similar)
discs, where track alignment (and cylinder) made more sense.

That convention just persisted - eventually discs got large enough that the
only way to represent something close to their capacity, using C/H/S
representation was to pretend there were 63 sectors/track (the biggest
value for the available 6 bit field).

Even though this no longer had anything at all to do with actual tracks, or
cylinders, the code that set the default place for the filesystem to start
continued placing it at the end of the first "track" - ie: starting at
sector 63.

So, it really does all originate with floppies - just like many other things,
it is (was) one of those things that was just kept alive through inertia,
because it didn't actively break anything.

kre