Accessing partitions in drive images

[Jon "maddog" Hall]

On Sun, 2012-01-29 at 16:34 -0500, michael miller wrote:
> The number of columns on a hollerith card.  Why are there 80 columns on
> a hollerith card?

Well, actually there were many different size "Hollerith cards", and
there were at least two sizes of "IBM cards", the familiar 80-column
card, and the smaller 96 column card.

Why 80 columns?  Probably a combination of having to have a hole large
enough that it could be accurately read at (relatively) high speed by
the sensing mechanisms of the day, yet still allow enough paper to be
existing on the card to give it structural integrity and to keep the
columns separate.  Some engineer was given the task of designing them.

Holes too small, sensors might miss the hole.  Holes too big, little
paper left for integrity.

The long-standing tale of the 80 column "IBM card" being that size was
due to a lot of cabinets and holders for dollar bills around, and the
"new" cards could be fit into those holders.

Then a few years later the government reduced the size of the dollar
bill, but by then there were probably more data cards in existence then
dollar bills, so the issue of getting manufacturers to make cabinets to
store the data cards was a non-issue.

md

> 
> Mike
> 
> On Sun, 2012-01-29 at 15:38 -0500, Ben Scott wrote:
> > On Sun, Jan 29, 2012 at 12:45 PM, Joshua Judson Rosen
> > <rozzin at geekspace.com> wrote:
> > > I've always wondered: why do the little USB flash sticks,
> > > SD cards, etc. all include a partition-table with one
> > > partition? Why don't they just use whole-device filesystems?
> > 
> >   Because they're not floppy disks, and fixed disks are assumed to
> > have a partition table.
> > 
> >   The design of the IBM-PC (I use the term "design" loosely) assumes
> > two types of disks: Floppy disks and fixed disks.  Floppy disks are
> > generally assumed to be of the few well-known types.  Fixed disks can
> > vary and one is expected to inquire as to the size.  Flash drives
> > wouldn't work as floppies, so they're treated as fixed disks.
> > 
> >   There's nothing insurmountable that keeps one from just putting a
> > filesystem on a USB flash drive.  Indeed, you can do it, and Linux
> > software will generally be just fine.  But it breaks a lot of
> > assumptions that could screw up BIOSes and other OSes, and/or lead to
> > those same things trying to write a partition table into your
> > filesystem.  And since your flash drive is technically laid out in a
> > non-standard manner (again, I use the term "standard" loosely), it
> > would arguably not be their fault.
> > 
> >   Next up: Why are console windows traditionally 80 columns wide?
> > 
> > -- Ben
> > _______________________________________________
> > gnhlug-discuss mailing list
> > gnhlug-discuss at mail.gnhlug.org
> > http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss/
> 
> _______________________________________________
> gnhlug-discuss mailing list
> gnhlug-discuss at mail.gnhlug.org
> http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss/
> 

-- 
Jon "maddog" Hall
Executive Director           Linux International(R)
email: maddog at li.org         80 Amherst St. 
Voice: +1.603.673.7875       Amherst, N.H. 03031-3032 U.S.A.
WWW: http://www.li.org

Board Member: Uniforum Association
Board Member Emeritus: USENIX Association (2000-2006)

(R)Linux is a registered trademark of Linus Torvalds in several
countries.
(R)Linux International is a registered trademark in the USA used
pursuant
   to a license from Linux Mark Institute, authorized licensor of Linus
   Torvalds, owner of the Linux trademark on a worldwide basis
(R)UNIX is a registered trademark of The Open Group in the USA and other
   countries.