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  From: David Lloyd <lloy0076@rebel.net.au>
  To  : Martin Stacey <martin@safcol.com.au>
  Date: Thu, 21 Dec 2000 20:57:55 +1030

Re: Formatting tapes?

Martin!

> > Is there a command to format a tape?
> 
> Modern tapes aren't formatted.

Given the multitude of meanings `formatting' a device has (blame
Windows), it may be pertinent to ask what do you mean by formatting the
tape? A reasonable explanation could be given by how the command dd can
work:

   bs=blocksize (in bytes)

Each discrete block, or chunk, will be this size

Using the count parameter you can get count number of blocksizes, so:
   
   [prompt]% dd if=/dev/nst0 of=tape.dd bs=64 count=1

gets 1 block of 64 bytes. This is the same as:

   [prompt]% dd if=/dev/nst0 of=tape.dd bs=32 count=2

(2*32=64)

What you are actually doing is getting streams of data from the tape and
placing it into a file called tape.dd. What you then _do_ with that data
is up to you.

The corollary is that you write streams of data to the tape. Most of the
time programs will attempt to write to tape in blocks rather than one
byte/bit at a time. It's much more efficient. But at the end of the day,
the tape is just a series of magnetic ons and offs and their format
doesn't matter.

Therefore, as Glen has already pointed out, the tapes themselves are not
formatted. However there are conventions that O/S use such as the tape
label and so forth to organise tapes in a more efficient manner...

DL
-- 
GOD SAVE AMERICA!
 - because President Bush, the Second Will Not!

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