CRC errors

From: allisonp <allisonp_at_world.std.com>
Date: Thu Jul 6 19:12:49 2000

From: Tim Mann <mann_at_pa.dec.com>

>Of course, with floppy disks we have sectors of 128 to 1024 *bytes*, not
>bits, and the CRC is only 16 bits, not 32, so I don't think we can do
>much correction. With a 1024 byte sector, it already takes 13 bits of
>information to say where a 1-bit error is. So if we use a CRC16 to
correct
>it, we have about a 2^(-3) = 1/8 probability that if more than one bit
>is in error, we'll make a spurious correction.


Therein lies the difference, the use of CRC vs ECC, floppies have a
fairly
high soft error rate compared to hard errors so detecting an error and
rereading is the strategy. It is also an economy of design that comes
from the characteristic otherwise you can bet there would be ECC.

Allison
Received on Thu Jul 06 2000 - 19:12:49 BST