cdrecord and md5sum of the CD and of iso image

["H.S." <hs.samix@gmail.com>]

If I use the "-dao" option while buring a CD using cdrecord, I get a
md5sum match between the iso I burned and the CD device:
$> cdrecord blank=fast -v -eject  -dao dev=/dev/hdd data.iso

However, if I do not use the "-dao" option, the md5sum of /dev/hdd and
the iso image do not match, moreover, "md5sum /dev/hdd" actually
terminates with an I/O error.

Then I came upon this page which explains the -pad and padsize options:
http://www.troubleshooters.com/linux/coasterless.htm

It appears that using "-pad padsize=63s" works partially, since even
though I get an md5sum from the /dev/hdd device, but it doesn't match
the iso I burned:
$> cdrecord -v -eject padsize=63s -pad -dao dev=/dev/hdd data.iso

Apparently, using -pad and padsize is supposed to give a more
universally readable CD.

Can somebody shed some more light on this? I am not familiar with the
pad options. Why do they change the md5sum of the CD? And would the CD
still work? So far, just -dao has worked perfectly for me. Any other
information regarding this is also appreciated.

regards,
->HS