: CD data recovery?

[Henry Spencer]

A low-tech :-) friend of mine asked me to inquire about this...

He's got a couple of CDs that are physically broken. (Shouldn't have put
them in checked baggage...) They're not mass-market items, and it would
be difficult to replace them without repeating some fairly expensive
travels. Anybody know of an outfit hereabouts that could recover their
contents, either as data files or as duplicate disks?

(These are music CDs, as it happens, but I've come close to needing this
once or twice for damaged CDROMs, and now he's got me curious too.)

Henry Spencer
henry-***@public.gmane.org

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[The Edge of the Ice]

On Mon, 20 Sep 2004 00:30:34 -0400 (EDT), Henry Spencer

Post by Henry Spencer
He's got a couple of CDs that are physically broken. (Shouldn't have put
them in checked baggage...) They're not mass-market items, and it would

If they're snapped, you may be SOL. If they're just scratched, I've
seen "restorative"
compound used to make a disc re-readable. It seems to work somewhat
like a cross
between a Zamboni and car wax: apply the cream, spread it around, let
it dry, polish it
off. It usually leaves the surface of the disc a bit milky, but that
doesn't seem to affect
the readability (or at least it tends to be much more readable after
than before).

[Henry Spencer]

He's got a couple of CDs that are physically broken...

If they're snapped, you may be SOL. If they're just scratched...

I haven't seen them, but my impression is multiple pieces, not just
scratches. Definitely a job for a specialist, not a do-it-yourself
project.

...seen "restorative" compound used to make a disc re-readable.

Yeah, surface scratches on the bottom can generally just be polished off.
Local defects on the bottom surface are not that bad, because the data
layer is just under the *top* of the disk, so the bottom surface is out of
focus to the reading laser.

Henry Spencer
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[Dave Bour]

Henry,
How badly are we talking. If single cracked, I've had success in
recovering portions of the data on it however, if it's two or more
separate pieces, you are likely SOL, though I can't say I've done that
to even say if it'd work or not. Drop a line off forum and we can talk.
D.


Dave Bour
Desktop Solution Center
905.381.0077
dcbour-***@public.gmane.org
http://www.desktopsolutioncenter.ca

-----Original Message-----
From: owner-tlug-***@public.gmane.org [mailto:owner-tlug-***@public.gmane.org] On Behalf Of Henry
Spencer
Sent: Monday, September 20, 2004 12:31 AM
To: Toronto Linux Users Group
Subject: [TLUG]: CD data recovery?

A low-tech :-) friend of mine asked me to inquire about this...

He's got a couple of CDs that are physically broken. (Shouldn't have
put them in checked baggage...) They're not mass-market items, and it
would be difficult to replace them without repeating some fairly
expensive travels. Anybody know of an outfit hereabouts that could
recover their contents, either as data files or as duplicate disks?

(These are music CDs, as it happens, but I've come close to needing this
once or twice for damaged CDROMs, and now he's got me curious too.)

Henry Spencer

henry-***@public.gmane.org

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[James Knott]

Post by Henry Spencer
A low-tech :-) friend of mine asked me to inquire about this...
He's got a couple of CDs that are physically broken. (Shouldn't have put
them in checked baggage...) They're not mass-market items, and it would
be difficult to replace them without repeating some fairly expensive
travels. Anybody know of an outfit hereabouts that could recover their
contents, either as data files or as duplicate disks?
(These are music CDs, as it happens, but I've come close to needing this
once or twice for damaged CDROMs, and now he's got me curious too.)

I've never heard of such as service, and you can be sure it would be
very expensive, if even possible. Anyone attempting such a recovery
would have to rejoin the pieces, to extremely close tolerances. Even
then they'd still have problems recovering the data.
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[lsorense-1wCw9BSqJbv44Nm34jS7GywD8/ (Lennart Sorensen)]

Post by James Knott

Post by Henry Spencer
A low-tech :-) friend of mine asked me to inquire about this...
He's got a couple of CDs that are physically broken. (Shouldn't have put
them in checked baggage...) They're not mass-market items, and it would
be difficult to replace them without repeating some fairly expensive
travels. Anybody know of an outfit hereabouts that could recover their
contents, either as data files or as duplicate disks?
(These are music CDs, as it happens, but I've come close to needing this
once or twice for damaged CDROMs, and now he's got me curious too.)

I've never heard of such as service, and you can be sure it would be
very expensive, if even possible. Anyone attempting such a recovery
would have to rejoin the pieces, to extremely close tolerances. Even
then they'd still have problems recovering the data.

I wonder if someone could scan the cd surface at very high resolution
(maybe with a laser beam) and then take the scans of each piece and lign
up the tracks that way and create a virtual cd image and recover the
data from that. Hmmm. Does sound expensive.

Lennart Sorensen
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[Peter L. Peres]

Post by lsorense-1wCw9BSqJbv44Nm34jS7GywD8/ (Lennart Sorensen)
I wonder if someone could scan the cd surface at very high resolution
(maybe with a laser beam) and then take the scans of each piece and lign
up the tracks that way and create a virtual cd image and recover the
data from that. Hmmm. Does sound expensive.

How much do you expect to pay for that service ? ;-)

Peter
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[lsorense-1wCw9BSqJbv44Nm34jS7GywD8/ (Lennart Sorensen)]

Post by Peter L. Peres

Post by lsorense-1wCw9BSqJbv44Nm34jS7GywD8/ (Lennart Sorensen)
I wonder if someone could scan the cd surface at very high resolution
(maybe with a laser beam) and then take the scans of each piece and lign
up the tracks that way and create a virtual cd image and recover the
data from that. Hmmm. Does sound expensive.

How much do you expect to pay for that service ? ;-)

Hmm, if there was demand enough for it they might be able to do that for
maybe $1000 or $5000 or something. No clue really. Better be an
important CD.

Lennart Sorensen
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[Henry Spencer]

Post by lsorense-1wCw9BSqJbv44Nm34jS7GywD8/ (Lennart Sorensen)
I wonder if someone could scan the cd surface at very high resolution
(maybe with a laser beam) and then take the scans of each piece and lign
up the tracks that way and create a virtual cd image and recover the
data from that. Hmmm. Does sound expensive.

Feasible in principle, I expect, but you'd need to work at exceedingly
high resolution, and it would get pricey...

(There are people already experimenting with scanning traditional
needle-and-groove LPs and recovering the sound, and apparently that can
be done, although at present the audio quality is too poor for it to be
a useful technique. But CDs are a whole different order of magnitude.)

Henry Spencer
henry-***@public.gmane.org

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[lsorense-1wCw9BSqJbv44Nm34jS7GywD8/ (Lennart Sorensen)]

Post by Henry Spencer

Post by lsorense-1wCw9BSqJbv44Nm34jS7GywD8/ (Lennart Sorensen)
I wonder if someone could scan the cd surface at very high resolution
(maybe with a laser beam) and then take the scans of each piece and lign
up the tracks that way and create a virtual cd image and recover the
data from that. Hmmm. Does sound expensive.

Feasible in principle, I expect, but you'd need to work at exceedingly
high resolution, and it would get pricey...
(There are people already experimenting with scanning traditional
needle-and-groove LPs and recovering the sound, and apparently that can
be done, although at present the audio quality is too poor for it to be
a useful technique. But CDs are a whole different order of magnitude.)

But CDs are also pits of known depths not analog variable depths the way
LPs are. It should be a simpler ting to determine what the correct
value is, although higher resolution. Not like laser discs which would
be a serious pain.

Lennart Sorensen
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[The Edge of the Ice]

Naturally gmail has decided to be helpful, and provided a relevant link:
http://www.acodisc.com

Good luck! (your friend will need it; that and it'd probably still be cheaper to
go and re-travel to get new discs rather than go through a data recovery house)

[lsorense-1wCw9BSqJbv44Nm34jS7GywD8/ (Lennart Sorensen)]

Post by The Edge of the Ice
http://www.acodisc.com
Good luck! (your friend will need it; that and it'd probably still be cheaper to
go and re-travel to get new discs rather than go through a data recovery house)

Or get someone to mail one.

Lennart Sorensen
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[James Knott]

Post by The Edge of the Ice
http://www.acodisc.com
Good luck! (your friend will need it; that and it'd probably still be cheaper to
go and re-travel to get new discs rather than go through a data recovery house)

I suspect that sort of service would fall into the "If you have to ask,
you can't afford it." catagory.

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[Henry Spencer]

Post by James Knott

Post by The Edge of the Ice
http://www.acodisc.com

I suspect that sort of service would fall into the "If you have to ask,
you can't afford it." catagory.

Yep, most likely. And I note that when they talk about physically damaged
disks, they mention scratches, not outright breaks.

Still, it's worth knowing that the outfit exists, just in case a real need
ever appears...

Henry Spencer
henry-***@public.gmane.org

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[James Knott]

Post by Henry Spencer

Post by James Knott

Post by The Edge of the Ice
http://www.acodisc.com

I suspect that sort of service would fall into the "If you have to ask,
you can't afford it." catagory.

Yep, most likely. And I note that when they talk about physically damaged
disks, they mention scratches, not outright breaks.
Still, it's worth knowing that the outfit exists, just in case a real need
ever appears...

Well, I do have an Enya CD, that's got a scratch in it. ;-)
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[Peter L. Peres]

Post by The Edge of the Ice
http://www.acodisc.com
Good luck! (your friend will need it; that and it'd probably still be cheaper to
go and re-travel to get new discs rather than go through a data recovery house)

I suspect that sort of service would fall into the "If you have to ask, you
can't afford it." catagory.

Actually the faq of acodisc says they do most cds for under $70 but it
does not mention anything about using superglue and tape to put the pieces
back together. What exactly did they do with that checked baggage ? Did
they deliver it by air mail (dropped out of baggage hold before landing) ?
I'm interested just in case.

Peter
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[Henry Spencer]

Post by Peter L. Peres
Actually the faq of acodisc says they do most cds for under $70 but it
does not mention anything about using superglue and tape to put the pieces
back together. What exactly did they do with that checked baggage ? Did
they deliver it by air mail (dropped out of baggage hold before landing) ?
I'm interested just in case.

He didn't supply details (indeed, may not have known details). It may be
that the bags got no more than the usual bashing and bouncing, but the CDs
shifted around enough to put them in a vulnerable position.

Henry Spencer
henry-***@public.gmane.org

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[Henry Spencer]

Post by James Knott
I've never heard of such as service, and you can be sure it would be
very expensive, if even possible. Anyone attempting such a recovery
would have to rejoin the pieces, to extremely close tolerances. Even
then they'd still have problems recovering the data.

However, given that the break won't be perfectly straight and will tend to
align itself, I wouldn't be surprised if a join to close tolerances wasn't
that hard, with the right equipment. You'd want to spin a patched-together
disk slowly, mind you.

Given how much error correction is built into the format, I suspect there
wouldn't be that much trouble doing an acceptable recovery, if the
alignment was close enough that the head servo could maintain track
following across the break.

(Still, I agree with the general conclusion that unless he's really nuts
about this particular music, recovery is probably too expensive...)

Henry Spencer
henry-***@public.gmane.org

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[John Macdonald]

Post by James Knott

Post by Henry Spencer
A low-tech :-) friend of mine asked me to inquire about this...
He's got a couple of CDs that are physically broken. (Shouldn't have put
them in checked baggage...) They're not mass-market items, and it would
be difficult to replace them without repeating some fairly expensive
travels. Anybody know of an outfit hereabouts that could recover their
contents, either as data files or as duplicate disks?
(These are music CDs, as it happens, but I've come close to needing this
once or twice for damaged CDROMs, and now he's got me curious too.)

I've never heard of such as service, and you can be sure it would be
very expensive, if even possible. Anyone attempting such a recovery
would have to rejoin the pieces, to extremely close tolerances. Even
then they'd still have problems recovering the data.

and the drive they used would have to be 1x or slower -
there's no way that a rejoined disk could handle the stress
of the current rotational speeds. (I recall hearing that
they were approaching the limit of the structural strength of
the glass disks, and would not be increasing much beyond the
current speeds.)

I suspect that to do the job properly would require a high
resolution scanner and special software to massage the image
to reconnect and clean up the area around the break/join.

[Henry Spencer]

Post by John Macdonald
there's no way that a rejoined disk could handle the stress
of the current rotational speeds. (I recall hearing that
they were approaching the limit of the structural strength of
the glass disks, and would not be increasing much beyond the
current speeds.)

The current disks (which are plastic, not glass) in fact cannot take being
spun at (say) 50x normal rotation rate, even though the label on the drive
does say "50X". There's some specsmanship there, based on the fact that
you can get the data rate up to 50x nominal at much lower rotational rate
if you're working near the outer edge of the disk. A 50X drive delivers
50x the data rate only in the most favorable part of the disk.

People have experimentally tried spinning CDs at the rate that would be
needed to deliver drive-specified rates near the inner edge. It's best to
have a blast shield around the disk when you do, because it will
disintegrate.

Henry Spencer
henry-***@public.gmane.org

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[James Knott]

Post by Henry Spencer

Post by John Macdonald
there's no way that a rejoined disk could handle the stress
of the current rotational speeds. (I recall hearing that
they were approaching the limit of the structural strength of
the glass disks, and would not be increasing much beyond the
current speeds.)

The current disks (which are plastic, not glass) in fact cannot take being
spun at (say) 50x normal rotation rate, even though the label on the drive
does say "50X". There's some specsmanship there, based on the fact that
you can get the data rate up to 50x nominal at much lower rotational rate
if you're working near the outer edge of the disk. A 50X drive delivers
50x the data rate only in the most favorable part of the disk.

And, due to CD layout, only full disks will ever use that 50X space,
though you could always pad the disk, so that the data is at the outside.

Incidentally, I believe you mean linear rate, not rotational. If
rotational, the outer tracks would be spinning faster or slower (RPMs)
than the inner tracks. That would definitely cause the disks to
fracture, no matter how fast they were spinning. ;-)
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[lsorense-1wCw9BSqJbv44Nm34jS7GywD8/ (Lennart Sorensen)]

Post by James Knott
And, due to CD layout, only full disks will ever use that 50X space,
though you could always pad the disk, so that the data is at the outside.

I believe dreamcast games took advantage of that and padded out their
games so the data was as far out on the disk as possible (they were also
modified CD format holding about 1GB, but same layout otherwise).

Post by James Knott
Incidentally, I believe you mean linear rate, not rotational. If
rotational, the outer tracks would be spinning faster or slower (RPMs)
than the inner tracks. That would definitely cause the disks to
fracture, no matter how fast they were spinning. ;-)

Well the read speed is a function of where on the disk the head is
pointing and how fast the disc is rotating. Since the data is stored at
a constant bits per distance of track, there is more data on one
revolution on the outside than the inside, hence at a constant rpm you
get higher read speeds at the outside than the inside. original CD
drives up to around 8x were constant linear speed, so they changed
rotation speed as they went along to keep a constant read speed, while
new drives use constant rotation speeds instead and have varying read
speeds as a result.

As far as I remember my 52x CD writer will only read pressed CDs at up
to 40 or 48x (probably 40x) to avoid damaging them, while cd-r it will
run at 52x. Supposedly they are more durable than pressed discs. The
drive is also supposed to have a reinforced front bezel, just in case :)
I don't want to know what the inside of the drive would look like if it
ever had a need to using that reinforcement.

Lennart Sorensen
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[James Knott]

Post by lsorense-1wCw9BSqJbv44Nm34jS7GywD8/ (Lennart Sorensen)

Post by James Knott
And, due to CD layout, only full disks will ever use that 50X space,
though you could always pad the disk, so that the data is at the outside.

I believe dreamcast games took advantage of that and padded out their
games so the data was as far out on the disk as possible (they were also
modified CD format holding about 1GB, but same layout otherwise).

Post by James Knott
Incidentally, I believe you mean linear rate, not rotational. If
rotational, the outer tracks would be spinning faster or slower (RPMs)
than the inner tracks. That would definitely cause the disks to
fracture, no matter how fast they were spinning. ;-)

Well the read speed is a function of where on the disk the head is
pointing and how fast the disc is rotating. Since the data is stored at
a constant bits per distance of track, there is more data on one
revolution on the outside than the inside, hence at a constant rpm you
get higher read speeds at the outside than the inside. original CD
drives up to around 8x were constant linear speed, so they changed
rotation speed as they went along to keep a constant read speed, while
new drives use constant rotation speeds instead and have varying read
speeds as a result.
As far as I remember my 52x CD writer will only read pressed CDs at up
to 40 or 48x (probably 40x) to avoid damaging them, while cd-r it will
run at 52x. Supposedly they are more durable than pressed discs. The
drive is also supposed to have a reinforced front bezel, just in case :)
I don't want to know what the inside of the drive would look like if it
ever had a need to using that reinforcement.

I'm aware of anglular velocity vs linear velocity. My comments were
simply a poor attempt at humour, regarding inner and outer tracks having
different angular or rotational velocity at the same time. ;-)

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[The Edge of the Ice]

On Tue, 21 Sep 2004 08:17:36 -0400, Lennart Sorensen

Post by lsorense-1wCw9BSqJbv44Nm34jS7GywD8/ (Lennart Sorensen)
As far as I remember my 52x CD writer will only read pressed CDs at up
to 40 or 48x (probably 40x) to avoid damaging them, while cd-r it will
run at 52x. Supposedly they are more durable than pressed discs. The
drive is also supposed to have a reinforced front bezel, just in case :)
I don't want to know what the inside of the drive would look like if it
ever had a need to using that reinforcement.

Unfortunately the original site appears to be down:
http://www.qedata.se/e_js_n-cdrom.htm

But there are others:
http://www.hifi-writer.com/he/misc/killercds.htm
http://www.powerlabs.org/cdexplode.htm

Now we're all waiting for those 500GB solid-state memories... ;)

[John Macdonald]

Post by The Edge of the Ice
Now we're all waiting for those 500GB solid-state memories... ;)
--
taa
/*eof*/

If you are will to wait a "little" while for the technical
details to get resolved, there will be much higher densities
than a mere 500GB.

IBM research has just demonstrated the ability to detect and
flip the spin on a single electron:

http://science.slashdot.org/article.pl?sid=04/09/21/135247&tid=126&tid=14

(But then you'll still have to wait a "little" longer for the
commercial details to get resolved to a consumer price level
you're willing to afford, of course.)

[James Knott]

Post by John Macdonald

Post by The Edge of the Ice
Now we're all waiting for those 500GB solid-state memories... ;)
--
taa
/*eof*/

If you are will to wait a "little" while for the technical
details to get resolved, there will be much higher densities
than a mere 500GB.
IBM research has just demonstrated the ability to detect and
http://science.slashdot.org/article.pl?sid=04/09/21/135247&tid=126&tid=14
(But then you'll still have to wait a "little" longer for the
commercial details to get resolved to a consumer price level
you're willing to afford, of course.)

So, you figure what, three weeks? Should be in Factory Direct, by the
end of the year. ;-)

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