Is the cake bad ? (How much pressure can a DVD take before it loses it's data ?)

[Skybuck Flying]

Hello,

Sony for example sells dvd's which come in a "cake" package.

This means multiple dvd discs are stacked on top of each other without any
further protection except the cake around them.

The manual of a dvd recorder says:

"Don't stack discs".

No further explanation is giving.

I start to wonder: Why ?

I google and some simple explanatations pop up:

"Don't shuffle them like a deck of cards".

But I wonder, is this the true reason or is there more too it ?

My initial thought was:

It must be the gravity. Stacking DVD discs must be bad. The puts/dents which
are made in the DVD by the laser could bend back because of gravity and the
weight, resulting in data loss.

The special dvd jewel cases/enclosures could be ment to prevent that from
happening. Without the special dvd jewel cases the dvd's would be exposed to
too much pressure ?!?

So it's time to ask the following question:

How much pressure/weight can a DVD take before it loses it's data ?

Bye,
Skybuck.

 

[Tim]

Best not to stack disks at the beach on a windy day and then sit on
them..


D from BC
British Columbia
Canada

The problem happens after the blanks are burned. The chemical layer
tends to migrate out of the disc. The process is now known as "CD ROT".
Stacking the burned discs back in the cake pack will contribute to the
issue. The easiest way to to simply lay the cake box on it's side when
it has burned discs in it. Better protection can be provided with a
jewel case for each disc. If you use a case for each disc after they are
burned then the issue is somewhat halted. We won't know the actual life
expectancy of burned discs until the have aged considerably more, but
the general estimate is that it is going to be much less than the
earlier quoted 70 years.

- Tim -

 

[mpm]

The problem happens after the blanks are burned. The chemical layer
tends to migrate out of the disc. The process is now known as "CD ROT".
Stacking the burned discs back in the cake pack will contribute to the
issue. The easiest way to to simply lay the cake box on it's side when
it has burned discs in it. Better protection can be provided with a
jewel case for each disc. If you use a case for each disc after they are
burned then the issue is somewhat halted. We won't know the actual life
expectancy of burned discs until the have aged considerably more, but
the general estimate is that it is going to be much less than the
earlier quoted 70 years.

- Tim -- Hide quoted text -

- Show quoted text -

I thought the major contributor was scratches to the metalized side of
the disk (the side opposite of where the LED/laser diode scans.)

Perturbations here cause reflected light to scatter (and/or lose
intensity) eventually to the point where the read cannot take place.
The same happens to the scan side of the disk, but only as relates to
scattering, not total luminosity. Presumably, if you took the
reflective surface off altogether, you could not read the disk, even
though the scanned surface side could be in pristine condition.

Do you have a reference for the "chemical" argument you gave above?
I would be interested in reviewing that sometime. Thanks!

-mpm

 

[Skybuck Flying]

The hub of a CD or DVD is thicker than the recordable area. When you stack
the disks, only the hubs are touching.

Most interesting.

I held the cake up against a light bulb and there is indeed a small gap of
light/air between the dvd's recording area.

As you say only the hubs/centers are touching. I was wondering if the hubs
had a special function.

Sigh of relief

I guess the cake is good after all LOL.

I am not so worried about scratches... I rarely need to take them out of the
cake

I was more worried about the weight.

Bye,
Skybuck.

 

[Mike S.]

The hub of a CD or DVD is thicker than the recordable area. When you
stack the disks, only the hubs are touching.

Usually, but not always. I have a cake box of inkjet-printable Verbatim
DVD-R which is specifically marked as not having a raised hub. The discs
are flat.

 

[Gene E. Bloch]

Usually, but not always. I have a cake box of inkjet-printable Verbatim
DVD-R which is specifically marked as not having a raised hub. The discs
are flat.

Thanks for the warning

So much for relying on (what I thought was) a spec...

 

[Tim]

I thought the major contributor was scratches to the metalized side of
the disk (the side opposite of where the LED/laser diode scans.)

Perturbations here cause reflected light to scatter (and/or lose
intensity) eventually to the point where the read cannot take place.
The same happens to the scan side of the disk, but only as relates to
scattering, not total luminosity. Presumably, if you took the
reflective surface off altogether, you could not read the disk, even
though the scanned surface side could be in pristine condition.

Do you have a reference for the "chemical" argument you gave above?
I would be interested in reviewing that sometime. Thanks!

-mpm

I got that info when the first realization was made that burned cds go
bad. Do a search for "CD Rot" and you should find the info. It was on
the same site as the originator of the problem. This guy had thousands
of cds, and had about 25% go bad due to the problem. It was a major loss
for his pirated music collection.

- Tim -

 

[Mike S.]

Thanks for the warning

So much for relying on (what I thought was) a spec...

So did I. I never even dreamed they might be that way; ordered them online
based on brand and MID. They work, but I'm more careful with them in the
cake box.

 

[Gene E. Bloch]

So did I. I never even dreamed they might be that way; ordered them online
based on brand and MID. They work, but I'm more careful with them in the
cake box.

OTOH, if Guy Macon is right (for all values of printable disks), the
raised (lowered - I'm smiling too) hub on the bottom stands a good
chance of protecting the recording area, given reasonable handling.

 

[Mike S.]

Are those inkjet-printable DVD-Rs flat on both sides? Although IIRC
the spec calls for a raised hub on both sides, I can see a manufacturer
making a nonstandard product so that the printer has a flat surface
to work with, but I would have to assume that it still has a raised
(lowered? <smile>) hub on the bottom. I have designed a fair amount
of DVD and CD manufacturing equipment, and the basic idea of
grabbing a disc off of one spindle, processing it, and putting it
on another spindle is pretty much universal.

OK. I went back and looked. Yes, there is a teeny raised hub on the
bottom.