Advise about 2nd hand DVD quickly.

[nick/slickrenderer]

Nothing to do with PS directly :-) Just value your advise.

Ok I made contact with a student in the same country as me. He has lot of training material that he wants to sell because he needs the money. I am buying some 3d training material from him. He says all the DVD's are in brand new condition.
He is going to be in my city today. I was thinking to meet him at the train station. I would open all the DVD's confirm they are original and not copies (I have some original ones I know exactly how they look...they are difficult to fake)

My question is-

If I confirm that they are original then do you think looking at the surface to see that there are no scratches will be enought to confirm that they will work?

The guy offered to come to my flat so that I can try each one of them.(actually preffers to exchange the money at my flat rather than at the train station)

I don't know what to do.I don't like the idea of a stranger coming into my flat.

I personally feel that according to him there is not a single scratch on any of the DVD's so if I can confirm this + that they are the genuine article then it would be good enough to confirm that they will work.

What do you advise? Urgent please as I have to write back to him.

I could meet him in starbucks maybe.What do you suggest?

[nick/slickrenderer]

:-)

[nick/slickrenderer]

All went ok. I met him is starbucks was a nice chap.

[Michael B. Field]

dvd's are a pain to copy and make labels for so if they aren't scratched they should be ok. If you have any concerns go to a place where you can play a few and make sure you can play them.

[Bill Lamp]

DVDs have the read surface on the bottom. CDs have it on the top where the label goes so you have to look for scratches differently. But by now you have probably tested them. I hope they all are OK.

Bill

[Bob Levine]

> CDs have it on the top where the label goes

Huh?

Bob

[dave milbut]

Huh²?

[Bob Levine]

Everyone is deep in thought. :)

Bob

[Bill Lamp]

The surface that is "burnt" is on the top with a protective coating/label over it. The lazer passes THROUGH the thick plastic stuff THEN writes. That is why you can buff out a scratch on the bottom of a CD and "repair" it. If you scratch the top coating, wave good by to the disk.

On a DVD, the write layer is at the bottom. The reverse location. The label is just that. It is NOT a protective layer. You can not buff out a scratch on a DVD, you just "break" it more when you try.

Look at a dedicated DVD case. The label is up and the bottom surface does not even touch the case. Even the cases are different because of how they work.

Bill

[YrbkMgr]

That's an odd way to say it Bill, although I see your point.

For clarification, all information is burned from the bottom, for both, CD's and DVD's. So I'm not sure what you mean about the reverse location thing.

[Bill Lamp]

HMmmm without a scratch pad. and there may be more layers in there.

W (OR READ) = the layer that is etched by the lazer
S = a support layer. The THICK one
P = protective layer - very thin
L = label layer - NOT on the dirt cheap ones.
Z = location of the lazer in the drive

Both of these are top to bottom.

A CD is built:
L
P
W
S - MOST of what you think of as a CD
Z

A single sided DVD is built:
L
S - MOST of what you think is the disk
W
P
Z

A double sided DVD is probably along the lines of:
P
W
S
W
P
Z

Flip it over and everything is still ready to read. The old top which the lazer didn't "see" is now on the bottom ready to be read and the old bottom is out of the way.

I have NO ideas as to how multiple burning depths work to be able to read several layers on each of the two sides. Ask & I won't answer.

It is the difference in where in the "stack" the write/read area is that makes double sided DVDs possible.

With the light beam having to pass THROUGH the support layer, a working double sided CD is impossible as the standard now exists. The W-layers would block each other from the lazer. And with DVDs on the market and all the current standard CD equipment out there, I don't really see it changing.

Perhaps, just perhaps this made it a bit more understandable. I hope so.

Bill

[YrbkMgr]

I see your point Bill. Good example.

[Bill Lamp]

Thank you.

[Michael B. Field]

There is a gold layer that the laser can read through on double layer pre recorded dvd's; The inner layer is alumunum. There is a protective plastic layer on the bottom of a dvd JUST LIKE CD's only thinner. If you scratch the top (lable) surface enough you will scratch into the dvd aluminum surface JUST LIKE CD's. A scratch on the bottom of a dvd can be repaired if it isn't too bad and it isn't radial. Many home theater dvd player have more error correction when they read a dvd than do dvd-rom players and dvd-burners; that is a dvd with a minor scratch in it may not play correctly on a pc because of a scratch, and it will play just fine on a home theater player. The problems with scratches on dvd's are just compounded by the amount of data on a dvd as compared to the amount of data on a cd. It is harder for a laser to see "around" the scratch on a dvd than a cd. The readable layer on cd's and dvd's is on top.

[Bill Lamp]

Michael,

I'm not saying your wrong, just that isn't how I was told. Perhaps I was misinformed.

From what you say, I shouldn't have to have to flip a movie DVD to shift from wide screen to letter box. The machine could just "read through" one layer to get to the next.

But I do have to do the disk flip, both on PC DVD units and a less than 1 year old stand alone reader unit for home theater. Both claim to read multiple recording depths. That seems to match the information I was given.

Bill

[Michael B. Field]

Bill,
Sorry, I got lost in that explaination. I know what I'm saying but you might not. These may help:

<http://www.geocities.com/Hollywood/Academy/6586/fac_d_02.html>

<http://www.disctronics.co.uk/technology/dvdintro/dvd_formats.htm>