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Klendathu · Joined: 14 Feb 2005 Posts: 20

It is based on a 4.7GB DVD-R.
Dual layer does not increase density itself, it "merely" creates multiple layers with same density [double the surface so to speak]. I also supposed the 1.8GB to be single layer.

But it is well in the realms of the possible that games like lumnies are single layer umds, with the same data density as a dvd (wavelenght of laser as an indicator). effectively reducing maximum size to around 870MB

870MB are more than enough for such games as well as for movies encoded in mpeg-4 at full psp resolution. the 1.8 GB thing would then only be a promotion stunt. [remember Dreamcast "1.2GB" discs?] The resulting dual layer UMDs would then be even less accessible outside Sony HQ.
All in all delivering a cheap copy lock by easy means. something which sony seems to like if you remember the PS1 CDs the DVD integration in PS2 or the Blueray discs for PS3. They were typical optical discs which were easy to copy with no read protection and simple authentification tricks. but the required equipment was not widely available.

my guess is that they outfitted a minidisc drive with a standard DVD [single or double layer option scenario] or HD-DVD laser [always single layer scenario]. the only reason the numbers don't match perfectly is due to types of error correction.

on an interesting side note. play ridge racer and suspend to ram after the race starts but before the music starts. when you turn the psp back on, the game will continue instantly but the second the psp accesses the drive to start playing the music the psp will freeze until the disc is authenticated (?). after that the the race will go on but the music will only resume after the disc found the right track (halfway through the first tunnel if you play highway 776). this looks to me like classic IDE behaviour.
one more indication that sony just threw together already existant hardware instead of developing something truely new

mc · Joined: 12 Jan 2005 Posts: 212 Location: Link�ping

Klendathu · Joined: 14 Feb 2005 Posts: 20

Guest · Posted: Fri Feb 18, 2005 12:52 am Post subject:

Klendathu,

I am confused. Could you please explain the flavor of physics that you use to determine this ? Or is your frame of reference that of one layer being just above the event horizon of a black hole, whilst the other layer has fallen into the the aforementioned event horizon ?

Given 1 cm^2, how is the amount of information in a single layer the same density as that in a dual layer ?

Your sheet of paper analogy is wrong, and MC is correct. From a 2D point of view, your analogy of a stack of paper results in an increased density of information (or potential information) per cm^2 as a function of the number of sheets in the stack.

ooPo · Posted: Fri Feb 18, 2005 12:55 am Post subject:

There's no increase per cm^3.

Dual layer, not dual density.

You're both talking about different methods. Though only one would specifically apply to the dreamcast I guess...

Klendathu · Joined: 14 Feb 2005 Posts: 20

From human standpiont a dual layer dvd has twice the data desity of a single layer. because we humans see only the disc and the fact that the ammount of data has doubled:

X= Ammount of data
Y= Space
Z= density

human Point of View:
2X/Y=2Z

mc can only see the disc, the amount of data and thus calculates the density incorrectly.

My standpoint is from the technology point of view. I am the laser burning holes into the ground. my wavelength is fixed. It is also fixed how dense I can pack the data on any layer. I have however another option and that is to change my focusing point. if I (the laser) do this, the first layer disappears, and another one comes into my view. Humans might notice that the layers of a dvd are NOT two dimensional, they are above each other like floors of a building. I can wirte in each floor with the exact same density. Since these floors are so minute humans are given the impression that they are two dimensional, when in fact they are not. they are two two-dimensional discs stacked upon each ther. therefore the density remains the same YET THE SURFACE DOUBLES.

the laser can see the same thing an icehockeyplayer can. Both the surface of the ice AND the markings below.

2x/2Y=Z

Learn from the picture that a DVD9 simply has twice the surface. to write on. the laser does not magically improve on its ability to pack data denser together.

mc · Joined: 12 Jan 2005 Posts: 212 Location: Link�ping

[quote="ooPo"]There's no increase per cm^3.[/qoute]

Precisely. The density increases only because we're considering the surface area of the disc, not the volume. Nobody has measured the thickness of the UMD disc, or calculated the number of bits/cm�, so the facts that dual layer discs are thicker is largely irrelevant to the calculations.
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ooPo · Posted: Fri Feb 18, 2005 1:26 am Post subject:

'From human standpiont a dual layer dvd has twice the data desity of a single layer.'

Ahh, now we're getting into the realm of semantics and exploring definitions.

Definately correct, though. :)

mc · Joined: 12 Jan 2005 Posts: 212 Location: Link�ping

ooPo · Posted: Fri Feb 18, 2005 1:30 am Post subject:

With hopes of returning this back to the topic at hand:

http://darkwatcher.psxfanatics.com/console/optical_v2.htm

mc · Joined: 12 Jan 2005 Posts: 212 Location: Link�ping

Klendathu · Joined: 14 Feb 2005 Posts: 20

if it had a second layer the "surface that could be written to" would increase to 44cm�. since it would be two thin layers of 22 cm� above each other. according to sony 1.8 Gig is maximum size. but suddenly with a two layer 1.8 setup, the density would not be that different from a regular dvd. so all sony would have to do is to hook up a dvd lens to a MD drive and go.
this would greatly improve the chance of hustling some PC compatible device together.

mc · Joined: 12 Jan 2005 Posts: 212 Location: Link�ping

mc · Joined: 12 Jan 2005 Posts: 212 Location: Link�ping

Also, you can't make a multi-layer CD-ROM as the data layer is non-transparent.
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ooPo · Posted: Fri Feb 18, 2005 1:51 am Post subject:

I can't imagine any transparent layer being useful to lasers.

mc · Joined: 12 Jan 2005 Posts: 212 Location: Link�ping

No, but semi-transparent are.
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ooPo · Posted: Fri Feb 18, 2005 2:44 am Post subject:

So you can make a multi-layer cdrom, then?

mc · Joined: 12 Jan 2005 Posts: 212 Location: Link�ping

Nope. Because the data layer is non-transparent. I.e. it's fully opaque. Short memory?
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ooPo · Posted: Fri Feb 18, 2005 7:25 am Post subject:

Not at all. I just figured the layer would at least be reflective.

I guess that's why psx games are on totally black discs.

mc · Joined: 12 Jan 2005 Posts: 212 Location: Link�ping

Of course. All things which are not either entirely transparent (which, I trust, has now been clarified that the layer isn't :) or completely black (which not even the "black" PS CD:s are) are reflective to some extent. As for the "black" CDs, they have a film on them that filters out all wavelengths _except_ the one used by the laser. I've used CD-R:s with such film (from Traxdata) with my Dreamcast, so they work just like regular CD:s. The laser won't even notice that the film is there.
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mc · Joined: 12 Jan 2005 Posts: 212 Location: Link�ping

Just to cover all bases, since today seems to be "misunderstand everything-day", it is of course also possible for an object to be non-reflective if it is, say, 50% transparent and 50% black, i.e. 50% of the light is let though, 50% is absorbed, and 0% is reflected. Not that this has anything with CDs to do...
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ooPo · Posted: Fri Feb 18, 2005 2:15 pm Post subject:

So you can put only 50% of the data on that layer, while 50% of the laser burns into the label on the disc?

Victor · Joined: 26 Jan 2005 Posts: 15

like this?

pixel · Joined: 30 Jan 2004 Posts: 791

Ho god :) Do these burners still exist ? :P It was some funky yamaha, wasn't it ?
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Klendathu · Joined: 14 Feb 2005 Posts: 20

If you took a close look at the picture I posted earlier you would see that there is a difference between the layer which contains the information and the layer that reflects the beam.
one is still 100% reflective (but only for the laser wavelength)
the other is roughly semi reflective.
the layer which stores the data is in any case transparent.

if you took a cd which is "totally reflective" to your eyes and hold it into the sun you would also notice that some light passes through. the same goes for the black or blue discs. your eyes are tuned to frequencies ranging from 360nm to 680nm wavelength. so they will catch some light that can pass through the cd. within the boundaries of the Laser less light passes through. so a CD can still be "reflective" for the laser and look transparent to you or vice versa. but if you put less coating on top of it the sun too will start to damage the cd quicker.
jsut rung your own trials to see what I mean

and by the way, you can boil a cd without damaging it.

mc · Joined: 12 Jan 2005 Posts: 212 Location: Link�ping

Klendathu · Joined: 14 Feb 2005 Posts: 20

nope, the effect is quite dissatisfactory

F9zDark · Joined: 02 Apr 2005 Posts: 127

Well I took apart the UMD Sampler disc that came with PSP. First thing I noticed was that the metal plate in the center of the UMD disc, is rather permanent (perhaps I didn't try hard enough to remove it).

Secondly, the disc is too small to fit into a DVD rom drive. So I aborted the test (don't want to ruin my DVD rom).

Now the only viable reason I see for using UMD on the user level is music and movie data for the PSP. Memsticks are just too expensive (for me anyway) to make the PSP a viable game, movie and music venue. (even though I did put 5 of my favorite songs on the 32mb duo that comes with it).

But on the flip side UMDs are not commercially available for the end user and probably not a plausible medium to burn songs to. 1.8 gigs is a hell of alot of space to fill with songs, especially if it is not rewritable...

DBG · Joined: 28 Mar 2005 Posts: 12

Well this discussion has been all over the place, so I don't mind mucking it up a bit myself =). I have to believe a large reason for using UMD is marketing. Yes, it is also small and optical, but it will never be a consumer format, as Sony has already stated. I'm going to pop out a UMD disc (will probably trash Spiderman and the Sampler) and do my best to mount it on a spare drive and mess with the POT enough until I can read something or it smokes... I'll post a follow up if anything comes out of it ;).