Posted by Voinin on 05/03/06 00:31

Henry Nettles wrote:
> On Mon, 01 May 2006 15:50:47 -0700, Voinin <vboing@boing.biz> wrote:
>
>> Silicon Sam wrote:
>>> Yeah, I have some TY made Sony's rated at 8X that will burn at 12X.
>>> Speed is no concern to me, so all mine get burnt at 4X. Just ordered
>>> 300 of the TY 4X's from Meritline. They support 8X burn as well. Free
>>> Shipping, they work out to around 24 cents each. TY is supposed to be
>>> the benchmark in blank DVD's
>>>
>>> I have a PC and a Mac, so when my PC is duping a DVD, I flip the
>>> switch and use the Mac in the meantime.
>> My question wasn't so much if you could burn them slower or anything
>> like that. What I want to know is what criteria do the manufactures use
>> to determine max burn speed of a disc. I generally burn at 8X on all
>> discs that support faster speeds.
>
> By "manufacturer", do you mean disc manufacturer or drive
> manufacturer? The company that manufactures the discs rates them for
> a maximum speed, primarily based on the dye. The drive manufacturer
> uses an eprom on the drive to store the "firmware". Embedded in the
> firmware is a list of "MEDIA ID"s. For instance, the Taiyo Yuden 8x
> DVD-R media referenced above has a MEDIA ID of "TYG002". The drive
> reads this information from the blank disc, and then matches the MEDIA
> ID against a table stored in the firmware. Based on this table, the
> drive knows that it has two write strategies for this particular blank
> disc, a 4x write strategy and a 8x write strategy. These "write
> strategies" are also stored in the firmware, which is why it is
> important to be sure your DVD recorder has the latest firmware.

I know the gross mechanics of what goes on with burning a disc; i.e. the
laser causes the dye substrate to change color, making it appear similar
to a commercial disc to the player.

What I'd like to know is the finer aspects of this. For example, why
does burning slower work when burning faster fails? It seems that the
laser isn't as accurate at fast speeds than it is at slow speeds, but in
what way is it not as accurate? I sort of see a little elf in my drive
marking the disc with a little pencil when the proper area of the disc
is overhead. It would seem that the little elf would know that if the
disc is spinning faster he has to mark at a faster speed so that the
mark does not vary in size on the disc. (Marking a faster disc at the
same speed as a slower disc would end up creating a larger mark.) He
also needs to be able to write to the correct location on the disc and
so has to be pretty good at his timing when the disc is spinning faster.

So I see there are three factors here:

1) The responsiveness of the dye to laser light. Because the disc is
moving faster at higher speeds and the specific location that the laser
is writing to is moving faster, the laser doesn't have as much time to
expose the dye and so the dye has to be more sensitive to the wavelength
the laser is using. This begs the question: are faster discs more prone
to decay by ambient light than discs rated for slower burn speeds?

2) The drive itself must have better accuracy when determining which
part of the disc is above the laser.

3) The drive must also have better accuracy and timing when turning the
laser on and off.

So there are a number aspects here and I'm not sure I understand why
burning a disc rated for a specific speed doesn't work at that speed as
well as it does at lower speeds. It seems there's a bit of fudging
things up a bit.

--
I'm just driving this way to piss you off.

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