Is 16x is as fast as DVD can get?

[wchou]

Is that the ceiling? like the sky's the limit?

 

[DaveSimmons]

Yes.

 

[Dr X]

Yup, it's the fastest DVD technology will ever burn....and computers will never have more than 512k of memory.

 

[Mark R]

It's the design limit of DVD. The discs aren't strong enough to withstand reliably the centrifugal forces at higher speeds.

CDs use a weaker plastic, and they reached a ceiling at a correspondingly lower speed (52x - although risk of disc breakage at that speed was quite high, so many '52x' drives actually shipped limited to 48x).

 

[wchou]

shouldn't dvd be at least 7 times faster then cd's being that its only 700mb so having 7 times the capacity should yield 48mb/sec so 32x dvd speed would still be possible if the rotation are 7200 rpm?

 

[n7]

DVDs burn at approx. 144x in CD terms IIRC.

Google for the technical explanation.

 

[wchou]

DVD is not CD so you cannot say it is 144x, this is like saying HD is 100x in terms of floppies but they are not related or compatible. 1x cd is 150kb/sec, 1x dvd is 1385kb/sec
48x CDR is as high as that technology will go, and since having 7 times the capacity, it should be 7 times faster theoritically speaking. So 7200kb/sec * 7 = 50,400kb/sec

 

[Pariah]

Originally posted by: wchou
shouldn't dvd be at least 7 times faster then cd's being that its only 700mb so having 7 times the capacity should yield 48mb/sec so 32x dvd speed would still be possible if the rotation are 7200 rpm?

What? You're combining all sorts of unrelated numbers into one incoherent statement.

A 1x DVD spins 3 times faster than a CDROM at 1x, which means a 16x DVD spins at the same rate as a 48x CDROM. Unsurprisingly, that spinrate (little under 10,000 RPM's) is the physical limit for both discs. Spin them any faster, and cheap discs begin shattering.

A 1x DVD reads data about 9 times faster than a 1x CDROM so a 16x DVDROM (21+MB/s) reads data 3 times faster than a 48x CDROM (7.2MB/sec).

 

[Tostada]

Everybody says that 16X max is pretty much the ceiling of DVD, but it should probably be 18X max. 52X max CD drives spin at 10,400 RPM. Discs can crack and explode if at higher speeds. Pioneer's zone 16X max DVD drives spin at 10,400 RPM at the beginning (but only 9,000 RPM at the end).

A CAV 18X max DVD drive would spin at a constant 10,260 RPM. Since there are already drives spinning faster than that, it shouldn't be a problem.

Originally posted by: wchou
shouldn't dvd be at least 7 times faster then cd's being that its only 700mb so having 7 times the capacity should yield 48mb/sec so 32x dvd speed would still be possible if the rotation are 7200 rpm?

That's really not true. An 80-min CD-R fits 737,280,000 bytes of data and a DVD-R fits 4,700,000,000 bytes. That's only 6.37 times higher capacity, and half of this capacity increase comes from fitting more tracks, not from fitting more data in each track. The track pitch of a CD is 1600nm. The track pitch of a DVD is 740nm. So you're getting twice the tracks on a DVD.

The outer edge of a CD fits 0.75KB per revolution. The outer edge of a DVD fits 2.43KB per revolution. A DVD is only transferring 3.24X more data in a single revolution. That is, if a CD and a DVD were both spinning at the same RPM, the DVD would only be 3.24X faster.

When you're comparing the X-factors, you also have to keep in mind that 1X CD starts at 500 RPM and goes to 200 RPM at the outside edge. 1X DVD starts at 1,600 RPM and goes to 570 RPM at the outside edge. So a lot of your increase in transfer speed comes from the fact that 1X DVD is spinning 3X as fast as 1X CD. If you multiply the DVD speed by 3, that gives you the comparable CD speed as far as RPM is concerned.

Originally posted by: wchou
DVD is not CD so you cannot say it is 144x

You can say it if you want. It's an accurate comparison of the transfer rate. It might not be the most useful comparison, but there's nothing wrong with it.

1X CD = 150 KB/sec
52X CD = 7,800 KB/sec
1X DVD = 1,385 KB/sec
16X DVD = 22,160 KB/sec

So 16X DVD is the same max transfer rate as 147.7X CD.

 

[fell8]

Who knows, maybe someone will bring back the multi-laser technology that let Kenwood CD-ROMs read at 72x 6 years ago.

 

[Tostada]

Originally posted by: fell8
Who knows, maybe someone will bring back the multi-laser technology that let Kenwood CD-ROMs read at 72x 6 years ago.

TrueX drives didn't actually use multiple lasers. It was still easy to make those drives relatively cheaply because they used a single laser with a diffraction grating. The laser is split into seven beams which shine onto the disc then are picked up by a simple sensor.

A burner couldn't use that technology because the beams couldn't be turned on and off independently. Actually using multiple lasers would be more expensive and much more difficult.

There were supposed to be 25X TrueX DVD-ROMs several years ago, but that never happened. It looks like it's been abandoned.