CD-R Question

[Mitchum22]

This question may mark me as someone with hay still in his hair, but:

Why can we fit up to 6 hours(with rotten quality) on a standard DVD-R disc, but are limited to 74 or 80 minutes on standard CD-Rs? Why can't we manipulate the recording speed, bit rate, etc. in order to fit 90 or 100 or 150 minutes on a single CD-R?

Thanks!

[JohnnyMalaria]

The 74-minute limit on CDs refers to CD quality PCM audio (44.1kHz, 16-bit stereo).

You *can* encode 6 hours of MPEG2 video so that it will fit on a CD. It will look awful.

A CD can store 650MB of data (which equates to 74min of CD audio). This limit is defined by the size of the pits that are pressed (or burned for CD-R) to represent the digital data.

A single-layer DVD can store 4.7GB. The size of the pits used to represent the digital data are significantly smaller than for CD. And the laser needed to read (or write) has a smaller wavelength, too.

A dual-layer DVD can store 9.4GB.

The original question is a bit like asking "I can put a gallon of water in this gallon jug. Why can't I put a gallon in this pint jug?" It's because of the physical limitation of the container.

[JudgeGarth]

Okay, I'll go you one further: Why do we still even have CD's with such a limited capacity? I mean, the physical disks are the same size. I realize CD's have been around longer than DVD's. Is it because they don't want to obsolete all the old CD-only players that are still around? Does it actually cost a lot less to manufacture CD's as opposed to DVD's?

[aedipuss]

if you read the prior response carefully you will notice he already gave you the answer. a shorter wavelength laser is required to put more onto a disc. it's a physical limitation of all media/devices

[JohnnyMalaria]

all the old CD-only players that are still around?

There are plenty of NEW CD-only players around, too. Not everyone wants or needs to be able to play DVDs. e.g., I have no need for DVD compatibility for my in-car CD player.

I would also expect that the cost CD manufacturing equipment is less than for DVDs - older and more mature technology.

You must be quite young!

(Damn, did I really say that?!!!)

[JudgeGarth]

You must be quite young!

I wish! LOL!