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# CD and DVD speed

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### #1 biferibiferi

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Posted 12 March 2015 - 11:20 PM

If I have a Blank CD and it says the speed on it is 23  or say 18 am I right this just meens how long the Laser will stay on one spot one the Disc before it move to another spot as it Burns Data?

### #2 Platypus

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Posted 13 March 2015 - 02:14 AM

The speed figure is how many times faster than an original Audio CD the disc is spinning. Inevitably, if the rate of rotation doubles, the time for which any point on the disc is over the laser is halved.

So at 32x speed, the laser has only half the time to burn each pit as it has at 16x speed.

Also, for double the rotation speed, the laser mechanism will travel at twice the speed in its linear traverse that traces the spiral data track.

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### #3 Rocky Bennett

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Posted 13 March 2015 - 09:28 AM

Another way of looking at it would be to say that if a CD was burned at 32x speed, then you could burn 32 minutes of data in one minute.

### #4 biferibiferi

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Posted 13 March 2015 - 03:40 PM

So if I use a DVD that says 16x speed I can Burn 16 MIN. of Data in One Min. am I right?

### #5 YeahBleeping

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Posted 13 March 2015 - 04:37 PM

16x speed refers to the ' recomended rotation ' or burn speed if you burn a disc at 16x this translates to roughly 24.93 mb/second

So at 16x burn speed in one second you can transfer almost 25mb/second but it takes around 6 minutes to write this data. Just because the drive can transfer that amount of data in one second doesn't mean that the laser can burn it ' in ' one second.  Generally the faster the rotation speed the more times the laser will see the same spot.

I thought I should add that in my example the merry go round represents the dvd Me and you represent the laser and the rocks represent the amount of data to send.

Think of a Red piece of wood on a merry go round. We each have a pile of 40 rocks to throw at the red piece of wood.

If me and you each have our own merry go round and:

My merry go round is spinning at 18x and yours is spinning at 1x

Lets say that equates to 1 round per minute

In one minute I see that piece of wood 18 times and you only see it once.  So I can throw 18 rocks at that piece of wood when you can only throw one in one minutes time.

It will take you 40 minutes to empty your pile of rocks and it will only take me about 2 and a half minutes.

Edited by YeahBleeping, 13 March 2015 - 04:48 PM.

### #6 Platypus

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Posted 13 March 2015 - 04:42 PM

If the burn actually achieves the theoretical 16x, then yes, the amount of data that would take 16 min to play as standard DVD video would be written in 1 minute. (The time to write the data stream onto the track - disregarding any other operations like updating the file system or finalizing the disc.)

It's not that accurate to relate speed to time with DVD data, as video data is adaptive, and 16 minutes of video can require varying quantities of data.

In essence, for any writable disc, one rated as 16x speed can theoretically write data in 1/16th the time a disc with only 1x speed rating would take.

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### #7 Platypus

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Posted 13 March 2015 - 04:55 PM

So at 16x burn speed in one second you can transfer almost 25mb/second but it takes around 6 minutes to write this data. Just because the drive can transfer that amount of data in one second doesn't mean that the laser can burn it ' in ' one second.

Is this what you actually meant to say? If it took 6 minutes to write 25Mbyte, it would take 36 hours to write a dual layer DVD.

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### #8 YeahBleeping

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Posted 13 March 2015 - 06:42 PM

Thanks Platypus for the insight on my mistake.  Lets just say it takes about 40 mins to write 8gb. data which is about 3.4 gb per second.  The math changes as the laser moves closer to the cylinder center.  I'll leave this thread with a link to a good Q/A on DVD.

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