DVD Media Question

[t0rek]

OK, I know that DVD are supossed to be 4.7 Gb when they really are 4.38 Gb. I am aware of this, but I'm just wondering why they claim to be 4.7 Gb if they are not?

[JinXD]

Isn't it just the difference between using 1024kb per mb instead of 1000kb per mb?

edit: actually that doesn't make sence either, dunno?

[t0rek]

Are you sure?

[zman]

This is one of the oldest questions in computer history...

The answer lies in the floppy disket... Yes the floppy disket is one of the reasons people asked this question... So here's the answer... Any medium used by a computer needs to be formatted in order for that computer's OS to read that medium... So in the case of the DVD... The unformatted medium, which is not readable by any computer's OS is at full unused capacity of 4.7 GB a single Density DVD... Double Density is 9.2 GB... So when the DVD is formatted for the computer OS to read, that format information takes up space and thus you have what is left over to use... The remaining 4.38 GB... This is true on all medium used by a computer...

[t0rek]

OK zman, if what you said it's true, why 700 Mb CDs have real 700 Mb ?

[Stezo2k]

Isn't it just the difference between using 1024kb per mb instead of 1000kb per mb?

edit: actually that doesn't make sence either, dunno?

i'm pretty sure its that, they probably counted 1 MB as 1000kb NOT 1024kb, which is an actual megabyte

[t0rek]

i'm pretty sure its that, they probably counted 1 MB as 1000kb NOT 1024kb, which is an actual megabyte

Well, I'm aware that 1024kb is a megabyte, but why they didn't realize that?

[ScottJC]

Maybe because they are stupid? I wondered why this was the case as well, maybe there is an overhead... but its not totally uncommon just to dvd-r's, hard drives suffer this as well because they claim to be 80gb for instance and i end up only being able to see 75gb of it.. or something.

[-Shadow-]

That's strange, because can burn around 4500 GB on a DVD media without problems :plain:

[JinXD]

Quick check on google for anyone who doesn't understand the difference:

http://www.factmonster.com/ipka/A0881986.html
OR
http://www.riverland.net.au/text/look_first/gloss2.html

edit: Nah I was right first time:

1gb = 1024^3 = 1073741824b OR 1gb = 1000000000b

therefore

1073741824/1000000000 = 1.073741824 AND 4.7/4.38 = 1.073059361

[ScottJC]

Erm, Shadow, 4500mb IS 4.38gb ;)

[Stezo2k]

Well, I'm aware that 1024kb is a megabyte, but why they didn't realize that?

well its probably to make the dvd storage look bigger?

they do it with hard drives too, my 120 gig shows up at 111gig

[zAlbee]

yes, jinXD is right, zman is not.

hard drive manufacturers sell you 1,000,000,000 bytes instead of the real 1 gigabyte (1024^3). looks like DVD R does the same. just take 4,700,000,000 and divide by 1024 three times... you'll get 4.38 GB. floppy is the same 1,440,000 = 1.37 MB. CDs seem to be the exception... you get a nice and real 702 MB.

[Eagle]

Maybe because they are stupid? I wondered why this was the case as well, maybe there is an overhead... but its not totally uncommon just to dvd-r's, hard drives suffer this as well because they claim to be 80gb for instance and i end up only being able to see 75gb of it.. or something.


Thats different. 1st, Windows doesn't use all of a hard drive, it leaves part of it unpartitioned. Second a file system takes up disk space, small as it may be, it uses some. Third, cutting the silicone disks for a hard drive isn't an exact science, you cut it close to what you think it will be and then call it that, sometimes its more, sometimes its less. my 250GB hard drive has 258GB of unpartitioned space.

[ScottJC]

I meant in the terms of not having the exact space that they say, 4.7gb is not 4.38gb and 80gb is not 75gb... i'm just showing an example of similarity.

[t0rek]

So, Why CDs are an exception to the rule?

[Stezo2k]

So, Why CDs are an exception to the rule?

No idea... maybe the creators decided it was only fair to tell the truth?

Don't forget DVD was probably created by a different company

[MasterPhW]

That's strange, because can burn around 4500 GB on a DVD media without problems :plain:
What for a CD burner do you have? 4500 GB on one DVD? OMG! *lol*

A 700 MB CD means 700 MB, a 1GB CD/DVD would mean 1024 MB and a 4,7 GB DVD would mean 4812,8 MB...
Ups, now I'm confused!

[Stezo2k]

A 700 MB CD means 700 MB, a 1GB CD/DVD would mean 1024 MB and a 4,7 GB DVD would mean 4812,8 MB...
Ups, now I'm confused!

You are right about the 1st two, but 4.7Gig is not 4812MB

4700 / 1.024 = 4589.84

[Eagle]

You are right about the 1st two, but 4.7Gig is not 4812MB

4700 / 1.024 = 4589.84

No, he was right. There is 1024 MB in a gigabyte. If you have 4.7 gigabytes the calculation would be more like this

1024 * 4.7 = 4812.8MB

or if you want to break it down

1024 + 1024 + 1024 + 1024 + (0.7 * 1024)
4096 + 716.8
4812.8

I'm not sure what calculation you were doing.

[Jakob]

ok, not having read any of your posts I may well look like an ass.. but I'm going to lay it all out:
Mathematically speaking, a GigaByte is 1000 MegaBytes, a MegaByte is 1000 KiloBytes and a KiloByte is 1000 Bites.
In the world of computers, which natively use Base 2 math, things are somewhat different.... A GigaByte is 1024 or 2^10 MegaBytes, a Megabite is 1024 or 2^10 KiloBytes and a KyloByte is 1024 or 2^10 Bites.
Since Mathematically speaking, their claims to the space are true, they can legally slap 4.7GB on a 4.38GB disc.

now, your mathematically 4.7GB disc is computer terms 4 700 000 000 Bytes, 4589843 KiloBytes, 4482 MegaBytes, and finally, 4.38 GigaBytes.

[PsyMan]

He is evil, he is bastard, he sounds like an ass but he is RIGHT.

[smcd]

http://en.wikipedia.org/wiki/Kilobyte this explains it pretty well. Basically it came down to people who "knew about computers" understood that a kilobyte == 1024 bytes, and then when computers became more popular, people who knew numbers and not computers heard "kilo" and thought "oh, must be 1000"

[Eagle]

ok, not having read any of your posts I may well look like an ass.. but I'm going to lay it all out:
Mathematically speaking, a GigaByte is 1000 MegaBytes, a MegaByte is 1000 KiloBytes and a KiloByte is 1000 Bites.
In the world of computers, which natively use Base 2 math, things are somewhat different.... A GigaByte is 1024 or 2^10 MegaBytes, a Megabite is 1024 or 2^10 KiloBytes and a KyloByte is 1024 or 2^10 Bites.
Since Mathematically speaking, their claims to the space are true, they can legally slap 4.7GB on a 4.38GB disc.

now, your mathematically 4.7GB disc is computer terms 4 700 000 000 Bytes, 4589843 KiloBytes, 4482 MegaBytes, and finally, 4.38 GigaBytes.


So in a nutshell the answer to the original question...

Hard drives and DVDs use base 10 math for their capacity calculation and CDs and your computer uses base 2 math calculations. Which is why your computer sees CDs exactly as they are advertised but sees HD's and DVD's as less than what they are advertised.

[Jakob]

Eagle: yeah, I would imagine that the only reason that CDROM capacities are done in base 2(binary) math is becuase in the beginning, no one really expected personal cd burners, so the capacity wasn't a selling point, merely a technical sidenote.