Data capacity of CDs

[vitualis]

The capacity of a CD disc

Abstract
You can fit on a S/VCD without overburning:
- approx. 735 MB of MPEG data onto a 74min/650MB disc
- approx. 795 MB of MPEG data onto an 80min/700MB disc

You can fit on a CD-ROM without overburning:
- approx. 650 MB of data onto a 74min/650MB disc
- approx. 703 MB of data onto an 80min/700MB disc

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Introduction
Let us ignore for now the terms of megabyte for CD capacity and try to understand how the data is stored on a CD.

As well all know, the data is stored digitally as binary data. This means, however the actual information is actually kept on the disc, this information is in the form of "1"s and "0"s. Physically, the information on a CD is as pits on a thin sheet of metal (aluminium).

An a CD-R disc, the data is physically on an organic dye layer which simulates the metal layer on a real pressed CD.

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How is the information structured
Now, on the CD, the information isn't just organised from beginning to end willy-nilly. Otherwise, it would be really hard to find a useful piece of information on the CD.

Rather, the information is organised in sectors. Consider a sector as like a page in a book. Just like you are able to quickly find something in a book if you know the page number, you can quickly find something on a CD if you know the sector number.

Now, remember that the CD was original made to hold audio data. It was decided, that the CD would would 75 sectors per second of audio. Although I cannot guess where this number comes from, it is quite appropriate for the audio CD. It means that you can "seek" an audio CD accurately to 1/75th of a second -- which is more than enough for consumer purposes.

Now, with this in mind, we can work out the total data capacity of user data for 1 sector.

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The total data capacity of user data of 1 sector on a CD
CD audio uses uncompressed PCM stereo audio, 16-bit resolution sampled at 44.1 kHz.

Thus 1 second of audio contains:
16 bits/channel * 2 channels * 44100 samples/second * 1 second
= 1411200 bits
= 176400 bytes

Since there are 75 sectors per second
1 sector
= 176400 bytes / 75
= 2352 bytes

One sector on a CD contains 2352 bytes max.

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The concept of different MODES and FORMS of burning
Now, audio CD was well and good, but the medium would become much more useful if you could store other data on the disc as well. This became to be know as CD-ROM of course.

Now, the audio-CD uses the ENTIRE sector for audio data.

However, for CD-ROMs this caused a problem. Simply, CDs and the CD reading mechanisms were not 100% faultless. That is, errors (indeed frequent errors) could be made during the reading. For audio CDs, this does not matter as much as you could simply interpolate from the adjacent audio samples. This will obviously NOT DO for data CDs. A single bit error could lead to a program being unexecutable or ruin an achive file.

Thus, for CD-ROMs, part of each sector is devoted to error correction codes and error detection codes. The CD-R FAQ has the details, but in effect, only 2048 bytes out of a total of 2352 bytes in each sector is available for user data on a data CD.

This burning mode is either MODE1 or MODE2 Form1.

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MODE2 Form2 sectors of VCDs and SVCDs
Now, for VCDs and SVCDs, the video tracks do not necessarily require the robust error correction as normal data on a CD-ROM. However, there is still some overhead per sector that is used for something other than video data (e.g., sync headers).

S/VCDs video tracks are burnt in what is called MODE2 Form2 sectors. In this mode, only 2324 bytes out of a total of 2352 bytes in each sector is available for user data.

This is MUCH MORE than for CD-ROMs, but still less per sector than audio CD.

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The disc capacities of CD-ROMs, audio-CDs and VCDs
Now, obviously what ultimately determines the capacity of a disc is the total number of sectors it contains. This is similar to the total number of pages in a blank exercise book (if you recall the book analogy).

The secondary determinant is the burning mode of the disc.

For audio CDs, it is as if you could fill each page from top to bottom with audio data as the entire sector is used for audio data.

For CD-ROMs, it is as if you need to first rule a margin and then leave the bottom part of each page for footnotes (headers + ECC + EDC). The amount of text you can actually write per page is then less due to these other constraints.

For S/VCDs, we still need to rule a margin on the page, but we don't have to worry about the footnotes (headers). We can fit MORE text than a CD-ROM, but less than an audio-CD.

Now remember, 1 second on a CD = 75 sectors.

Thus:
- 74 min CD = 333,000 sectors
- 80 min CD = 360,000 sectors


Data capacity in Mb for an audio-CD
74 min
= 333,000 sectors * 2352 bytes / sector
= 783216000 bytes
= 746.9 Mb

80 min
= 360,000 sectors * 2352 bytes / sector
= 846720000 bytes
= 807.5 Mb


Data capacity in Mb for a CD-ROM
74 min
= 333,000 sectors * 2048 bytes / sector
= 681984000 bytes
= 650.4 Mb

80 min
= 360,000 sectors * 2048 bytes / sector
= 737280000 bytes
= 703.1 Mb


Data capacity in Mb for a S/VCD
74 min
= 333,000 sectors * 2324 bytes / sector
= 773892000 bytes
= 738.0 Mb

80 min
= 360,000 sectors * 2324 bytes / sector
= 836640000 bytes
= 797.9 Mb

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Conclusions
As you can see, the often quoted capacities of 650MB and 700MB refer to CD-ROM capacities.

Due to the fact that S/VCDs use a different burning mode where MORE of each sector is available as user data, the relatively capacities are HIGHER.

Now, since S/VCDs are not composed of PURELY video tracks and have some unavoidable overheads, the actually total capacity left for video tracks is a few Mb less for each disc (about 735 Mb for 74min discs and 795 Mb for 80min discs). This is where the often quoted capacities of 740MB and 800MB come from. They are quite accurate.

All these capacities are available BEFORE overburning. Overburning is where you burn MORE sectors than the disc is rated for. If you overburn, you can typically achieve about 1-2 minutes of additional capacity (depending on your drive and media).

I hope this finally puts this topic to rest!

Regards.

[Askani]

Great Info, keep up all the great work.

[Anonymoususer]

This is a very interesting topic I have sucessfully burned 823MB's yes MBS not Bytes MegaBytes by overburning and making an SVCD that is almost 3 Minutes more...I don't know how but it seems to have burned it and the CD worked..what is the highest amount burned soo far...lookin for some other people who have burned more than this..

[ryanreko]

great topic, good base information
i look forward to future topics

[Marty2002]

I'm no expert, well in fact, you might consider me a newbie, but I think you made a mistake somewhere in your calculation. I went over everything and it seems correct, but I'm guessing the number of sectors per disc might be wrong. Through experience, I'm about 99% sure a 80 min video cd holds more then 797.9 MBytes without overburn. they hold closer to 805MB. My cd burner does not support overburn, so there's no chance of me overburning my discs. From another site, I read cd's in mode2 form2 hold 172KBytes per second.

172 KB * 60 seconds * 80 minutes = 825600 KB per CD
825600KB / 1024KB per MB = 806.25 MB per video cd

this number seems closer to the actual capacity of video cd's

[jolo]

This is phenominal information. I knew it went farther than 700MB, but wasn't sure how far.

Then to explain it as well.

An A+++ for effort and a A+++ for quality of information.

Now if we can get vendors like Nero to understand this, we'd be in good shape.

Jon

[BJ_M]

I'm no expert, well in fact, you might consider me a newbie, but I think you made a mistake somewhere in your calculation. I went over everything and it seems correct, but I'm guessing the number of sectors per disc might be wrong. Through experience, I'm about 99% sure a 80 min video cd holds more then 797.9 MBytes without overburn. they hold closer to 805MB. My cd burner does not support overburn, so there's no chance of me overburning my discs. From another site, I read cd's in mode2 form2 hold 172KBytes per second.

172 KB * 60 seconds * 80 minutes = 825600 KB per CD
825600KB / 1024KB per MB = 806.25 MB per video cd

this number seems closer to the actual capacity of video cd's

you are right but didnt read carefully -- depends on if you use 2352 bytes or 2324 bytes / sector which he explained ..

80 min
= 360,000 sectors * 2352 bytes / sector
= 846720000 bytes
= 807.5 Mb

[BJ_M]

......................
Now if we can get vendors like Nero to understand this, we'd be in good shape.

Jon

nero understands this perfectly ... what do you mean ?

Well written, but won't it reduce the amount of postings on the forums by half? People won't have what to ask!

Speaking of which, Philips added some description of 99min CDs to the standard, but because there might not be competability with all players you can't use CD logos on them (anyone here cares about that?)

http://www.licensing.philips.com/senl/news/documents496.html

Maybe add this CD's capacity to the list too? Should be some 980-982MB for (S)VCDs...

[Cornucopia]

Something to mention:

While the rated capacity of CD's is

- 74 min CD = 333,000 sectors
- 80 min CD = 360,000 sectors

YMMV, because it's kinda like the MSRP(manufacturer's stated retail price).
You should usually get at least as much as that (unless you've got some junk discs), but it's quite possible to get discs that have somewhat more, depending on the formulation and batch. E.G 74 min CD with 340,000 sectors or 80 min CD w/ 368,500 sectors.

How to tell? It should be readable in the ATIP. Most burner apps have some function or utility that does this. Usually, it's in the Recorder/Disc Info area. Or you could use a standalone app. Check Google and you'll find some. Nero's CD speed includes a good one.

So this variance may be the reason behind some claims about getting 800 MB onto a VCD...

Scott

[vitualis]

Thanks for the info! To quote directly from Philips:

September 30, 2002
High Capacity Recordable Disc system, Version 0.9, dated Sept 2002

This document describes High Capacity Recordable discs with a maximum single session time of 98 minutes, 29 seconds, 74 frames on 12 cm discs. For 8cm discs the playing time will be roughly 30 minutes.

The recorded High Capacity Recordable is not fully compliant with the Red Book, but will be playable on the majority of the installed base CD players.
To avoid any misunderstanding about the compatibility of the High Capacity Recordable Discs: The use of a CD logo is not allowed on this disc.

Wow, Philips is disallowing the use of the CD logo on these discs!

In any case, 98 min, 29 sec and 74 frames = 443249 sectors

Thus, in terms of max. user data capacity (without overburning):
Audio CD (or 2352 bytes per sector): -- size of WAV files in Mb
= 443249 sectors * 2352 bytes/sector
= 1042521648 bytes
= 994.2 Mb


S/VCD (or 2324 bytes per sector): -- size of MPEG in Mb
= 443249 sectors * 2324 bytes/sector
= 1030110676 bytes
= 982.4 Mb

Remember, there is usually up to 10 seconds of unavoidable overhead on a S/VCD so the max. size of MPEG you can put on without overburning is closer to 980 Mb.


CD-ROM (or 2048 bytes per sector): -- size of data in Mb
= 443249 sectors * 2048 bytes/sector
= 907773952 bytes
= 865.7 Mb

Regards.

[kim_tanch]

Hey, Thank to vitualis for posting such a good detailed information.

After rad about it, I have tried to burn data into VCD, which is the format can hold more capacity.
I used the standard VCD format in Nero to do this. I drag the folders into the window of VCD format in Nero. In order to burn it, I drag a small mpeg movie into it, which is about 3 kB. The size of VCD is displayed as 762 MB (76:01:24). The VCD is created successfully using a Samsung 80 Min CDR.
Then, I displayed the VCD's properties with window explorer,
It is look like this:-

Size: 673 MB (705,869,691 bytes), 708,968,448 bytes used

Why the size displayed are different in the window and Nero?
How can i fully utilize the capacity of the disc in the VCD format?
Is the process I described about is right?

Thank, I am a newbie. I am appreciate all the help and comment.

Windows will show you the size as if it was written in 2048 byte sectors. To see the size, go to Nero, then go to the "Recorder" menu, and then to "Medium-Info". The first clip you burnt will appear at the second track, the second clip as third track and so on....

[130T|_|L15/\/\]

I've seen using VCDEasy that a 80 min disc can have 807 megabytes on the disc, I have never done that before. Sometimes with SVCDs I get quite close to the 800 megabyte barrier, sometimes 802 or even 803 megabytes. The MPEG2 file that I used was around 790+ megabytes. My CD reader/writer drive does support over burning so that could explain being able to place 807 megabytes on a CD-RW HS 80minute disc.

I think it's too bad there isn't a program that tells you how much you can overburn... I did do a test where I over burn an Audio CD with the intension of making it too big, and later played it on a system to see how far will it play. If I want the burning to finnish wihout errors (Everything is written, and then leadout) I can have about 82.5min. If I over burn till it just can't go on I get about 83min.

[sunmanking]

Hello,

Thank you for the impressive guide you've written. It has solved
many of the doubts I had concerning data capacity on cd-r.
Actually, I think it has solved EVERY doubt I had! Thank you
for taking the time to write it and explain it in detail.

I appreciate,

Luis

PS. BTW, You've dealt with every cd-r disc capacity but
90 min cd-r... Is there any special reason to avoid it?

Last: has anyone tried out 90-in and 100-min cd-r as
vcd or svcd on the dvd-player? Was the result successful?
This is VERY important as we could hold more data, and so
more minutes, per cd BIG thanks.

[Craig Tucker]

Well written, but won't it reduce the amount of postings on the forums by half? People won't have what to ask!

I think thats wishfull thinking. Some people still ask, how do I convert my AVI to MPEG. You will always get people who cant be arsed to read the information that is right under their nose, just because it is easier to ask someone else.

[Craig Tucker]

Well written, but won't it reduce the amount of postings on the forums by half? People won't have what to ask!

I think thats wishfull thinking. Some people still ask, how do I convert my AVI to MPEG. You will always get people who cant be arsed to read the information that is right under their nose, just because it is easier to ask someone else.

[EddyH]

Wow, cool stuff, thanks KJ... this explains why the timings are never quite "right" with my VCDs there's an 18 byte loss on each frame! That kind of makes things a bit more right with a 795mb file, a 5mb and 4mb, and a few pictures, needing to be written to about 814mb (81mins 15sec) by nero instead of the neat 807mb (79m59s) I'd planned!
(and then the CD writer having problems where it normally works OK with 81m-xx overburn discs?)

For the length of the disc being recorded in the ATIP, you'll never see one that describes itself as more than 79m 59s 74f, as that's the maximum recordable value in that field or something. 80 mins was as high as it was ever designed to go, regardless of all the old-time CD players' manuals stating what happens to the display if you insert a disc "longer than 100 minutes"...

I like the neatness of how the stated length of the 99 minutes CDs - 98 and a half, minus a frame - makes them to be almost exactly 100 minutes including the lead out. Anyone want to try overburning one of those babies to 100m 01s and seeing what happens?
(they could be just the thing for some TV series AVIs I have - whoever the nonce was who made them, made them to be 280mb long... what kind of useless length is that? too big for a single 8cm (unless you use a 30m & mode2form2), probably won't even fill a 63min CDR with two (560mb), but is far too big for any overburnt disc with three (840mb!!) >_<)

[EddyH]

Sunmanking, to be cheeky, I would say

Startmenu -> Programs -> Accessories -> Calculator

80 minutes info, divided by 80, multiplied by 90, should get a good answer
(hehe)

(though oddly I've seen enough burners advertised by their 86 and 88 minutes CDR compatibility... not 90... weird)

[sunmanking]

Hi EddiH,

Yes, I knew about that possibility I just was wondering
if there was a reason not to mention it.

Anyway, thank you for the reply and thanks for the guide!

Greetings,

Luis

[sunmanking]

Hello again,

I have tried CDR Media Code Identifier v1.63 and checked the
capacity of a blank 80-min Intenso cd-r.

The info the program provides me is the following:

ATIP: 97m 32s 19f
Disc Manufacturer: Prodisc Technology Inc.
Reflective layer: Dye (Short strategy; e.g. Phthalocyanine)
Media type: CD-Recordable
Recording Speeds: min. unknown - max. unknown
nominal Capacity: 702.83MB (79m 59s 73f / LBA: 359848)

A blank 80-min Imation gives:

ATIP: 97m 26s 66f
Disc Manufacturer: CMC Magnetics Corp.
Reflective layer: Dye (Short strategy; e.g. Phthalocyanine)
Media type: CD-Recordable
Recording Speeds: min. unknown - max. unknown
nominal Capacity: 702.82MB (79m 59s 71f / LBA: 359846)

Can anyone please tell me what is the difference between
the ATIP value and the nominal capacity value? Of course,
nominal capacity is what "there is" in the cd to be burnt,
but ATIP capacity... Also, why different ATIP values?
Could that mean every single cd-r could be overburnt to
97m 32s 19f in the case of Intenso cd-r???

Thank you!

Luis

[MpegEncoder]

What about the space used by the Lead-in and Lead-out areas?

[eusebio]

Thank you very much for a well written and clear description. I am writing a bitrate calculator for the pinnacle bungee and this info will be very helpful.

By the way, summarizing what others have hinted, for added accuracy it would be necessary to consider:

* The size of the ISO section (without user files, just a minimal SVCD ISO track)
* The size of session lead-in/lead-outs
* That nominal capacity is rarely 360,000 sectors for a 80 min CD and burning programs warn about overburning for any size beyond this nominal capacity

[vitualis]

@ EddyH:

Wow, cool stuff, thanks KJ...

As for burning over 100minutes, Tom's Hardware Guide had an article about 90 and 99min discs. From memory, on those players that could play such discs (i.e., CD-DA players), the display stopped working properly.

As for information in the ATIP, it is not always reliable -- especially if produced by third party / "cheapo" OEMs.

@ eusebio:

The absolute minimum size of the ISO track (i.e., track 1) of a S/VCD is 6 seconds long. Any additional files will increase the size. Each still image on a S/VCD as a segment item takes up 2 seconds of capacity (150 sectors).

Since S/VCDs can only be burnt as one session only you can ignore the size of the "disc" lead-in area as it is not included in the stated capacity of a disc. This is similarly so with the disc lead-out area. Since the lead-out area is always about 1 and a 1/2 minutes long, you can usually safely overburn up to 1 and 1/2 minutes of user data (i.e., into the lead-out area) as long as you burn the disc in DAO mode. Even if the disc burn fails during the burning of the "lead-out" area, the disc itself is usually okay as the lead-in/TOC has already been written and all the data has been written.

For S/VCDs (at least those authored by VCDImager), there is a 2 second lead-in and 2 second lead-out overhead for each MPEG track.

@ sunmanking:

PS. BTW, You've dealt with every cd-r disc capacity but
90 min cd-r... Is there any special reason to avoid it?

Last: has anyone tried out 90-in and 100-min cd-r as
vcd or svcd on the dvd-player

Um, I didn't deal with 99min CDs either (until mpegobssession linked to the Philips site...)

In any case, if you take 90min CDs to be actually 90min in capacity, then you can do the same calculations as detailed above.

As for trying out these discs, I have tried out 90min discs. They worked well. I have not tried 99min discs. Reports would suggest that these discs are not quite as compatible as 90min discs.

Regards.

[EddyH]

thanks KJ

oops, i meant virtualis, of course


The ATIP / Nominal values thing, oops again, I screwed that up. Asolute Time In Pre-groove these days is generally used as a unique identifier of the company that made the CDR (mostly are in the 97m+ range, from back when 80 mins was a rare thing and thought to be really pushing the envelope). Indeed this is what any programs that identify the type, composition and origin of CDRs read.

The nominal value is what you're after, in terms of recordable non-overburn length! (yay for the boffins that have "74" minute discs with Nom values of 75m+, non-OB dudes... sadly, though ATIP does indeed go all the way up to 100, Nom is the one which maxes out at 79'59"74).

[wchang99]

I think it's too bad there isn't a program that tells you how much you can overburn...

Nero has a little app called Cdspeed, it comes with the Nero Burning Rom package and I'm pretty sure you can dnld it for free (I did, but not too recently) -- it will test a cd for overburn capacity, along with a bunch of other tests...

[Anonymoususer]

they need to just come out with regular CD;s that are big as DVD's which are about 4.7GIGS..life would be very easy...

Thanks wchang99, didn't know of that option there!

DivXerouS,
Sony did start doing that, with the DD-CD that would have capacity of 1.3GB... But nothing except DD-CD drives can read it and it came out now, when DVD+-R drives are getting more popular, so the entier thing was dropped...

[Tiribulus]

Positively splendid information!! This explains why simply making big .mpg files and burning them as data does not provide the capacity of actually using a video mode to do the burn.
Tiribulus