How Data Stored In a CD

 
Abstract
You can fit on a S/VCD without over burning:
- 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 over burning:
- approx. 650 MB of data onto a 74min/650MB disc
- approx. 703 MB of data onto an 80min/700MB disc
 
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 (aluminum).
An a CD-R disc, the data is physically on an organic dye layer which simulates the metal layer on a real pressed CD.

 
How is the information structured
Now, on the CD, the information isn't just organized 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 organized 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.

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 unexcitable or ruin an achieve 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.


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 minSearch Amazon.com for sony bloggie touch
= 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
 
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).

DVD Writer Knowlede

16x Dvd+-rw Dl Dvd Writer Comparison Guide

Source:
CODE

http://www.extrememhz.com/dlcomp-p1.shtml

Since the introduction of double layer DVD writers, the interest has been quite overwhelming and is why we keep bringing you reviews of these highly popular drives. The anticipation has now turned into down right obsession and it has become a key component in any current or new system build, thanks to the declining prices and continued media hype. Manufacturers are quite aware of the fascination and is why they have each been releasing their own products which excel in at least one area of the testing methodology used in most reviews. This has led to some confusion as to which drive is best suited for the individuals needs. Today, we compare four 16x double layer drives and highlight both the strong and weak points in order to give you a better idea of which drive is best suited for you.


In this comparison guide, we will be looking at four of the top 16x drives to hit the market, the Pioneer DVR-108, NEC ND3500A, Lite-On SOHW-1633s and the new LG GSA-4160B. We will cover everything from design and features to performance and price. Let's begin with a quick look at each of these drives.


As far as the front bezel design goes, the LG-GSA4160B is by far the most attractive drive of the bunch. However, for those who are looking for a headphone jack, the Lite-On drive is the only DL writer offering a headphone jack, as well as volume control. The Pioneer and NEC drives, in my opinion, are the ugliest drives, with a very plain look that just wants to make you hide the drive period. Although we only obtained the 4160B in black, all these drives are offered with both white and black bezels. If you opt for the more expensive Pioneer "XL" model, it has the most impressive looks of any drive in the market. However, this will come at a very hefty price tag, considering they contain different firmware as well that offer a few extra features.

So, we have determined which is the sexiest-looking drive, but what about performance? I've done some extensive testing on each model to determine which is indeed the most impressive of the bunch. But before we show you performance results, let's briefly look at the features and what they have to offer.

Features



Each one of these drives has there disappointments when it comes to features. Let's compare each to see what they really offer.

NERO Burning Tools

DVD Writing



DVD+R DVD-R DVD+RW DVD-RW
LG GSA-4160B 16x 8x 4x 4x
Lite-On SOHW-1633s 16x 8x 4x 4x
NEC ND-3500A 16x 16x 4x 4x
Pioneer DVR-108 16x 16x 4x 4x



While all these drives are indeed 16x models, only two will write to both formats at this speed. The LG GSA-4160B and the Lite-On SOHW-1633s only support 8x DVD-R writing. So if you are one who only prefers this format, the NEC or Pioneer would be the best choice. All of these drives support writing to DVD re-writable media at 4x.



DVD+R9 Double Layer Writing



Write Speed
LG GSA-4160B 2.4x
Lite-On SOHW-1633s 2.4x
NEC ND-3500A 4x
Pioneer DVR-108 4x



The major disappointment with both the LG and the Lite-On 16x drives is the lack of 4x double layer writing support. Pioneer and NEC seem to be the only manufacturers to jump in and release second generation double layer drives supporting much faster 4x writing. In fact, the jump from 2.4x to 4x is quite substantial as we will show you a bit later in this comparison.



DVD-RAM Support



Supported Read Write
LG GSA-4160B YES 5x 5x
Lite-On SOHW-1633s NO NO NO
NEC ND-3500A NO NO NO
Pioneer DVR-108 YES 2x NO



Now this is where both the LG GSA-4120B and GSA-4160B shine above the rest. In fact, it is what has made these drives the most popular DVD writers on the market. Unlike the rest in the roundup, it is a triple format burner, offering full support for DVD-RAM media. The other drives do not support it, with the exception of the Pioneer DVR-108 which supports reading of DVD-RAM discs at 2x. I personally don't see the point in offering only read capabilities, but it's at least one extra feature added to distinguish it from the rest. Fast 5x support of the LG GSA-4160 will actually be tested a bit later in this article.



CDR Writing



CDR CDRW
LG GSA-4160B 40x 24x
Lite-On SOHW-1633s 48x 24x
NEC ND-3500A 48x 24x
Pioneer DVR-108 32x 24x



The fastest CDR writers of the bunch are the Lite-On SOHW-1633s and the NEC ND-3500A. With their support for 48x writing, they make a great all-in-one drive for many users. The only drive lacking in this lineup is the Pioneer DVR-108. Why they opted for only 32x writing is still quite puzzling and is actually why I have found that many are choosing the NEC over the Pioneer. The LG GSA-4160B should not be left out of consideration though. We will show you later that the difference in write times between 40x and 48x is not much to brag about.



Bitsetting Support



One feature I've found that is most important for many users is bitsetting support. Let's compare these drives and see what they offer.



DVD+R/RW Support DVD+R DL Support
LG GSA-4160B NO NO
Lite-On SOHW-1633s YES NO
NEC ND-3500A NO YES
Pioneer DVR-108 NO YES



The LG GSA-4160B does not offer bitsetting support out of the box. However, it is very likely that you will be able to obtain support through an excellent third-party tool called DVDInfo Pro. Right now, they only support the GSA-4120B, but I'm confident with the author that support for this drive will be likely. LG firmware is very hard to hack, however some select few have been able to do so. Using Lite-On's booktype utility, you can change the booktype of DVD+R/RW media, however, the firmware does not automatically change booktype of DVD+R DL discs to DVD-ROM like the NEC and Pioneer models do.



Additional Features



As far as other features go, all these drives have a 2MB buffer but offer some sort of buffer under-run protection, which all work exceptionally well. This is especially useful if you will be burning discs at 16x, which I personally don't recommend just yet. As our individual tests of these drives revealed, burning at this speed is quite unstable, with the exception of the Lite-On SOHW-1633s.