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Optical Media FAQ

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Optical Media FAQ

Postby Bhairav on Thu Oct 21, 2004 1:17 am

Often one of the most overlooked facets of CD/DVD burning is the media in use. People often go and buy generic 0.1c media, and then complain of data corruption and loss! The truth of the matter is that media DOES matter, and can often make the difference between your data lasting for 5 years and 5 days!

By popular agreement, the best CD-R media was made by Kodak. But this was before they announced that they were leaving the market in March 2001. As a result, they are really difficult to obtain, and really expensive too.
But Japanese manufacturer, Taiyo Yuden,also make excellent CDRs.In fact,they were the company that invented recordable CD-Rs, and started it all out. Taiyo Yuden holds basic patents on CD-R, but so do Philips and Sony. Although TY conceptualized and did the actual work to physically invent CD-R, Philips and Sony may be credited as well in its final development


Patenting History of the CD-R disc

The error rates on these discs from just about any burner are very low.Other well regarded manufacturers include Ritek, Mitsui, Moser Baer India and Mitsubishi/Verbatim. But some Verbatim discs are made by CMC in Taiwan, and these are not very good, to put it mildly. The Verbatim discs manufactured by Mitsubishi in Japan are very good. The only way you can differentiate between them while looking at the packaging,is that the Mitsubishi Verbatim discs are manufactured in Japan, while the CMC Verbatim discs are manufactured in Taiwan.
Mitsui have followed Kodak, and are now on their way out of the optical media market.

Errors on CDR/RW discs are measured in terms of C1 and C2 errors. At the most basic (and this really oversimplifies and glosses over a lot), the C1 layer corrects the most common errors, the C2 layer corrects "bigger" errors that make it past the C1 layer, and the third layer that is included in mode 1 and mode 2 form 1 discs consists of extra data bytes used for EDC/ECC. It corrects errors that get past the C2 layer. In an audio disc the drive will attempt to mask errors that get past the C2 layer by guessing what the correct value should be. More reading material may be found here:


Errors on DVDR/RW discs, on the other hand, are defined as PI (Parity Inner) and PO (Parity Outer) errors. They are roughly analogous to C1/C2 errors on CD-R/RW discs,
C1/C2 and PI/PO errors can be measured using KProbe.
Read about KProbe, how to use it and download it here :
Do note that PI/PO testing will only work on Lite-On DVD writers, and C1/C2 testing on Lite-On CD/DVD writers.It is recommended to scan at 4X speed/8ECC during PI/PO testing and 40X during CD-R testing.

Explanation of PI/PO errors
Download the ECMA 267 Standard for DVD-ROM, the ECMA 337 Standard for DVD+R/RW and the ECMA 338 Standard for DVD-R/RW at http://www.ecma-international.org if you want to look at the standards for yourself. Here is some data from the ECMA standards (same for DVD-ROM, DVD-R/RW and DVD+R/RW):

Random errors:

A row of an ECC Block that has at least 1 byte in error constitutes a PI error. In any 8
consecutive ECC Blocks the total number of PI errors before correction shall not exceed 280.

Here we see what a PI error is defined as a row in an ECC block having 1 byte or more containing errors. And that the sum of PI errors in 8 ECC blocks after each other should not exceed 280 PI errors.

But what is a row and what is an ECC block? Again we refer to the ECMA standards. A row is 182 bytes long where the last 10 bytes contain PI (Parity Inner) information. An ECC block is 208 rows long where the last 16 rows contain the PO (Parity Outer) information. This gives us a maximum possible PI error amount of 208 errors per block and for 8 blocks after each other this sum is of course 8 times higher giving a maximum possible amount of 1664 PI-8 errors. In practical use a disc with 1664 PI-8 errors is unreadable.

But what are the PO errors that K-Probe reports? Actually the PO errors that K-Probe reports is the Parity Inner uncorrectable errors, meaning errors left after PI correction. Only the ECMA 337 standard describes the Parity Inner uncorrectable errors. So how is a Parity Inner uncorrectable error defined? Here is what the ECMA 337 states:

“If a row of an ECC Block as defined in 13.3 contains more than 5 erroneous bytes, the row is said to be “PI-uncorrectable”.”

In theory an ECC block may in the worst case have 208 PI uncorrectable errors since every ECC block is 208 rows long. But the ECMA 337 standard goes further and specifies the max amount of accepted PI uncorrectable errors allowed on a good disc:

“- In any ECC Block the number of PI-uncorrectable rows should not exceed 4.”

A guideline is to calculate the Parity Inner Uncorrectable errors to 8 ECC sum, which is max 32 (4 x 8) Parity Inner uncorrectable errors.

But what makes a disc unreadable? A PO uncorrectable error will make the disc unreadable, but K-Probe does not display the PO uncorrectable errors.

Easier explanation on how to read the test results.

Use this as a guideline for good discs:

PI(Parity Inner): No large areas on the disc should exceed 280 PI-8 errors,but do not worry too much about high single spikes that exceed 280.
PO(Parity Outer): No large areas on the disc should exceed 32 PO-8 (actually PI uncorrectable) errors,but do not worry too much about high single spikes that exceed 32.

And always, the lower your errors, the better.
Also, check out the media read curve in CDSpeed or KProbe: If there are any bumps or slowdowns, it's not a good sign.

Another error measurement software app: CDDoctor
Download/discussion :

Difference between DVD-R and DVD+R


Media Compatibility Threads

Media + Media Test Forum @ CDFreaks :

Sites To Visit.

The Media Sciences FAQ:

Jim Taylor's DVD recordable FAQ.

www.cdrfaq.org (Andy McFadden's excellent FAQ site.)




www.firmware-flash.com (best place for hacked RPC-1 DVD-ROM/R/RW firmware, and custom firmwares!)

http://www.cdpage.com (Excellent tutorials and articles.Highly recommended.)


Mike Richter's primer (parts of it a bit dated but still useful):
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