EAC Drive Options: Difference between revisions

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EAC is the most powerful and advanced ripper available, it delivers the highest quality rips possible and unsurprisingly is the most popular ripping software at Hydrogenaudio. There's one catch, configuring it correctly is a newbie's nightmare. This guide will take you through all necessary steps of the configuration, so you will be able to enjoy high quality compressed audio no matter how advanced you are.
{{EAC guides}}
The EAC '''Drive Options dialog''' (shortcut: F10) offers several options for configuring how [[EAC]] reads and writes audio data from the currently selected drive.


<small>''Used EAC version: V0.99 prebeta 5''</small>


==Software Needed==
==Extraction Method==


To begin with, [http://exactaudiocopy.org/eac6.html download EAC] and unzip it to a folder of your choice.
===Secure Mode===


'''Note:''' ''This tutorial assumes you are installing EAC for the first time, i.e. that the default settings are set to start with. If this is not the case, you can reset them by doing the following:''
You will need to detect & apply drive features when using secure mode.  Even if you chose to use the configuration wizard, it's a good idea to repeat the test a couple of times in order to be sure that the results are consistent (see [http://www.exactaudiocopy.de/en/index.php/overview/basic-technology/automatic-feature-detection-technology/ link]). Beware that these features are unique to every drive.
* ''Press <Windows Key> + <R> (or click 'Start | Run'), type '''regedit''', and hit <Enter>.''
* ''Go to the key ''HKEY_CURRENT_USER\Software\AWSoftware\EAC'', and delete it by pressing '''Del'''.''


====Drive has 'Accurate Stream' feature====


==EAC Configuration Wizard==
: Back around the turn of the century when digital audio extraction (DAE) was relatively new, some drives couldn't provide audio data from precise locations. Each time it was told to read a block of audio, a drive might produce data that was shifted slightly ahead or slightly behind. When an adjacent block of data from a subsequent read is shifted, it will either begin with samples repeated from the previous block, or samples between the blocks will be omitted.  In DAE, this phenomenon is often called jitter or synchronization error.  To compensate for this problem, EAC is able to overlap every read in order to detect and correct any misalignment.


* Upon running EAC for the first time, a setup wizard will appear. Close it by clicking ''Cancel'', and '''close and restart''' EAC.
: Essentially all drives produced today have a feature called 'Accurate Stream' which significantly reduces (if not completely eliminates) the chance that audio data will be shifted between successive reads. When informed that a drive has this feature, EAC will only periodically overlap its reads to check for synchronization problems.
**'''Important:''' ''We have to do this to circumvent a bug in EAC which makes the program configure your reading devices (CD-ROM/DVD/CD-RW drives) incorrectly when it is first run.''
* After restarting, re-run the config wizard by clicking EAC -> Configuration Wizard. Keep a clean Audio CD handy, you'll need it in a minute to test and configure your drives.
* Click '''Next'''; EAC will now list all CD drives it found in your system (all of them should be checked). Click '''Next''' again.
* You will now be asked what read mode to use for the drive. Be sure to enable '''I prefer to have accurate results''':
[[Image:Wizard_accurateresults.png|none|frame|I prefer to have accurate results]]
* Click '''Next''' again. On the next page, click '''I don't trust these values, detect the features for my drive'''.
[[Image:Wizard_donttrust.png|none|frame|I dont trust these values]]
* Now, insert an Audio CD (Original, factory-pressed CD only. No CD-Rs, CD-RWs or bootlegs.) into your drive (if you have more than one, you will see in the window which one to use), and click '''Next''' twice. EAC will now perform some tests in order to determine your drive's capabilities, and display the results within a few minutes.
[[Image:Wizard_results.png|none|frame|Detection results]]
*If this is the case, click '''Next''' again. If you have more than one drive, the same procedure must now be repated for the other drives; once all drives have been tested, a summary like this will be displayed:
[[Image:Wizard_driveranking.png|none|frame|Drive ranking]]
*Don't rely on this. This is purely a feature-based ranking (mainly dependant on the '''Audio Caching''' feature which is an obstacle for secure audio extraction) - it provides no assessment of the drives' actual ripping quality (in this example, EAC is completely wrong - the NEC drive is totally unreliable for audio extraction, while the Lite-On is excellent). You will have to test this for yourself later.
*Now, click '''Next''' again. EAC will now ask you whether or not you would like to configure the LAME encoder - uncheck the appropriate option, and proceed to the next page:
[[Image:Wizard_lame.png|none|frame|Uncheck 'Install and configure the external LAME.EXE compressor']]
*You will now be asked for your e-mail address in order to access the freedb online music database. You needn't enter your real one, something like this will do:
[[Image:Wizard_freedb.png|none|frame|Enter e-mail address]]
*Click '''Next''', and select ''I am an expert, let me use the full potential of EAC'' on the next page:
[[Image:Wizard_expert.png|none|frame|Expert mode]]
*Don't worry about it if you're not an expert ;-) - this tutorial explains all important options. Also, when run in Beginner Mode, EAC resets some settings that are important to us.
*Click '''Finish''' now to close the wizard.


==EAC Options==
:* If the "Detect Read Features..." function reports "Accurate Stream : Yes", it is safe to check the "Drive has 'Accurate Stream' feature" box. This will result in a significant increase in ripping speed.


Check out the EAC options in the EAC menu. While there isn't necessarily much you should change, it is important that you set error recovery quality to "high". Notice that the below Coaster Factory tutorials are for EAC 0.9 Prebeta9, so don't take everything as a fact. Once you have configured EAC options as per the Coaster Factory tutorials, continue reading this article and configure the drive and encoder as instructed below.
====Drive caches audio data====


[http://users.pandora.be/satcp/eac02p.htm Coaster Factory (CONFIGURING EAC OPTIONS)]
: In order for secure mode to work properly, every read request made by EAC must cause the drive to seek data from the CD.  If your drive caches audio, subsequent requests for the same data may result in the drive only fetching this data from its buffer, rather than from the physical disc. To prevent this from happening, EAC has a routine to ensure previously requested data gets flushed from drive's cache. This is done by having the drive read extra data from the disc—more data than the cache can store.


==CD-ROM Drive Options==
:* If the "Detect Read Features..." function reports "Caching : Yes", it is important that you enable the cache flushing routine by checking the "Drive caches audio data" box.


For perfect rips, you should setup your CD-ROM drive correctly (secure mode options, offset correction options, gap detection options). Go to the drive options in EAC menu and follow these instructions:
:* If the "Detect Read Features..." function reports "Caching : No", it is not necessary to enable the flushing routine.  Checking the "Drive caches audio data" box with drives that are reported by EAC as not caching will ''not'' improve EAC's accuracy. It won't improve EAC's ability to detect errors nor EAC's ability to correct them. What it ''will'' do however, is reduce your ripping speed and shorten the life of your drive.


Drive Setup (done once):
: '''Tip #1''': If you're concerned that your drive caches audio data even though EAC is saying otherwise, try ripping a scratched disc (one known to produce errors easily).  Make sure you uncheck the "Drive caches audio data" setting AND uncheck the "Drive is capable of retrieving C2 error information" setting.  Make sure you also set the error recovery quality to "Low" (this setting can be found under the Extraction tab in the [[EAC Options]] dialog). If EAC is capable of displaying a ''read'' error then cache flushing isn't necessary.  Ignore any sync errors that may be displayed; they are irrelevant to this test.


Select: ''Secure mode with the following drive features (recommended)''
: '''Tip #2''': Tip #1 is all you need to know, but if you're still paranoid that your drive caches audio, feel free to try {{brokenlink|http://www.feurio.com/English/Download/download_install.shtml|Feurio's}} audio caching test (Ctrl+Alt+P\Test device\Cache test) or spath's [https://club.myce.com/t/cache-explorer/167099 cache explorer] (also forked as [https://github.com/xavery/cachex cachex]). Tests should be performed with an audio CD in the drive. If either determine that your drive doesn't cache or caches less than 64 KB of data, then cache flushing isn't necessary (ignore the reported buffer size when using cache explorer).  The reason for the 64 KB barrier is that EAC will never request less than this amount while ripping [http://web.archive.org/web/20140626091839/http://www.digital-inn.de/threads/cache-detection-in-eac.32972 link]).


You will need to detect & apply drive features when using secure mode but only if you chose not to use the configuration wizard otherwise you can skip drive setup. Beware that these features are unique to every CD-ROM drive
: '''Note''': If "Drive has 'Accurate Stream' feature" is deselected, then "Drive caches audio data" is automatically checked, regardless of whether the drive actually caches audio data.


===Drive Features===
====Drive is capable of retrieving C2 error information====


; Accurate Stream/Drive has ‘Accurate Stream’ feature : If EAC reports "Accurate Stream: Yes" your drive doesn't jitter this will decrease the probability of errors & cause a speed increase, enable this option by ticking the "Accurate Stream" box.
: This setting was designed to speed up the ripping process by trusting the drive's ability to reliably report uncorrectable errors.<ref>"Uncorrectable" doesn't mean the data is bad, necessarily. In fact, it's normal for at least a portion of data marked uncorrectable to actually be correct; it just wasn't made correct by the C2 system.</ref> If this setting is enabled, EAC will not re-read and try to get consistent data from sectors which the drive reports as being error-free. Unfortunately, not all drives adhere to the same standard as to how this should be done. As a result, errors can go undetected.


; Caching/Drive caches audio
: EAC has two tests for this feature.  The "Detect Read Features..." function only tests if the drive says it can provide C2 error information. The "Examine C2 Feature..." function tests whether the drive can actually report an uncorrectable error. Neither test can be used to determine whether ''all'' uncorrectable errors are reported, so these tests don't tell you whether the setting can be used reliably.
: If EAC reports "Caching: Yes" your drive caches audio data, every sector read will be read from cache and is identical, this will increase the probability of errors & cause a speed decrease. EAC needs to clear the cache by overreading it, enable this by ticking the "drive caches audio" box.


: Tip: EAC may misinform about audio caching as an alternative you can use [http://www.feurio.com/English/Download/download_install.shtml Feurio's] audio caching test found in Feurio.exe\Ctrl+Alt+P\Test device\Cache test.
:* You may be able to determine if your drive's C2 reporting is reliable in EAC by using [http://www.exactaudiocopy.de/en/index.php/other-projects/dae-quality/ DAE Quality]. This involves creating a special CD and testing it.


: Tip: Some drives disable audio caching at low speeds, if your drive is set to DMA transfer mode try changing it to PIO only transfer mode then re-test for caching.
:* Unless you know that you can use this setting reliably, ''disable'' it.  If you choose to enable it, make sure you also rely on AccurateRip or a test CRC to compare with the read CRC if AccurateRip doesn't have data for your disc.


: Tip: If you are not sure whether your drive caches audio data or not (or if you don't want to use Feurio's audio caching test), as a rule of thumb, enable this option. This might result in lower ripping speeds, but the results will be far more accurate.
===Paranoid Mode===


; C2 Error Info/Drive is capable of retrieving C2 error information
This is an old mode that has been superseded by secure mode.  It is highly unlikely that this mode will provide any benefit over secure mode.  
: With C2 enabled EAC's error detection becomes dependent on the drives C2 accuracy which varies from drive to drive & increases the probability of errors, this feature also results in a speed increase because EAC doesn't read the data twice anymore, If your drive supports this feature & you decide to use it enable this by ticking C2 Error Info box.


: Tip: To determine your drives C2 accuracy you could attempt creating a [http://www.exactaudiocopy.org/eac13.html DAE Quality] test CD. This takes a long time though. If you are not completely sure your drive supports C2 correctly you should disable this feature in EAC.
===Fast Mode===


: Tip: If you are not sure whether your drive is capable of handling C2 error information, as a rule of thumb, disable this option. Once again, this might result in lower ripping speeds, but the results will be far more accurate.
This is another old mode for drives that cannot provide a synchronized stream when ripping in burst mode.  Since synchronization error is no longer a problem with modern drives, it is highly unlikely that this mode will provide any benefit over burst mode.


So an ideal drive would support accurate stream (tick) & wouldn't cache audio (no tick). However, there is no need to spend a fortune on buying a new drive. EAC works well with almost any decent drive available in the market to give you near-perfect results; provided EAC is configured properly as per instructions given above.
===Burst Mode===


==Additional Reading==
Burst mode performs extraction without any error checking.  It is handy for discs that do not require re-reading in order to be ripped accurately, especially with drives that cache audio data.  It is also handy for discs that trigger re-reading in secure mode but cannot be ripped accurately.  When used in conjunction with AccurateRip, or in conjunction with a test CRC to compare with the read CRC in the event that AccurateRip doesn't have data for your disc, burst mode is completely secure.
* [http://users.pandora.be/satcp/eac03p.htm The Coaster Factory EAC Drive Configuration]
 
* [http://users.pandora.be/satcp/eacoffsets01.htm#- The Coaster Factory Offset Table]
==Drive==
* [http://www.offsetbase.eac-audio.de/offset-en.php Eac-Audio.de Offset Table]
'''Drive read command'''
* [http://www.hydrogenaudio.org/forums/index.php?showtopic=32151 List of DAE Drive Features, EAC & CD Paranoia] by westgroveg
: ''(Default: Autodetect read command, '''Recommended: use the Autodetect read command now button''')''
This drop-down list allows users to configure which read command to use with the drive to extract audio.
 
 
'''Autodetect read command now'''
 
This button will set the proper read command in the Drive read command drop-down list.
 
 
'''"Big Endian" byte order (Motorola)'''
: ''(Default: disabled)''
This option reverses the byte order of the audio data coming from the drive.  If the ripped audio is loud static, change this setting.
 
 
'''Swap channels'''
: ''(Default: disabled)''
This setting reverses the stereo channels of the ripped audio. If you find that your drive reverses channels, it is probably due to a two-byte offset which cannot be corrected properly with this option.  Try upgrading your drive's firmware or replace it with a different model.
 
 
'''Spin up drive before extraction'''
: ''(Default: disabled)''
This option may or may not improve performance.  Enable it if your drive doesn't otherwise operate smoothly or cannot rip the beginning of a track correctly.
 
==Offset / Speed==
'''Use read sample offset correction'''
 
'''Detect read sample offset correction...'''
 
'''Use combined read/write sample offset correction'''
 
'''Overread into Lead-In and Lead-Out'''
 
'''Speed selection'''
 
'''Allow speed reduction during extraction'''
 
'''CD-Text Read capable drive'''
 
==Gap Detection==
The goal with both of these settings is to help EAC get ''reasonable'' gap values in a reasonable amount of scanning time. There is no way to know if the values are 100% correct.
 
'''Gap/Index retrieval method'''
:EAC offers three methods: A, B, and C; the difference between them is unknown. Method A is a good initial setting, as it is usually fast and provides good results, but on some discs and some drives, B or C might be better.
 
'''Detection accuracy'''
:This affects how many times the gap info is read. Inaccurate is one read, so it will be fastest. Accurate and Secure are multiple reads, which will be slower but may perform better on some CDs, especially if scratched or defective.
 
Background info:
 
Indexes are track subdivisions. All tracks have index 01 for the main content. Some also have a "gap" (index 00) for a between-song pause (silence or very quiet hiss), or for a non-silent interlude, count-in, or applause. On rare occasion, tracks will have higher-numbered indexes as well.
 
The start of each track's index 01 is listed in the CD's table of contents, so it is known as soon as the disc is inserted. The other indexes are stored in the disc's subcode, which can be difficult to read correctly. CDs also have slight variances in how and where this info is stored. EAC's Gap Detection settings help cope with these issues.
 
What are reasonable results?
* Gaps are all different lengths, and in a range of about 1 to 5 seconds each.
* Gaps are all exactly 2 seconds each (for a CD-R burned in TAO mode).
 
What are suspicious results?
* Gaps are all the same length, and not exactly 2 seconds each.
* Gaps are all very short—e.g., less than 1 second each.
* Gaps are all very long—e.g., over 1 minute, or equal to the track length.
* Gaps extend well beyond the end of a pause/interlude in the music.
* Gaps get progressively longer.
 
These are general guidelines; there will be occasional exceptions.
 
==Writer==
'''Writes samples offset'''
 
'''Create Offset Test CD'''
 
'''After Burning Finished'''
:'''reset drive by ejecting and loading CD-R'''
 
:'''only eject CD-R'''
 
:'''do not eject CD-R'''
 
'''Drive is able to write UPS/ISRC'''
 
'''Drive is able to write CD-Text'''
 
'''Detect Write Features...'''
 
==Notes and references==
<references/>
 
==External links==
* [http://www.hydrogenaudio.org/forums/index.php?showtopic=32151 List of DAE Drive Features, EAC & CD Paranoia] by WestgroveG
* [http://www.daefeatures.co.uk/ DAE Drive features database] By WestgroveG and Evereux
 
[[Category:EAC Guides|Drive & EAC]]

Latest revision as of 11:21, 12 June 2023

The EAC Drive Options dialog (shortcut: F10) offers several options for configuring how EAC reads and writes audio data from the currently selected drive.

Used EAC version: V0.99 prebeta 5

Extraction Method

Secure Mode

You will need to detect & apply drive features when using secure mode. Even if you chose to use the configuration wizard, it's a good idea to repeat the test a couple of times in order to be sure that the results are consistent (see link). Beware that these features are unique to every drive.

Drive has 'Accurate Stream' feature

Back around the turn of the century when digital audio extraction (DAE) was relatively new, some drives couldn't provide audio data from precise locations. Each time it was told to read a block of audio, a drive might produce data that was shifted slightly ahead or slightly behind. When an adjacent block of data from a subsequent read is shifted, it will either begin with samples repeated from the previous block, or samples between the blocks will be omitted. In DAE, this phenomenon is often called jitter or synchronization error. To compensate for this problem, EAC is able to overlap every read in order to detect and correct any misalignment.
Essentially all drives produced today have a feature called 'Accurate Stream' which significantly reduces (if not completely eliminates) the chance that audio data will be shifted between successive reads. When informed that a drive has this feature, EAC will only periodically overlap its reads to check for synchronization problems.
  • If the "Detect Read Features..." function reports "Accurate Stream : Yes", it is safe to check the "Drive has 'Accurate Stream' feature" box. This will result in a significant increase in ripping speed.

Drive caches audio data

In order for secure mode to work properly, every read request made by EAC must cause the drive to seek data from the CD. If your drive caches audio, subsequent requests for the same data may result in the drive only fetching this data from its buffer, rather than from the physical disc. To prevent this from happening, EAC has a routine to ensure previously requested data gets flushed from drive's cache. This is done by having the drive read extra data from the disc—more data than the cache can store.
  • If the "Detect Read Features..." function reports "Caching : Yes", it is important that you enable the cache flushing routine by checking the "Drive caches audio data" box.
  • If the "Detect Read Features..." function reports "Caching : No", it is not necessary to enable the flushing routine. Checking the "Drive caches audio data" box with drives that are reported by EAC as not caching will not improve EAC's accuracy. It won't improve EAC's ability to detect errors nor EAC's ability to correct them. What it will do however, is reduce your ripping speed and shorten the life of your drive.
Tip #1: If you're concerned that your drive caches audio data even though EAC is saying otherwise, try ripping a scratched disc (one known to produce errors easily). Make sure you uncheck the "Drive caches audio data" setting AND uncheck the "Drive is capable of retrieving C2 error information" setting. Make sure you also set the error recovery quality to "Low" (this setting can be found under the Extraction tab in the EAC Options dialog). If EAC is capable of displaying a read error then cache flushing isn't necessary. Ignore any sync errors that may be displayed; they are irrelevant to this test.
Tip #2: Tip #1 is all you need to know, but if you're still paranoid that your drive caches audio, feel free to try Feurio'swbm audio caching test (Ctrl+Alt+P\Test device\Cache test) or spath's cache explorer (also forked as cachex). Tests should be performed with an audio CD in the drive. If either determine that your drive doesn't cache or caches less than 64 KB of data, then cache flushing isn't necessary (ignore the reported buffer size when using cache explorer). The reason for the 64 KB barrier is that EAC will never request less than this amount while ripping link).
Note: If "Drive has 'Accurate Stream' feature" is deselected, then "Drive caches audio data" is automatically checked, regardless of whether the drive actually caches audio data.

Drive is capable of retrieving C2 error information

This setting was designed to speed up the ripping process by trusting the drive's ability to reliably report uncorrectable errors.[1] If this setting is enabled, EAC will not re-read and try to get consistent data from sectors which the drive reports as being error-free. Unfortunately, not all drives adhere to the same standard as to how this should be done. As a result, errors can go undetected.
EAC has two tests for this feature. The "Detect Read Features..." function only tests if the drive says it can provide C2 error information. The "Examine C2 Feature..." function tests whether the drive can actually report an uncorrectable error. Neither test can be used to determine whether all uncorrectable errors are reported, so these tests don't tell you whether the setting can be used reliably.
  • You may be able to determine if your drive's C2 reporting is reliable in EAC by using DAE Quality. This involves creating a special CD and testing it.
  • Unless you know that you can use this setting reliably, disable it. If you choose to enable it, make sure you also rely on AccurateRip or a test CRC to compare with the read CRC if AccurateRip doesn't have data for your disc.

Paranoid Mode

This is an old mode that has been superseded by secure mode. It is highly unlikely that this mode will provide any benefit over secure mode.

Fast Mode

This is another old mode for drives that cannot provide a synchronized stream when ripping in burst mode. Since synchronization error is no longer a problem with modern drives, it is highly unlikely that this mode will provide any benefit over burst mode.

Burst Mode

Burst mode performs extraction without any error checking. It is handy for discs that do not require re-reading in order to be ripped accurately, especially with drives that cache audio data. It is also handy for discs that trigger re-reading in secure mode but cannot be ripped accurately. When used in conjunction with AccurateRip, or in conjunction with a test CRC to compare with the read CRC in the event that AccurateRip doesn't have data for your disc, burst mode is completely secure.

Drive

Drive read command

(Default: Autodetect read command, Recommended: use the Autodetect read command now button)

This drop-down list allows users to configure which read command to use with the drive to extract audio.


Autodetect read command now

This button will set the proper read command in the Drive read command drop-down list.


"Big Endian" byte order (Motorola)

(Default: disabled)

This option reverses the byte order of the audio data coming from the drive. If the ripped audio is loud static, change this setting.


Swap channels

(Default: disabled)

This setting reverses the stereo channels of the ripped audio. If you find that your drive reverses channels, it is probably due to a two-byte offset which cannot be corrected properly with this option. Try upgrading your drive's firmware or replace it with a different model.


Spin up drive before extraction

(Default: disabled)

This option may or may not improve performance. Enable it if your drive doesn't otherwise operate smoothly or cannot rip the beginning of a track correctly.

Offset / Speed

Use read sample offset correction

Detect read sample offset correction...

Use combined read/write sample offset correction

Overread into Lead-In and Lead-Out

Speed selection

Allow speed reduction during extraction

CD-Text Read capable drive

Gap Detection

The goal with both of these settings is to help EAC get reasonable gap values in a reasonable amount of scanning time. There is no way to know if the values are 100% correct.

Gap/Index retrieval method

EAC offers three methods: A, B, and C; the difference between them is unknown. Method A is a good initial setting, as it is usually fast and provides good results, but on some discs and some drives, B or C might be better.

Detection accuracy

This affects how many times the gap info is read. Inaccurate is one read, so it will be fastest. Accurate and Secure are multiple reads, which will be slower but may perform better on some CDs, especially if scratched or defective.

Background info:

Indexes are track subdivisions. All tracks have index 01 for the main content. Some also have a "gap" (index 00) for a between-song pause (silence or very quiet hiss), or for a non-silent interlude, count-in, or applause. On rare occasion, tracks will have higher-numbered indexes as well.

The start of each track's index 01 is listed in the CD's table of contents, so it is known as soon as the disc is inserted. The other indexes are stored in the disc's subcode, which can be difficult to read correctly. CDs also have slight variances in how and where this info is stored. EAC's Gap Detection settings help cope with these issues.

What are reasonable results?

  • Gaps are all different lengths, and in a range of about 1 to 5 seconds each.
  • Gaps are all exactly 2 seconds each (for a CD-R burned in TAO mode).

What are suspicious results?

  • Gaps are all the same length, and not exactly 2 seconds each.
  • Gaps are all very short—e.g., less than 1 second each.
  • Gaps are all very long—e.g., over 1 minute, or equal to the track length.
  • Gaps extend well beyond the end of a pause/interlude in the music.
  • Gaps get progressively longer.

These are general guidelines; there will be occasional exceptions.

Writer

Writes samples offset

Create Offset Test CD

After Burning Finished

reset drive by ejecting and loading CD-R
only eject CD-R
do not eject CD-R

Drive is able to write UPS/ISRC

Drive is able to write CD-Text

Detect Write Features...

Notes and references

  1. "Uncorrectable" doesn't mean the data is bad, necessarily. In fact, it's normal for at least a portion of data marked uncorrectable to actually be correct; it just wasn't made correct by the C2 system.

External links