CDRW
From CGSecurity
Contents |
CD layout
A CD is composed of several zones
- PCA (Power Calibration Area)
- PMA (Program Memory Area)
- one or more sessions
The SUA (System User Area) is composed of PCA and PMA.
Each session consists of
- a Lead-In Area, containing the session's Table of Contents (TOC),
- the Program Area in which the individual tracks are located,
- and the Lead-Out Area.
A track is composed of
- a pre-gap zone
- audio/user data area
- a pad zone
Each block or sector have an header, the block location is stored in each header.
Recovery of scratched CD-R/CR-RW/DVD
Photorec works well but bad sectors slows the recovery process.
Recovery of fast blanked CD-RW
It's possible to recover data from a quick-erased CD-RW disc without modifying it!
When a CD-RW is fast erased, the PMA, TOC, pregap and the first sectors of your CD-RW are erased. Because the TOC has been erased, CD-RW appears as blank/empty. Because the first sectors has been erased including the headers, sectors 0, 1, 2... can't be located anymore but subsequent sectors can still be found. Unfortunatly, not each OS allows you to easilly access such sector but it works using Linux.
To recover your lost data, run Linux version of Photorec. If CD-RW listed size is 0 or 2048 bytes, the CDROM reader firmware will block further read request, so you have to use another CDROM reader/writer. Start of the recovery is really slow because the first sectors are unreadable but usually after sector 300, data can be recovered, so be patient.
Read of previous cdrom session
With multi-session cdrom, it is possible to delete files of previous session. Because the files are not really deleted, it is possible to recover them. To read files from the first session, run under Linux
mount /dev/cdrom /mnt/cdrom -t iso9660 -o session=0
Return to TestDisk
