With CD-RW disks it is possible to erase them.  Once erased, logically they look like a new blank disk.  Physically though, one can normally see that the disk has been written to by the different colour on the data side of the disk.  This is a forensics only option.

Most programs will treat an erased disk as just that, and there is no way to recover the data.  CnW software does have a way that normally works to in effect unerase the disk, and make the disk readable again.

There are two modes to disk erasing, a quick erase, and a full erase.  A quick erase just sets all pointers on the disk, in hidden areas to make it look like a new disk. This mode can be recovered. A full erase will overwrite each sector, and this means that data can never be recovered.

Recovery of erased CD-RW disks

A problem with an erased CD-RW is that it looks just like a blank disk, and it is impossible to determine what has happened to it without doing the unerase process.  It must be noted that the unerase used in CnW does actually write to the disk and so potentially it could damage a disk that has failed, but not due to being erased. It should therefore be treated with caution, but at the same time it may be the only option.  This function, belived to be unique on commercial user software, can be slightly problamatic, but it does normally produce the desired results, although occasionally multiple attempts may be required.

The Wizard on CnW will highlight disks that are possibly erased. In these cases, the Manual Recovery mode should be entered, and on the CD recovery options menu there is a button for Unerase disk, which is only enabled when a blank disk is detected. When the function is selected, a new screen is displayed with many options on. As mentioned above, the configuration of the disk before erasing can normally only be guessed at, and so the unerase may need to be done in different ways until the correct combination is found.

It is necessary to try and replicate how the disk was written first of all.  Some combinations will display the error message "Error setting SelectMode" when the Unerase button is pressed.

A good starting point is to use the variables shown above. The one very important parameter is the Data Block Type. If the incorrect value is chosen, then the data on the disk will be 8 bytes out of sync.  However, there is a test at the end of the unerase that will ensure the correct value has been entered.  If the value was wrong, then it will be necessary to Blank CD and select a different Data block type before doing a new Unerase function.

Sometimes, there is a 'false' error message saying that the unerase has failed.  Before doing anything, the disk should be tried, with the view function and an attempt to read sectors above 16 (0x10) should be made.  If this works, then a recover functioin can be tried.