Undeleting is the process of recovering data that has been deleted from a storage medium, usually the hard drive of a computer. The process can also be done with some e-mail programs.
In most operating systems, deleting a file does not remove the data from the hard drive, but only tags it as unavailable for immediate use. Its location is moved to a folder (or directory ) intended to store deleted files. This folder may have a descriptive name such as recycle bin, trash can, or wastebasket. Undeleting data from this folder in a Windows or Macintosh environment is simple. A file or folder can be moved back to its original location by dragging and dropping the file with the mouse or highlighting the file and clicking "restore". In computers running Unix or Linux , data recovery can involve fairly simple commands and scripts.
After files or folders have been removed from the recycle bin (or equivalent folder), recovery is more difficult. If frequent data backups are made on an external hard drive, CD-ROM, or other storage medium, a recent version of the backup data can be copied back to the hard drive. This is one of the most compelling reasons for making complete, redundant, and frequent backups of all sensitive data. If this has not been done, or if the most recent version of the lost data has changed significantly since it was last backed up, a data recovery program is needed. Several vendors offer such solutions.
In most e-mail programs, the process of undeleting messages is similar to the process in a Windows operating system. However, when the deleted files trash bin (or equivalent) has been emptied, it may not be possible to recover the messages. For e-mail programs installed on a computer, the vendor or a technical specialist in computer forensics can be consulted in regards to lost e-mail messages. For Web-based e-mail programs, the Web site administrator can be contacted.