home *** CD-ROM | disk | FTP | other *** search
-
- undel -- a file undelete program This version Jan 93
- ==================================
-
- This program recovers (usually) files that have been accidentally deleted.
- I've tried to make it as easy to use as possible:
- 1. Select the file you want to undelete from the initial file selector.
- The deleted files are shown with the first letter of their name
- replaced by a sigma character, ie "σ". (Don't alter this).
- 2. If undel thinks it can recover the file for you, it shows another
- file selector for you to enter the name of a file to contain a copy
- of your original (deleted) file. It's best if you save this copy
- to another disk.
- 3. Check the copy to see if it is ok. There are special cases when
- UNDEL fails (see below). Also saving new data to the disk may
- overwrite your deleted file.
-
-
- --- DISCLAIMER ---
-
- This is public domain software provided to you by various authors and
- distributers with no guarantee at all. You may use this software only
- if you take absolute responsibility for all consequences of its use.
-
-
- --- DESCRIPTION ---
-
- You don't need to know about file clusters or the disk structure to use
- this program, but here's a quick outline of what goes on.
-
- Formatting a disk divides it up into lots of storage areas called clusters,
- and creates a File Allocation Table to record which clusters contain a
- file's data.
- Saving a file to the disk involves writing 3 separate pieces of information:
- 1. Writing the file contents into clusters somewhere on the disk.
- 2. Writing a directory entry. This contains the file name, size, etc.
- and most importantly where the first cluster of the file is.
- 3. Updating the File Allocation Table (FAT). This is an index of which
- clusters contain the file, and which are free.
-
- When a file is deleted, the first letter of the directory entry is set to
- hex E5 which is displayed as "σ", and the FAT entries are cleared. This means
- the clusters containing the file contents become available for reuse, but
- THE FILE CONTENTS REMAIN INTACT. (Also if new files are saved to the disk at
- this stage, your deleted file could easily be overwritten).
-
- So, we can recover most of the directory entry, but recovering the file
- contents is more difficult because we don't know where to look.
-
- From the directory entry UNDEL finds where the first cluster is, and uses the
- file size to determine how many clusters to find.
- Starting from the first cluster, UNDEL finds as many free clusters as it needs
- to create a file of the correct size. This explains why UNDEL sometimes
- doesn't work: in special cases it might find a cluster that didn't
- belong to the original file, or some of the file's clusters might be somewhere
- else on the disk ...
-
- May you never need to use this program.
-
- Trevor Blight
- 9 Bridge Terrace
- St Ives PE17 4ER
- UK
-
- -------------------------------------------------------------------------
-