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Information - Undel

GenreTape / Disk / Cartridge UtilityYear1996
Language[unknown]PublisherST Format
Developer[n/a]DistributorFuture Publishing
ControlsMouseCountryUnited Kingdom
Box / InstructionsEnglishSoftwareEnglish

Blight, Trevor

LicensePD / Freeware / Shareware
SerialST TypeST, STe / 0.5MB
ResolutionMedium / HighNumber of Disks1 / Double-Sided
Dumpdownload atari Undel Download / MSAMIDI

Instructions - Undel

                 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 "å". (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 "å", 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

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