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-
- U N D E L E T E User Notes
-
- The ST directory structure
-
- Skip this part if you like, but be advised that UNDELETE will not always be
- able to recover your deleted file. This section will help you to understand
- why.
-
- In order to keep track of the files and folders on a disk, TOS records two sets
- of data. The directory itself records the filename (or folder name), the time
- and date of creation or modification, the file length, several special-purpose
- flags (for example, 'read only'), and the location of the first 'cluster'
- belonging to the file. On the ST a cluster is an adjacent pair of sectors, 1024
- bytes.
-
- A second set of data, the File Allocation Table or FAT, has an entry for each
- cluster indicating if it is in use, and if so, where to find the next cluster
- of this file, or whether this is the end-of-file cluster.
-
- When TOS deletes a file, it does not erase the data in the file. Instead, it
- indicates that the file has been erased by replacing the first character of the
- file name with $E5 (i. e., decimal 229). It also modifies the File Allocation
- Table to indicate that the clusters previously belonging to the file are now
- available. It does this by writing a zero in the element corresponding to a
- particular cluster.
-
- When a new file is created, the first available directory entry is used; this
- entry may have been previously used by a file that has been deleted, or it may
- be an entry that has never been used since the disk was last formatted -- if
- there are no '$E5' flags showing. Similarly, the newly created file (or, for
- that matter, a file which is being rewritten, and now requires additional
- clusters) uses the first available (empty -- showing '0') cluster, again
- possibly re-using clusters belonging to, and still retaining data from, an
- erased file.
-
- Usually, if a single file has been erased, and no new file has been written
- (including modified files), it is possible to reconstruct the directory and FAT
- tables unamiguously. However, if several files have been deleted, proper
- reconstruction may not be possible, since their clusters may be intermixed in
- an unknown way. And if write activity has taken place on the disk since the
- deletion, it is unlikely that the file can be recovered, since its directory
- entry probably no longer exists.
-
- How to use Undelete
-
- Before going any further, I must repeat the warning that appears on the opening
- screen of Undelete: ONLY USE UNDELETE ON A DUPLICATE OF YOUR DISK. If you use
- the normal TOS function to copy the entire disk (not individual files), you
- will have a copy of all of the necessary information for Undelete to work
- without putting your original disk at risk.
-
- Also, Undelete works only in medium resolution, and expects to find the subject
- disk in Drive A:, so set up your ST accordingly.
-
- Load UNDELETE.PRG, and place your (duplicate) disk in Drive A. After clicking
- the OK box on the opening screen, select Undelete from the Function menu. A
- first-level (root) directory will be displayed and will show:
-
- 1. Any deleted files which are still in the root directory, and
- 2. All folders in the root directory, deleted or otherwise (deleted folders
- will show up with a '#' in the first character).
-
- Selecting a deleted file or folder displays a dialog box requesting the initial
- character (which has been replaced by the $E5 'delete flag'). After inserting
- the initial character, selecting 'Recover' recovers the file or folder.
- Selecting 'Cancel' will return you to the display of deleted files.
-
- Selecting a non-deleted folder 'opens' the folder, showing all folders and all
- deleted files at the next level within the folder. You may then continue as
- with the root directory.
-
- The 'close' box on the window will always back up the program by one stage. For
- example, if a folder is open, the folder will be closed and the directory which
- included the folder will be displayed. At the root directory, the close box
- backs out of the undelete function so that no function is selected. Selecting
- the close box again terminates the program.
-
- Additional functions.
-
- Since many of the same program procedures are required, a simple directory
- function is a part of the program. It opens and closes folders in exactly the
- same way as the undelete function.
-
- A print function prints whatever directory is presently on the screen. This
- works as a subfunction under both the directory function and the undelete
- function.
-
- A cancel function is also available; it immediately terminates the directory or
- undelete function without terminating the program, and without having to back
- out of several levels of subdirectories (folders) via the close box. The File
- Allocation Table (FAT) is read only on initial selection of one of the
- functions -- undelete or directory -- so a function should be canceled before
- using it to operate on a new disk.
-
-