Wiping Data Area of specific file
We discussed about the data wiping programs which wipe the data of unallocated space of the disk or wipe the entire disk. But if user is willing to wipe the data every time when he deletes the data, it may be a time taking process to wipe the entire unallocated space of the disk.
We need this type of data wiping programs to wipe the data area only occupied by that particular file. For doing this, we get the help from FAT and Root directory entries, to find the data area occupied by that particular files.
Even in case of floppy, if the data is not fragmented, we can do so only with the help of Root directory information. The Following table shows the information stored by a root directory entry with 32 bytes, for any file:
Offset |
Size |
Description |
00H |
8 Bytes |
Filename (Also see the next table for the special meaning of first character of file name) |
08H |
3 Bytes |
Extension |
0BH |
1 Byte |
File attributes(See The Table Of File Attributes) |
0CH |
10Bytes |
Reserved |
16H |
2 Bytes |
Time Created or Last Updated (See Date–Time Format Table) |
18H |
2 Bytes |
Date Created or Last Updated (See Date–Time Format Table) |
1AH |
2 Bytes |
Starting or First cluster of file
(The value 0000H is used in Parent Directory ('..') entries to indicate that the Parent Directory is the Root Directory) |
1CH |
4 Bytes |
File size in Bytes. |
As we see in the table of contents of root directory entry, we are capable to find the starting and ending cluster of the files. The first Byte of the filename may also contain some important information about file. The information given by this byte may be one of the given below:
First Character of File Name |
Value |
Meaning |
00H |
Indicates that this directory entry is unused. |
05H |
Indicates that 1st character of filename is character E5H But actually the file has not been deleted. (See the Meaning of E5H) |
E5H |
The file has been Erased and this directory entry is a deleted file’s directory entry. The data area previously occupied by that file is now free for allocation for another new file. |
2EH |
This is a Sub-directory. The cluster number field of this entry will contain the cluster number of the directory. |
2EH 2EH |
Two 2EH in a directory entry indicate the parent directory entry of a Sub–Directory. The cluster number of this entry will contain the cluster number of the parent directory of this directory. The cluster number will be zero 0000H if the parent directory is root directory. |
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