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COVERUP.DOC
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1990-07-21
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CoverUp.DOC
Copyright (C) 1990 Jay Vanderbilt
CoverUp.COM 10819 bytes
Erases all data in free space on a disk
Erases the data in a cluster beyond the file end
Overwrites all data in erased directory entries
Reports the number of bytes in bad sectors
[Does not deal with data in clusters marked bad]
Preserves time, date, and all attributes of files
Sets errorlevel for use in batch files
Reports on progress as it runs
Exits on start-up if problems detected
Exits after clean-up on all disk errors
Should handle any standard hard or floppy disk
Requirements DOS 2.00+ 192k free memory
Speed 1.2meg floppy, 72 files, 720k, 3 directories 1 m 28 s
360k floppy, 24 files, 240k, 1 directory 35 s
32meg hard, 980 files, 23meg, 18 directories 4 m 6 s
[Times for 12 mhz AT Clone MS-DOS 3.30 VERIFY = OFF
Your times will vary.]
Erases with 0f6h for data
Meaningless name for directories
TABLE OF CONTENTS
Bug Reports.........................................................2
What CoverUp Does And Why...........................................3
WARNINGS............................................................4
How To Use The Program..............................................5
What Is Happening While The Program Runs?...........................6
Program Speed.......................................................6
Hard Disks..........................................................7
Unusual Drives......................................................8
Error Messages......................................................9
Message In A Box...................................................10
Revisions..........................................................11
CoverUp Version 1.01 Copyright (c) 1990, Jay Vanderbilt
CoverUp may be freely distributed provided that it is unaltered and
that the complete, unaltered documentation is included. CoverUp
may not be sold or included in any commercial package without
written permission.
CREDITS
The program was originally named and specified on BIX by Roedy Green.
Roedy Green, Robert Babcock, and David Holm among others on BIX
helped at various stages with the design and testing. All mistakes,
bugs, and design errors are entirely my own.
-2-
A Special Plea
(From The Heart Of Anyone Who Has Written Freeware)
Programmers who write and distribute freeware do not have the
resources to test every possible combination of equipment and software;
they must rely on cautious programming to avoid fatal errors and user
feedback to find and fix special cases. Consider the record some
of the biggest software houses have with compatibility problems.
Consider the disdain with which they treat bug reports. Remember that
the people who write the programs you get for free always want to hear
from you.
If you have a problem, let me know. If you like the program,
let me know. If you hate it, let me know. If it isn't what you
wanted, let me know. Whatever you have to say, I want to hear it.
Report bugs and make suggestions for improvements to:
Jay Vanderbilt
3 Calvin #1
Somerville, Ma 02143
617-776-5792 (reasonable hours please)
j_vanderbilt on BIX
-3-
What CoverUp Does and Why
This program erases everything from a floppy disk except the
structure of the disk (directories and file allocation table) and the
actual data in the files. This is every bit as useless as it sounds
99% of the time. However, when you send a disk out to be duplicated
or to a customer you might be surprised to find what can be lurking
unnoticed beyond the ends of files or in the unused areas of the
disk.
What DOS Does When It Erases and Copies
When DOS erases a file it does not touch any of the data; all
it does is mark the directory entry and the disk space as available.
Until that space is overwritten the original file is still there and
can be read by anyone with a file uneraser or disk browser. When DOS
writes to a file it only allocates space in discrete chunks (clusters).
The unused space at the end of a cluster contains whatever was there
before the file was written and that also can be read by anyone with
a disk browser. When DOS writes or copies anything less than a
full sector (512 bytes, the smallest unit the disk drive deals with)
it does so through its own internal buffers. This includes the end of
any file that is not an exact multiple of the size of a sector. The
sector will be filled out with whatever happened to be in the buffer
from the last time it was used. It is also possible, though unlikely,
for data to be concealed in clusters marked bad. Because the program
avoids using direct writes, CoverUp ignores this possibility.
Most of the time this means nothing. Nonetheless it could be
embarrassing to send out half your mailing list or the save files
for Zork with a disk of data for your customers. People using disk-
browsing utilities could be confused by random gibberish at the ends
of programs. If you need to do something about it CoverUp is for
you.
-4-
WARNINGS
Please read this section before you use the program. It's
important. The program checks for dangerous conditions as well as
it can, but it can't do everything. With a little care you should
never have a problem.
NEVER use CoverUp on the only copy of a disk!
This is so simple and obvious that it has to go first. It's too
easy to forget how hard it is to recover the original of a file, and
how easy it is just to make another copy if something goes wrong.
NEVER use CoverUp on the original copy of copy-protected software!
This is a corollary of the first warning. A copy-protection
method may work by hiding data in unusual places or modifying the disk
layout. CoverUp will not remove the protection, but it may destroy
the hidden data and make the program useless. A legitimate copy of
the software which has been installed on another disk will not be
affected by CoverUp.
NEVER use CoverUp with drive-aliasing active (JOIN ASSGN or SUBST)!
ASSIGN, JOIN, and SUBST are utilities provided with DOS for use
with old programs that insist on having files on particular drives
or do not work with directories. They work by faking the drive or
directory name to the operating system. These, an