Help with assignment - Disk copy protection
gene_zastera
In article , djst...@dragnet.com.au says...
>
>I have an assignment question that reads,
>"What does it mean when a disk is copy protected?"
>There is an earlier question about the write protect notch so I dont
>think it refers to that. I have tried looking this up, but have not
>had any success. Can anyone help with an answer?
>
>Dave Stuart
>djst...@dragnet.com.au
>
I'm no expert on this stuff, but I believe it means that the creator of the disk has
done something to make it difficult (if not impossible) for another person to copy
the disk. I dont know exactly how they do this, but it appears that they can write
to some selected sectors of the disk and intentionally create either a bad sector
or some type of signature that cant be replicated by normal disk copy software.
gene zastera
David Stuart
Bob Morrisette
Copy protected means that you cannot write onto it.
It is the write-protect notch.
Bob Morrisette
Ernie
David Stuart wrote:
>
> I have an assignment question that reads,
> "What does it mean when a disk is copy protected?"
> There is an earlier question about the write protect notch so I dont
> think it refers to that. I have tried looking this up, but have not
> had any success. Can anyone help with an answer?
>
> Dave Stuart
> djst...@dragnet.com.au
Dave,
Disk copy protection was employed by software manufacturers to insure
that each user of their software was truly a registered user and that
the company had been paid for the software.
It was (is) possible for a person to buy a software package and to use
the DOS DISKCOPY function to create multiple sets of the software disks
and give the disks to his/her friends. This deprived the software
company of their rightful income.
Disk copy protection begins with a knowledge of the physical disk
format. The original 5-1/4" , single-sided, 160K floppies had 8 sectors
of 512 bytes on each of the 40 tracks. The 5-1/4" double sided, 360K
floppy had 9 sectors of 512 bytes on each of the 40 tracks. Each sector
on a floppy diskette begins with a track/sector address mark.
Several methods of diskcopy protection were employed. Most of these
methods depended upon the physical characteristics of the disk and the
associated limitations of the DISKCOPY utility. That is, the software
would be shipped on a disk which, in some way, violated the "normal"
disk format and would therefore be mis-copied by the DISKCOPY utility.
1. Write critical data to Track 41. The DISKCOPY program would not
attempt to copy track 41 because iat assumed only 40 tracks. To the
DISCOPY program, track 41 "did not exist". Yet, it is possible to write
a track 41 and to make an install program, shipped with the software,
read the "illegal" track. The stepper motor controlling the head
position on the floppy diskette will quit willingly go to track 41.
2. Use "illegal" track/sector addresses. It is possible to write
sectors 1, 2, 3, 4, 5, 6, 7, 13, and 9 on a diskette. The DISKCOPY
program will bomb with "SECTOR NOT FOUND" because no sector on the track
carries the track/sector address for sector 8. Yet an install program
could specifically read sectors 1 through 8, then create a command to
read sector 13, then read sector 9.
3. The disk has a hole punched in the disk to mark the point in disk
rotation where each track begins. The hole is detected by a photo
transistor that creates a digital signal each time the hole passes under
the phototransistor. The rotation rate was 300 rpm, driven by a servo
motor, and THE SPECIFIC PHYSICAL LOCATION FOR THE FIRST BYTE OF SECTOR 0
(1) COULD BE DETERMINED EXACTLY. A laser could "burn off" the magnetic
coating on the diskette at this point (often on track 39). The result
would be the inability to write a new value to that location. The
installation software would write a new value to the byte and then read
the value. If the read value was the same as the written value, then
that location on the diskette was "normal", i.e., not "burned" and the
installation program, or the executing program would bomb because the
disk was obviously not the original disk which had been "burned" with a
laser.
4. Each diskette drive has a "parameter table" which includes a
definition of how many bytes are written into each sector. A "normal"
diskette had 512 bytes per sector. It was and is possible to write 1024
byte sectors. One early copy protection was to write track 0 and 1, and
4-39 with eight 512 byte sectors and write tracks 2 and 3 with four 1024
byte sectors. The DISKCOPY program assumes only 512 byte sectors so the
program would copy only half of each sector (and four sectors would be
"missing".)
The root of copy protection is to do something different from the
"normal" that the BIOS/DOS will allow. At the BIOS level, Interrupt 13
if you wish to examine the code, The Register value upon entry to the
interrupt are:
AL
AH
DL Drive Number, range 0-3 allowed (Value Checked)
DH Head Numaber, range 0-1 allowed (Value Checked)
CH Track Number, range 0-39 (VALUE NOT CHECKED)
CL Sector Number, range 1-8 (VALUE NOT CHECKED)
AL Number of Sectors, Max=8 (VALUE NOT CHECKED)
AH 0 Reset Diskette System
AH 1 Read status into AL upon return
AH 2 Read desired sectors into memory
AH 3 Write desired sectors from memory
AH 4 Verify the desired sectors
AH 5 Format the desired track
ES:BX must point to the collection of desired address
fields. 1 byte Track Number
1 byte Head Number
1 byte Sector Number
1 byte Number of Bytes: 00 for 128 bytes
01 for 256 bytes
02 for 512 bytes
03 for 1024 bytes
This information comes from the IBM "Technical Reference" part number
6025008, First Edition (August 1981). It fully documented the "open
system" of the IBM PC with full schematics and BIOS source code written
in assembly. Although many changes have taken place, the original
functions remain (for backward compatability).
Just a thought ... FULL knowledge of any computer sytems requires
assembly language abilities and SPECIFIC knowledge of the hardware
chip/functions that perform the I/O functions. I personally recommend
that a software person not limit themselves to higher order language (or
to high level operating system functions)
Hope this helps,
Ernie
Robert Burling-Claridge
Bob Morrisette wrote:
>
> In article 1...@job.acay.com.au, djst...@dragnet.com.au (David Stuart) writes:
> > "What does it mean when a disk is copy protected?"
> > There is an earlier question about the write protect notch so I dont
> > think it refers to that. I have tried looking this up, but have not
> > had any success. Can anyone help with an answer?
>
> It is the write-protect notch.
Well, no, I would say this is more meaning there is some mechanism to
either stop you copying the disk contents, or to make a copy invalid.
There are a variety of mechanisms, some physical (eg physical damage to
a particular part of the disk...) some software (eg "uncopiable" format
files...) Most can be circumvented in various ways. Quite distinct from
write protection, however.
--
Dr Robert Burling-Claridge
Location: Wool Research Organisation of New Zealand, Lincoln, New
Zealand
Email: clar...@wronz.org.nz
Surface-mail: PO Box 4749, Christchurch, New Zealand
"Thought is a dialogue of the soul with itself, and doubt is just a
refusal to deprive either side of a hearing" Plato.
Kevin Barton
Bob Morrisette (wri...@sabu.ebay.sun.com) wrote:
: In article 1...@job.acay.com.au, djst...@dragnet.com.au (David Stuart) writes:
: > I have an assignment question that reads,
: > "What does it mean when a disk is copy protected?"
: > There is an earlier question about the write protect notch so I dont
: > think it refers to that. I have tried looking this up, but have not
: > had any success. Can anyone help with an answer?
: > Dave Stuart
: > djst...@dragnet.com.au
: >
: Copy protected means that you cannot write onto it.
: It is the write-protect notch.
: Bob Morrisette
No, copy protection prevents you from making another copy of the disk.
You can write to it if you wish, but you will ruin the files on the disk which
you were not able to back-up because the disk was copy protected by the softwarecompany. Copy protection used to involve writing between tracks or formatting
the majority of the disk in some non-standard way, then replacing a part of the
DOS with a sort of patch which would only allow the disk to be read when the
program thereon was executed. Simply trying to copy the disk when not executing
the program wouldn't work. There were numerous copy-busting programs out in the
Apple II days for this very reason.
--
Kevin Barton
Electronic Tech.III
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