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#1 |
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Join Date: Apr 2002
Location: Germany
Age: 43
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Question about copy protection
Ok, stupid question here. Didn't know where to put it.
Since I own my Amigas I always wondered how copy protection on disks work. I mean, THOSE ARE SIMPLE DISKS. While copying you read the tracks (or blocks ? cylinders ? whatever...) of the source disk and write them on the destination disk. Simple. They didn't put bad blocks on disks back then, did they ? Can't be the whole clue, as I know that there were different systems of copy protections. So can someone please be so kind to explain it to me after all these years? |
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#2 |
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Join Date: Jan 2002
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Well you kinda answered part of this yourself when you said:
"They didn't put bad blocks on disks back then, did they ?" Well actually yes they did ![]() ![]() This of course is a basic explanation as there are many more types of disk based copy protection out there then you could shake a stick at ![]() |
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#3 |
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Finally things are clearer for me. Thank you for your answer.
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#4 |
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Two of the most common forms of copy protection (trying to be as non-technical answer as I can):
1) Store much more data on a track so they Amiga's floppy contoller can *read* it, but cannot *write* it. Therefore you effectively get non-copyable disks. Better forms of this protection also checked how long it took to read that track or how much was on it - if it was less than expected = copied disk. 2) Normal AmigaDOS disk store data in a certain way. You cannot just write a track of *data* - there is a lot of structure around it. So you need to say, put a "header" after a "certain position" telling me about the "data" I am going to store (checksum, size, etc) - then store the "data" itself in the "position" indicated by the "header". Now, the Amiga's ROM stores the code to be able to read & write AmigaDOS disk format - programmers do not need to know *how* the disk is written to. So wouldn't an ideal copy protection be to store data in a different way than the Amiga's ROM code expects? Think of an Amiga trying to read/copy Atari or PC disks - it can't - without special software that knows the format - and that is just one format! Why not write a custom one? This is really the most common form of copy protection - because without knowing how the data is stored - you cannot read it. So when a "cracker" removes the copy protection - what they are actually doing is looking at the games "loader" to see how the data is stored - then rewriting that loader so that the game can be stored on a format that the Amiga understands - AmigaDOS. Hmm, perhaps (2) was not such a great answer. Basically - there is a lot more stuff on a floppy disk than the "user" data - the data that you actually want to store. You have to also inform whatever reads that "user data" details about that "user data". Okay - tell me if you understood that... ![]() |
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#5 |
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Yes, I DID understand
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#6 |
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Cool
![]() But not "more tracks" - more *data* on *a* track. This form of copy protection is called "longs tracks". You can have a look at the "density" variations here. (look at the graphs) Another interesting one: 3) Unformatted disks are completely *noise* (random) data. Some protections use this by effectively having a noise track somewhere on the disk. The test usually says read track X a number times if each of the reads yields different data then the game is genuine - otherwise it is a copy (if the data is the same). |
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#7 |
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Why does it give random data while reading ? Is this because of the magnetic system of a disk, so there is nothing sorted ? Don't know how to descibe it better so don't laugh :P
I've also had CDs with an empty track on it. You could see it on the CD if you looked at the back, but couldn't read it. Is this variant similiar ? A CD won't give random data, would it ? |
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#8 |
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I don't know much about CD's so I wouldn't really know. However CD's data is clearly defined. A bit is either 0 or 1. So I would not think it would have a noise "state". At least - nothing like magnetic media...
Noise: Basically when a disk has not been formatted, all the magnetic particles are in a transient state, i.e. they do not really form a clear 0 or 1. When you try to read the disk in this state, the floppy logic gets "confused" and gives a best guess estimate on whether a bit read was either 0 or 1. Because of the nature of the magnetic media - this is not a "best guess" at all - it is a completely random guess. Multiple reads will yield different results - because the state of the bits on the disk is not definable by the floppies circuitry. When your format a disk, these particles are pulled into order so clear 0's and 1's can be read as normal. Interesting aside: When a disk gets old, the magnetic particles lose their "charge" and hence revert back to this "noise" state. This is more commonly called "bit-rot" and it mainly cause by the natural magneic fields in the environment - unless you leave your disks next to a speaker of course, then I guess it could be called "accelerated bit-rot"... ![]() |
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#9 |
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Hmmm...better check all of my 400 disks. Damn speakers :laugh. But I know you're right, although it takes a long time till the disks take any damage if you take care of them. Thanks for your explanations. Now I got alot of detailed info.
P.S. You're probably right with the cds. I suspected the same. |
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#10 |
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![]() A long time? Does 15 years count? That is how old quite a few of my collection are! ![]() TDK gives disks 5-10 years reliable life - however I think they are figuring disks will be written to as well as read - which does not really apply here. But your right, most disks will probably last for years to come... However, we have see a worrying number of bad ones at CAPS so far... ![]() |
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#11 |
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only now does the value of TAPES (good ol c64, bless its little cotton socks) become clear
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