19

If I recall correctly, there were lots of variations to implement this scheme. Besides embedding characters in the listing that would reboot, or clear the screen every so often, a particular one I remember worked roughly like this: The listing only consisted of a single CALL. The internal structure of the BASIC program was carefully changed so the listing ...


14

There were multiple ways of protecting the program, including: order of line numbers could be altered to produce: circular listings; missing lines; out-of-order lines; out-of-bounds addressing; the "resume" flag could be set such that any command could cause the program to run again; the start-address for the program could be altered so that another (or ...


12

No, you won't need any 'HiFi' like recorders. After all, these were the very same devices you also used to record your own programs and/or data. While copying from recorder to recorder does always carry a loss in quality, this is of no big influence on a first or second degree copy (*1). The most important factor is volume. It's much the same as when ...


12

SYS is the BASIC instruction to execute a routine written in machine code. There is no more BASIC code to view, the entire game is implemented as a machine code program, and the BASIC only exists as a stub to make it easier to load and run. The best approach to viewing what the code actually does and potentially being able to restore your table (if it is ...


11

In theory, it is fairly simple duplicating a tape. The problem with analog tape-to-tape copies is that sound quality lowers and spurious noises are also copied and more are generated into each new consecutive copy generation. It did not contribute to improve the situation, that later tape copy protection methods/turbo loaders (SpeedLock, Alcatraz...) were ...


11

"Weak bits" are a means of copy protection that generates areas on a disk that read back as random values, without the floppy disk controller actually detecting an error. When copying such a weak bit to a new disk with a standard FDC controller, it will end up as a distinct 0 or 1 depending on the random state that it was read in and never change as long as ...


5

A lot of Commodore 8-bit computer games used a disk that had random-access files on them. This means they were written directly to disk blocks, not via a program, sequential or relative file, which are the three ways Commodore DOS officially supports files. Random files are protected by having the programmer manually mark the blocks as being used. This ...


3

As Jules said, SYS is the BASIC instruction to execute a routine in machine code. Very much like GOSUB. USR is the equivalent of DEF FN. There are 2 ways in which machine code is loaded It is saved with the code. This is great against piracy but it is a pain to modify. Also any minor mod you make might wipe out the assembler. There is a bunch of data ...


1

Perhaps you're remembering "copyright trap": small and inconsequential errors acting as a fingerprint. A product with the same errors must have been copied; if there's no licence, some kind of infringement. I have heard of software with this kind of thing, but don't know of any spreadsheet software. Also some map copyright cases. Related idea is that of "...


1

Although I've only seen such things in games rather than in professional software, the same principle could apply to both: if the program is not altered, it will either behave correctly or refuse to run at all, but attempts to alter the program to bypass the protection will cause other parts of the program to occasionally malfunction in possibly-subtle ways. ...


1

The Commodore 64 was somewhat unusual in that off-the-shelf tape recorders didn't work with it, so you were forced to use the Commodore Datasette unit or later clones thereof. Also tapes copied in a normal twin-deck machine wouldn't load using the Datasette. One solution was a hardware device that plugged into the cassette port and to which two Datasettes ...


1

It's now well publicized how people used to record programs for their machines, from their radio, which were transmitted by radio-stations . So maybe you could have played the program on an audio-speaker, and then used the microphone on a cassette-recorder to copy the tape. That may have bypassed the flutter problem . What about the volume level when ...


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