31 votes
Accepted

How does "bit-slip" copy protection work?

The Apple II reads disk tracks as a continuous stream of bits. To make sense of the data, it's necessary to figure out where individual bytes start. This is done with self-sync bytes. Standard self-...
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  • 7,421
27 votes
Accepted

How did "full memory" Spectrum tape copiers work?

These programs usually had a mono-color background with very little text. By setting the color of the screen as "black ink on black paper" or "white ink on white paper", it is possible to relocate the ...
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  • 1,203
23 votes
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Which software was the first to use copy protection?

I couldn't say which one was the first but there were early efforts in the 1970's and 1980's Encrypted roms Arcade games were often hacked so ROM encryption was developed, so if the board was re-made ...
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22 votes

How did "full memory" Spectrum tape copiers work?

There are multiple techniques used by tape copy programs to be able to copy large blocks of data. By large we mean close to the whole RAM capacity (48 KiB) or even more! Using maximum of the ...
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22 votes

How did Apple II BASIC programs protect against listing?

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 ...
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  • 20.9k
20 votes
Accepted

Disk copy protection schemes for Apple II

That question is kind of overly broad, as it essentially asks to explain all ways a floppy image can be composed and written - which is next to infinit. A short search may turn up quite a lot of hits. ...
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  • 166k
18 votes

How did Apple II BASIC programs protect against listing?

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; ...
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  • 1,054
16 votes

Copying tapes "back in the day"

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 ...
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16 votes

Weak bits on floppy for copy protection

"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 ...
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  • 27.4k
16 votes

Which software was the first to use copy protection?

One of the earliest would likely have been Microchess 2.0 for the Apple II, shipped on cassette in 1978. Andy McFadden's Early Copy Protection on the Apple II article has the details.
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  • 17.1k
15 votes

How was Prince of Persia "better/faster" with RWTS18?

The assertion that 4x4 is faster is false, it's easier, yes, but not faster. RWTS18 could read the entire track in one revolution so it is the fastest. I know that 4x4 and 6x2 were also capable of ...
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14 votes
Accepted

How can I view BASIC code hidden by SYS?

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 ...
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  • 12.2k
14 votes
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What's the point of the CPS-2 suicide battery?

This was an anti-piracy measure. If a "bootlegger" wanted to duplicate the board, they would only have access to encrypted ROMs, thus making it impossible to reproduce the arcade board with ...
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  • 56.5k
13 votes

Was the Amstrad's file protection considered secure in 1985?

Secure? No, but much more so than protected BASIC programmes on tape, which merely had a single field set in the tape header that triggered the run once then NEW behaviour. It would definitely have ...
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  • 17.1k
13 votes

Why does changing a DOS/Windows EXE cause it to not run?

If you change the lengths of strings in a binary, or indeed move any part of a binary around in any way, then you’re likely to break it: offsets to the data (and code) that the program expects to find ...
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12 votes

Copying tapes "back in the day"

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 ...
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  • 166k
10 votes
Accepted

How was Prince of Persia "better/faster" with RWTS18?

Less disk swapping, but also faster loading. Much of the performance improvement in Apple II fast DOS implementations (including ProDOS) was due to less latency between reading sectors - and this ...
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10 votes

Were commercial Amiga floppy disks shipped with write protection?

I bought a lot of original games and the floppies were always write protected from the start. I also remember the message that appeared a lot in manuals: ALWAYS KEEP YOUR DISKS WRITE PROTECTED (just ...
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10 votes

Disk copy protection schemes for Apple II

I remember Locksmith, too, and I actually still have it on floppy somewhere. There was a wide variety of protection schemes, from "let's use non-standard code for GCR address and data marks" ...
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  • 20.9k
8 votes

Disk copy protection schemes for Apple II

You can find some detailed descriptions below. There are two primary classes of protections that Locksmith could not duplicate - "E7" and "weak bits", the first of which was used ...
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  • 1,054
7 votes

Was the Amstrad's file protection considered secure in 1985?

I'm not familiar with that system, but if users had the ability to protect their own files, then no it was not secure. If you can protect your own files (with known contents) then you have easy ...
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  • 11.3k
7 votes

How did "full memory" Spectrum tape copiers work?

Assuming a program consisting of a unique big block of 49152 bytes (the whole RAM space). A routine that may be used for a copier to copy this block would sit at the top memory, say at address 64000 ...
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7 votes

Why does changing a DOS/Windows EXE cause it to not run?

Adding or removing some text has the effect that things coming later in the EXE file are now found at a different absolute location, machine code as well as the EXE file format rely a lot on absolute ...
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6 votes
Accepted

Advantages to installing a parallel port in a C1541-family drive other than speed

Nibblers that are utilizing opencbm on a PC need a faster-than-stock connection to read the GCR encoding in real time. There are a couple of solutions, the most common of which requires a ZoomFloppy. ...
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  • 1,053
6 votes

Was the Amstrad's file protection considered secure in 1985?

No, it wasn't considered really secure. In fact several programs existed at the time, including small "type-ins" available in magazines for removing that exact protection. There are some of them ...
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6 votes

How can I view BASIC code hidden by SYS?

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 ...
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5 votes
Accepted

Where can this "boot.B" file be coming from on this Spectrum TR-DOS disk image?

I think possibly your emulator is fooling you. Per this FUSE feature request, leading to this patch in particular and this commit, FUSE synthesises a boot.b and adds it to the disk directory if you ...
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  • 32.2k
5 votes

Were commercial Amiga floppy disks shipped with write protection?

As Jean-François Fabre already points out quite a lot of data got lost by overwriting the wrong disk. So reminding users to write protect was a well needed advice. No matter if official documentation ...
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