Copy protection

The disk releases used a protection written by Peter K, who signs himself P.G.K. It has three parts: a deliberately altered track 35, a compiled loader that checks for the alteration, and a main program stored in scrambled form. His master disk of tools and notes survives (below), and so does a 2017 account of how to remaster a disk with it, by Marcus.

Track 35

Two programs on the master disk, DOS and DOS-M/L, rewrite track 35 of the game disk. In the master disk’s own words, they change “the track number to track 36”, changing “the header information”, and alter “the density”. A normal 1541 read of track 35 then fails, and that failure is the signature the loader looks for. A standard copier reproduces the readable data but not the damage. DOS is a program compiled with Blitz!, and DOS-M/L is its machine-code helper.

The loader

The first file on a game disk is the loader, named after the game and compiled with Petspeed. It checks track 35 for the expected error, then loads four data files. Marcus records two versions of it. The retail loader has red text and retries indefinitely if the signature is missing. The one on the master disk, MV.NEW.LOAD, has white text and aborts the load instead, and only that one worked for remastering.

The game files

Each game disk carries four sequential files, listed in the master disk’s PROTECT.INFO:

The scrambler

MAKE.CODE3 “will create a scrambled version of the main program”. It initialises its machine code with SYS 2664 ($0A68), asks for the filename twice and refuses to go on unless the two match, then pokes the name into memory from $C001 and its length into $C141 (49473). It asks for the source disk and calls SYS 49472 ($C140), which writes the scrambled CODE3. The note in its header warns that “the system will cold start when finished”.

The hardening notes

Four files on the master disk are notes written as REM lines, apparently meant to be merged into each game’s BASIC:

• LINES.-5.BAS — a five-line header, “written by Mountain Valley, protection by P.G.K”. It disables RUN/STOP and RESTORE, sets the border and background black, prints PLEASE STAND BY., clears $C000–$CFFF, and switches to the upper-case character set (POKE 53272,21).
• RUN/RES.INFO — POKE 808,234 and POKE 792,193 disable the RUN/STOP and RESTORE keys. The first changes the low byte of the STOP vector and the second points NMI at an RTI at $FEC1. Use them, the note says, “as soon as possible at start of any BASIC program”.
• KEYBRD.INFO — POKE 56333,127 turns the keyboard off by stopping CIA 1’s interrupts, and POKE 56333,129 turns it back on. Use it around disk access in BASIC, “else DEVICE NOT PRESENT errors break program if the drive is turned off”.
• DOS.INFO and PROTECT.INFO — the track 35 and file notes quoted above.

The Mermaid and the Crown is the one protected original on this site, kept as a track-level .g64 because a .d64 cannot hold the damage. Read directly, it matches the scheme above. Its first file is a loader named MERMAID, 36 blocks, the same size as MV.NEW.LOAD. The four CODE files follow it. Every sector header on track 35 claims to be track 36. And the directory sector at track 18, sector 1 links to itself.

The other fourteen original disks here are not in this form. Each holds the game as a single program, with no loader and no CODE files, beside the zero-block (C) BRIAN BETTS entry. How they came to be that way is not recorded.