anti-m/README.md

# Anti-M

Boot any Apple II disk on any Apple II

## What is this?

Many early Apple II games only worked on the original Apple II or Apple ][+.
They refuse to boot on later models, often displaying an "M" error code. This
was due to overly aggressive copy protection; late in the boot process, there
is code that checksums the ROM and reboots if it's not recognized. The games
themselves would work fine if they were allowed to boot past this ROM check.

Other games fail on an enhanced Apple //e, due to subtle differences between
6502 and 65c02 processors. Still others fail on an Apple //c or IIgs, due to
changes in the boot PROM code. Then there are some _very_ early games that
require a 13-sector drive.

Anti-M uses a modified boot PROM that can boot any disk, then controls the
game's bootloader long enough to bypass the ROM check and patch any 6502-
specific opcodes. The result: you can boot any Apple II disk on any Apple II.

## How do I use it?

Boot the Anti-M disk. When it prompts you to insert your original disk, do so,
then press `<RETURN>`. The game should boot normally.

## Which games are supported?

- Beer Run (Sirius)
- Bug Attack (Cavalier)
- Choplifter (Broderbund) (*)
- David's Midnight Magic (Broderbund) (*)
- Dueling Digits (Broderbund)
- Eggs-It (Gebelli)
- Frogger (On-Line Systems) (*)
- Gamma Goblins (Sirius)
- Genetic Drift (Broderbund)
- Hard Hat Mack (Electronic Arts) (*)
- High Orbit (Gebelli)
- Horizon V (Gebelli)
- Jawbreaker ][ (On-Line Systems)
- Juggler (IDSI)
- Labyrinth (Broderbund)
- Lazer Silk (Gebelli)
- Lunar Leepers (On-Line Systems)
- Neptune (Gebelli)
- Orbitron (Sirius)
- Pest Patrol (On-Line Systems)
- Phaser Fire (Gebelli)
- Quadrant 6112 (Sensible Software)
- Red Alert (Broderbund)
- Russki Duck (Gebelli)
- Seafox (Broderbund)
- Serpentine (Broderbund) (*)
- Sky Blazer (Broderbund)
- Space Eggs (Sirius)
- Space Quarks (Broderbund)
- Star Blazer (Broderbund)
- Star Thief (Cavalier)
- Trick Shot (IDSI)
- Zenith (Gebelli)
- all 13-sector disks (e.g. Epyx, Edu-Ware, many others)

(*) later re-released with different copy protection. Only the first release
requires Anti-M.

## Does Anti-M patch my original disk?

No! All patches are done in memory only. If you reboot your original disk
(without running Anti-M), it will fail as usual, because the ROM check or other
incompatible code is still there.

## Can I use Anti-M from a hard drive?

Yes! Copy the `ANTI.M.SYSTEM` file to anywhere on your ProDOS hard drive and
run it with your favorite launcher. Bonus feature: when launching Anti-M from
a hard drive, it will skip the prompt and immediately boot slot 6, drive 1.

## History

v1.1 - 2019-03-16

- support booting 13-sector disks
- support booting disks on Apple //c and IIgs which would otherwise time out
  looking for a boot sector (SpiraDisc, some early EA games)
- bypass a peripheral scan in some games that would hang on some peripherals
  and crash others and require a hardware power cycle in order to reboot
  properly (SpiraDisc)
- support multiple versions of "David's Midnight Magic"
- remove "unsupported game" error, always continue booting
- bypass prompt if launched from hard drive (press the open- or closed-apple
  key on startup to show the prompt)
- minimum requirements lowered to 48K Apple ][+ (still useful for booting
  13-sector disks)

v1.0 - 2019-03-11

- initial release