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 MegaDisk Interceptor Ultimate Tool
 Build and write Sega Mega Drive / Master System floppy disks for the
 Mega Disk Interceptor
 Developed by Sebbeug (2026)
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WHAT IT DOES
------------
This tool turns Mega Drive ROMs into floppy disk images for the Mega Disk
Interceptor (a floppy-based copier for the Sega Mega Drive / Genesis) and writes
them to real 3.5" disks using a Greaseweazle USB device.

It can:
  - Put a single game on a disk (it boots automatically).
  - Put several games on one disk (a menu lets you pick which one to run).
  - Split a large game (up to 2 MB) across two disks.
  - Put Master System / Game Gear games on a disk: the console is switched to
    8-bit mode automatically. Mega Drive and Master System games can even share
    the same menu disk.
  - Create system disks (5.5C for the Specify Card, 4.9B for cartridge dumps).
  - Open an existing .img disk image and write it as-is.


WHAT YOU NEED
-------------
  - A Greaseweazle USB device with a 3.5" floppy drive connected to it.
  - Blank 3.5" HD floppy disks.
  - A Mega Disk Interceptor connected to your Mega Drive.
  - The "tools_gw" folder must sit next to this program's .exe. It contains the
    Greaseweazle host tool (gw.exe) and the megadisk.diskdef definition. If this
    folder is missing, the program will tell you it cannot find gw.exe.


THE GREASEWEAZLE STATUS
-----------------------
The status bar at the bottom shows whether a Greaseweazle is connected and on
which COM port. It updates automatically when you plug or unplug the device, so
you do not have to restart the program.


ADDING GAMES
------------
  - Click "Browse...", or drag and drop files onto the list.
  - Accepted formats:
        .md, .bin, .smd  - Mega Drive ROMs
        .sms, .gg, .sg   - Master System / Game Gear ROMs
    Any ROM must be an exact multiple of 16 KB (a 512-byte copier header is
    accepted and removed automatically).
  - The "System" column shows what each entry will run as: "Mega Drive" or
    "SMS / GG". You do not have to convert anything by hand: the file extension
    decides.
  - Drag rows up and down to change the menu order.
  - Double-click a row to rename how the game appears in the on-disk menu
    (13 characters max, A-Z and 0-9).
  - Press Delete to remove the selected game(s).


MASTER SYSTEM AND GAME GEAR GAMES
---------------------------------
Simply add a .sms or .gg file like any other ROM. The disk directory then marks
that entry as an 8-bit game, and the Interceptor starts the console in Z80 /
Master System mode when you run it - the same thing a Power Base Converter does.
Each entry carries its own machine type, so a single menu disk can mix Mega
Drive and Master System titles.

  Master System : works properly (tested on real hardware).

  Game Gear : the games boot, but the colours are wrong - the picture often
      looks almost monochrome. This is normal and cannot be fixed on the disk
      side: the Mega Drive video chip only has the Master System colour mode
      (1 byte per colour), while a Game Gear writes 2 bytes per colour. The
      console therefore reads every half-colour as a full colour. You may also
      see junk around the edges of the picture, because the Game Gear screen is
      smaller than the Master System one.
      If a title exists in a Master System version, use that one instead; the
      other option is a ROM already patched for Master System hardware.

"Tools > Convert Master System / Game Gear ROM" makes a stand-alone converted
file (a 512-byte header followed by the ROM) if you want one for another tool
or for archiving. It is the exact output of the 1995 utility TS-GGMD.COM. For
building a disk with this program you do not need it.


WRITING A DISK
--------------
When games are in the list, a "Write Disk" button appears. Click it and choose:
  - Yes    = write straight to a floppy (no file is left on your hard drive).
  - No     = save an .img file instead (for later use).
  - Cancel = do nothing.

For a two-disk game, the program writes disk 1, then asks you to insert disk 2
and writes it. On the console: launch the game from disk 1; when it asks for
"INSERT DISK 2", swap the floppy and press C.


WRITING AN EXISTING IMAGE
-------------------------
Use "Tools > Open Image to write" to load a .img file. The list shows its
contents in read-only mode and a "Write Image" button appears so you can write
that image to a floppy unchanged. The "System" column tells you whether each
game on that image is a Mega Drive or a Master System title.


SYSTEM DISKS (Tools menu)
-------------------------
  - "Create system disk 5.5C (Specify Card / SRAM)"
        A system disk used with the Specify Card to save and restore cartridge
        SRAM (battery saves).

  - "Create cartridge dump disk (4.9B)"
        A system disk used to dump a physical cartridge to floppy. On the
        console: follow procedure, then press button B (or C).

Both system disks show "NO PROGRAM" when booted - this is normal, they carry no
game, only the loader the console needs.


OPTIONS
-------
  - Verify after write : re-reads the disk to check it after writing. Off by
        default. Note: verification can report errors on track 0 even when the
        disk is actually fine and boots correctly.
  - Pre-erase disk : erases the disk before writing. On by default; improves
        reliability on reused floppies.
  - Drive : which floppy drive the Greaseweazle uses (A or B). Leave on A unless
        your drive is wired as B.

These settings are remembered between sessions.


ABOUT THE DISK FORMAT
---------------------
The images this tool produces are raw 1,595,392-byte disk images. They use a
geometry specific to the Mega Disk Interceptor, so they are not regular PC
floppies and must always be written with the included megadisk.diskdef. A small
"INTERCEPT" boot sector is written so the console accepts the disk.

Mega Drive games are stored in SMD-encoded form (the console's hardware undoes
the encoding while loading). Master System and Game Gear games are stored plain,
without that encoding, and their directory entry is flagged so the console
starts in 8-bit mode.


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