MetalGear2 SDMMR 1024K
This page was last modified 10:08, 21 July 2022 by Gdx. Based on work by Grauw.



SDMMR 1024K is a flash card interface developed by MetalGear2. It is based on the SD Mapper/Megaram, an open source hardware design created by Fabio Belavenuto.

The SDMMR 1024K cartridge contains twice as much RAM. And it corrects the main fault of the SD Mapper/Megaram thank to a hybrid mode that allows booting on DOS2 (Nextor) on any MSX computer while being able to run ROMs from MegaRAM. The interface also works on similar ones like 1chipMSX and other clones (OCMs).

The SDMMR cartridge has 2 SD memory card slots (up to 4GB each), so you can put many ROMs or DSKs to run them on your MSX.

SDMMR is an simple interface which has no many advanced feature like the MegaFlashROM+SD 512, Carnivore2, etc. It is therefore not recommended for owners of MSX with a single cartridge slot.

The version manufactured by MetalGear2 have the EDGE connector contacts that are gold plated.

Price: Under €70.

Jgilcas sells his own version too. This one has tinned contacts and its case is made with a 3D printer.


Jgilcas SDMMR 1024K (grey)
Jgilcas SDMMR 1024K (red, blue & pink)
Jgilcas SDMMR 1024K PCB
MetalGear2 SDMMR 1024K PCB
MetalGear2 SDMMR 1024K PCB back

Minimum Requirements

  • MSX1
  • 1 cartridge slot free (primary slot)


  • 2 SD slots (up to 4GB each)
    • FAT 12/16 partitions (up to 256MB in FAT12 and 4GB in FAT16)
  • RAM: 1024kB (configurable as RAM expansion or MegaRAM or both)
  • Flash-ROM: 512kB (that seems now used for the Nextor kernel and SD driver only)
  • Support R800 ROM/DRAM mode on MSX Turbo R and Panasonic MSX2+ turbo mode
  • 3 dip switches to configure the RAM mode


Contrary to what is indicated on the PCB, the function of the swithes would be the following.

  • 1: Hybride mode (512kB Memory Mapper & 512kB Megaram Mapper)
  • 2: Memory Mapper mode only (1024kB)
  • 3: Megaram Mapper mode only (1024kB)
  • 4: Unused


  • ExecROM - Rom loader by Alsoftware for the brazilian MegaRAM cartridge (not 100% Nextor compatible)
  • LOADROM - Rom loader
  • MI.COM - Mapper info by Yukke
  • MEGA16.COM - Megarom with ASC16 mapper loader
  • MEMTEST.COM - RAM of memory mapper tester by Masatoshi Fujimoto
  • ODO.COM - Rom loader
  • Sofarun - UI for DSK, MegaROM and ROM loader by Louthrax
  • TESTMAP.COM - Memory mapper RAM tester by Marteen