SD Mapper V2 - MSX SD Card & Memory Mapper 512k

What is it?

The SD-Mapper V2 is a dual-slot storage and memory expansion cartridge for all MSX computers. It turns standard SD cards into MSX-compatible mass storage — no floppy drives, no old hard disks, just plug in an SD card and go.

Storage

Dual SD slots: 1× full-size SD + 1× micro-SD

Up to 4GB per card — more than enough for the entire MSX software library

NEXTOR kernel — modern DOS replacement with fast, reliable SD access

FAT12 / FAT16 support — standard partition formats, easy to prepare on any PC

Memory

512KB on-board RAM — switchable between two modes:

MEMORY MAPPER: System RAM expansion for MSX1/MSX2 machines with 64K or less

MEGA-RAM: Load ROM games directly into RAM and run them without the original cartridge

Compatibility

Works with all MSX models — MSX1, MSX2, MSX2+, turbo R

For machines with less than 128K RAM: enable the on-board 512K as MAPPER, otherwise the interface falls back to MSX-DOS1 mode with limited functionality

Design Heritage

Based on the SDMapper project by Flavio — a proven, community-tested open design.

Why did you make it?

Physical floppy disks die. Old SCSI hard drives are unobtainium. SD cards are cheap, reliable, and available everywhere. This cartridge solves the single biggest logistics problem in MSX retro computing: getting software onto the machine without wrestling with 40-year-old storage media.

The 512K RAM expansion is equally essential. Many MSX1 machines shipped with 64K or less — without extra RAM, you're locked out of multi-disk games, memory-mapped software, and modern homebrew. This cart fixes both problems in one slot.

What makes it special?

Two cards, zero hassle — Keep your system disk in one slot, games in the other. Or use micro-SD for daily files and full-size SD as archive backup.

Mapper / Mega-RAM switch — One physical toggle changes the RAM personality. No firmware reflashing, no jumper mess.

NEXTOR instead of MSX-DOS2 — Faster boot, better memory handling, actively maintained kernel.

Slot-efficient — One cartridge slot gives you storage + RAM expansion + DOS environment. Leaves your second slot free for sound carts (FMPAC, SCC) or other peripherals.

Works with SofaRun — Pair it with a uMSX or any MSX2+ system running SofaRun, and browse your SD card game collection with a joystick — no command line needed.

Recommended Setup

For MSX1 with 64K RAM: Enable MAPPER mode → instant 512K+ system, full MSX-DOS2 / NEXTOR functionality.

For MSX2/2+ with 128K+: Enable MEGA-RAM mode → load ROM images directly and run them from RAM.

In the Box

Assembled SD-Mapper V2 cartridge (PCB + 3D-printed or acrylic shell, depending on batch)

Pre-flashed with NEXTOR kernel

SD cards not included — use any 4GB or smaller FAT16-formatted card.