RAM cartridge
Although the NES/Famicom was originally designed to only accept cartridges containing game code and data in read-only memory chips (ROM), both Nintendo and unlicensed third parties released cartridges that allowed games to be played from RAM chips, with data loaded from floppy disks or solid-state flash cards controlled by a small ROM-based BIOS.
Licensed RAM cartridges
The Famicom Disk System's RAM Adapter provides 32 KiB of PRG-RAM and 8 KiB of CHR-RAM. Data is loaded from Mitsumi QuickDisk-format 2.8 inch floppy disks. Games have to be specifically written for the FDS RAM Adapter's memory map, for saving game progress to floppy disk, and if more than 32 KiB of PRG or 8 KiB of CHR data are to be used, for loading additional data from disk.
Unlicensed RAM cartridges
All unlicensed RAM cartridges are primarily designed to run games that originally were released on ROM cartridges. As a consequence, they closely mimic the memory map of ROM cartridges, load the entire game code and data at boot and do not load any data afterwards.
First generation
Early unlicensed RAM cartridges had 128 or 256 KiB of PRG-RAM and 32 KiB of CHR-RAM. They could directly mimic discrete mappers such as UNROM, CNROM and GNROM. Games that originally ran on ASIC mappers such as the Nintendo MMC1 or MMC3 had to be modified to run on these RAM cartridges. If the games used more than 32 KiB of CHR-ROM, or banked it in amounts smaller than 8 KiB, then further modification was necessary, using a technique of caching the most recently-used 32 KiB of CHR-ROM.
These devices historically have been called "copiers" even though none of them actually have the capability to copy a ROM cartridge game to floppy disk. Instead, users had to purchase (or copy) suitable disks from the manufacturer of the RAM cartridge or some other company close to it. Disks were usually specific to a particular RAM cartridge manufacturer and model, with later devices being backwards-compatible only to models by the same manufacturer and the original Bung Game Doctor, often containing detection code to specifically lock-out competing RAM cartridges.
All of these devices are connected between the Famicom main unit and the FDS RAM adapter. The loading process is based on the process of loading a normal FDS game: the original FDS BIOS starts loading a game once a disk has been inserted. Disks targeting these RAM cartridges will contain a file that is loaded by the FDS BIOS to a CPU address unused by the FDS RAM adapter, but that when written to switches in the RAM cartridges's own BIOS and memory map.
- Bung Game Doctor (in 128 KiB and 256 KiB PRG-RAM versions)
- Venus Game Converter
- Front Fareast Magicard (adds 8 KiB PRG-"ROM" banking mode)
- Bung Super Game Doctor (in 256 KiB and 512 KiB versions; adds 8 KiB PRG-"ROM" banking mode and cycle-based IRQ counter)
- Venus Turbo Game Doctor 4M (512 KiB PRG-RAM, adds 8 KiB PRG-ROM banking mode, cycle-based IRQ counter, and real-time saving capability)
Second generation
Later unlicensed RAM cartridges increase the PRG-RAM size to 512 KiB, and the CHR-RAM size to 256 KiB bankable in amounts smaller than 8 KiB. Games still had to be modified to run on these devices.
- Venus Turbo Game Doctor 6M/6+
- Front Fareast Super Magicard. Adds PA12-based IRQ counter. Can also load games from a 3.5 inch MS-DOS-format floppy disk drive (720 KiB or 1.44 MiB), or from a parallel interface connected to a PC with CD-ROM drive.
Third generation
The Bung Game Master has a Xilinx XC3042 FPGA to mimic most ASIC-based mappers, no longer requiring modifications to the games themselves. The mapper-specific fusemap is loaded from floppy disk (called "preboot disk"), just like the games themselves. It can load games from 2.8 inch QuickDisks like earlier models, or from a 3.5 inch MS-DOS-format floppy disk drive.
Fourth generation
Modern RAM cartridges such as the PowerPak or Everdrive N8 are similar to the Bung Game Master in using an FPGA to mimic almost any mapper hardware, but load games and fusemaps from solid state flash cards exclusively. For this reason, they are called "flashcarts".
