ROM Dumping and Preservation: From Cartridge to File

Before a game can be emulated at all, its contents have to exist as a file — and that file has to come from somewhere. Dumping is the process of reading the exact contents of a cartridge’s memory chips and writing them out as a binary image, byte for byte, using hardware built specifically to interface with the cartridge’s physical connector.

What dumping hardware actually does

A dumping device (a dedicated cartridge reader, or a “flashcart” repurposed for reading rather than writing) connects directly to a cartridge’s edge connector and addresses its ROM chip(s) the same way the original console’s hardware would — issuing read cycles across the address bus and capturing whatever appears on the data bus, sequentially, across the chip’s entire address range:

Cartridge ROM chip: address space 0x0000–0x7FFFF (example, 512KB)

Dumper:  set address = 0x00000 → latch data byte → write to output file
         set address = 0x00001 → latch data byte → write to output file
         ...
         set address = 0x7FFFF → latch data byte → write to output file

Result: a .bin/.rom file, byte-for-byte identical to the chip's contents

For simple cartridges this is close to the whole story. Many cartridges are more complex than a single flat ROM chip, though, which is where dumping gets genuinely harder.

Mappers, bank switching, and save RAM complicate the picture

Cartridges frequently include a mapper chip — additional hardware between the console and the ROM that lets a game address far more memory than the console’s native address bus could reach directly, by switching between “banks” of ROM on request. A correct dump has to account for the mapper’s bank-switching behavior to ensure every bank actually gets read, not just whatever bank happens to be active by default at power-on. Cartridges with battery-backed save RAM (a small chip holding in-progress game data, kept alive by a coin-cell battery) add a second, separate concern: the save data is distinct from the ROM program itself, dumped and handled separately, and — for an aging cartridge — often at risk of being lost entirely once its battery finally dies.

Verifying a dump is actually correct

A dump can be silently wrong — a flaky connector, a misbehaving mapper, a single bad read — without any obvious symptom beyond a game glitching in some specific, hard-to-diagnose way much later. Preservation-focused communities verify dumps against known-good checksum databases (No-Intro for cartridge-based systems, Redump for disc-based systems are the two most widely referenced), comparing a new dump’s hash against a previously-verified-correct hash for that exact game and region release. A hash match means byte-for-byte confidence without needing to manually inspect the dump at all; a mismatch flags a bad dump immediately, before it ever gets used.

Why this differs from just “downloading a ROM”

Dumping is the creation of a ROM file from a specific, physical piece of hardware — an act of digitization, in the same sense a library scanning a physical book is digitization. Downloading an already-dumped file from someone else is a completely different act with a completely different legal status: it’s copying an existing copyrighted work, not creating a personal archival copy of hardware you own. The technical process described here applies equally to either framing, but the legal distinction between “I dumped my own cartridge” and “I downloaded someone else’s dump” is real and significant — covered in more depth in BIOS files, copyright, and the law.

Why dumping quality matters more every year

Cartridge-based storage degrades — battery-backed save RAM chips eventually die, and the cartridges themselves are subject to physical wear, connector corrosion, and simple age. Every year that passes, some fraction of the remaining, never-dumped physical copies of older games become permanently inaccessible rather than merely rare. Correct, checksum-verified dumping is the only mechanism by which a game’s exact original contents survive that process at all — which is why the dumping and verification pipeline, unglamorous as it is, sits underneath essentially everything else this category covers.