Keeping old games playable is only half of preserving them. Going back to a favourite to see one scene, one boss or one ending often means replaying tens of hours to get there, and a save skips that.
Some content can't be reached from the game alone any more, either. It needed a second console and a link cable in the same room, or other players nearby over local wireless, as with Dragon Quest IX's visitors and treasure maps. Or it was handed out at an event that ended long ago, like Mew. A save that already has it is the only way left to see it.
Saves do turn up online, but scattered, and the one you find has somebody else's name on it. GSDB keeps them in one place, and where it understands a game's save format it lets you change that before you download.
No. The save editors and the save converter run entirely in your browser. A file you open in them is never sent to GSDB or anywhere else.
That GSDB has worked out that game's save format, so it can show what's in a save and let you change it: the name on it, money, items and so on, depending on the game. Every other game can still have saves archived and downloaded, just not edited. Editors are added one game at a time.
From IGDB, the Internet Game Database: names, covers, release dates and summaries. GSDB keeps its own copy and refreshes it, rather than asking IGDB on every page view. Each game page links back to its IGDB entry.
From the preservation groups No-Intro, which catalogues cartridges and handheld games, and Redump, which catalogues discs. Their lists record every known release of a game (each region, revision and language) with checksums that identify it exactly.
That is what lets GSDB say which release a save belongs to, since a save from one region's version of a game won't always load in another's. Each platform takes its release list from one of the two groups, and its page says which, and when it was last checked.
The archive is being seeded from a collection of saves players shared on GameFAQs over the years, preserved on the Internet Archive. Every archived save says where it came from.
The raw one: the save as the cartridge or the memory card itself holds it, which is what the console reads and what every emulator of it reads. One format per platform, so there is nothing to choose between and nothing to convert before you can use it.
A lot of the saves players shared were written by cheat cartridges instead — DexDrive, Action Replay, CodeBreaker, GameShark, X-Port — and almost nothing made this decade reads those. GSDB doesn't hand one out, because a file you have to identify and convert before it is any use isn't a save you can use. If you have one of those yourself, the converter reads them and turns them into the raw shape, in your browser.
Retro ones: from the NES up to roughly the GameCube, PlayStation 2 and Nintendo DS era. The platforms page lists which are supported today.
Later consoles sign or encrypt their saves and tie them to a console or an account, so a save from one player can't simply be used by another. That puts them outside what GSDB can do.