Game data

OpenGTA has no game data of its own. It reads the files of your copy of GTA, and also the tables inside the original program (vehicles, peds, weapons, objects, text keys), which it loads from WINO/Grand Theft Auto.exe at run time rather than copying them into its source.

Which GTA

The Windows version from Rockstar's 2002 re-release, distributed as GTAINSTALLER.zip (its README says the game was modified to run on then-current PCs and Windows versions). That release is the complete game, with all three cities. OpenGTA checks its executable: WINO/Grand Theft Auto.exe, 774,144 bytes, CRC-32 a5ca070e.

Rockstar no longer offers the download on its own site. This project doesn't host the game and doesn't link to copies of it elsewhere: use the copy you have.

Two ways to provide it

Either folder works. OpenGTA finds out which one it got.

The installed game

The folder the Windows setup installed GTA to:

GTADATA/      maps (NYC.CMP, SANB.CMP, MIAMI.CMP), styles (STYLE001.G24 ...), MISSION.INI, fonts,
              text, frontend pictures, AUDIO/
WINO/         Grand Theft Auto.exe (and its DLLs, which OpenGTA doesn't use)
Music/        Track1.wav ... Track10.wav (the radio)

The unzipped installer

Unzip GTAINSTALLER.zip and use that folder as it is, no need to run the Windows setup (handy on macOS and Linux). OpenGTA reads the game from the installer's InstallShield cabinets:

data1.cab     the descriptor and most of the game
data2.cab     the rest (Music/Track8.wav is split across the two)
SETUP.EXE, _sys1.cab, _user1.cab, ...   the setup program: not needed

The cabinets are read in place on every run. Nothing is extracted to disk.

What OpenGTA reads

The data files under GTADATA/ (and Music/ for the radio), and the executable WINO/Grand Theft Auto.exe for its tables and checks. It never runs the executable or loads its DLLs. The browser player copies only these into its storage (about 320 MB, most of it the music).

Saves

The player names, scores and options (the original's PLAYER_A.DAT) are kept in gasm's storage, not in the game folder: gasm-run keeps them in its data folder (or --storage-dir), the browser in its site storage. The first run starts from the game's own PLAYER_A.DAT.