ATR: floppy disk sectors
ATR contains a header and sector data. An emulator or SIO device presents it as a disk. It may hold DOS, a directory and many files, or a program booting without a conventional file system. The extension alone does not identify the DOS used. In a typical DD image, the first three boot sectors are still 128 bytes each. ATR does not preserve every physical feature or protection scheme. Renaming it to XEX will not extract the program inside.
XEX: a binary program
XEX contains code and data segments with their load addresses. It can also set run and initialisation addresses through RUNAD and INITAD. Atari uses a loader to run it; an emulator may open XEX directly. The file can be stored on disk or within ATR. RAM, operating system and BASIC requirements depend on the program.
CAS: cassette recording blocks
CAS stores data and information needed to reproduce a cassette recording. A standard file starts with a FUJI chunk. The baud and data chunks describe speed, data and gaps between records.
WAV and FLAC preserve the audio waveform; CAS preserves the recognised recording structure. CAS extensions also support non-standard signals, but not every tool reproduces them. A turbo tape needs a compatible decoder or emulation of that system.
CAR: a cartridge image
CAR consists of a 16-byte CART header followed by cartridge data. The header identifies the cartridge type, allowing an emulator to determine memory mapping and bank switching. A raw ROM may lack this information, and file size alone does not always distinguish cartridge types.
The format covers both 8-bit computers and the Atari 5200. The correct platform must be selected. Simply renaming ROM to CAR does not add the required header.