.CAR File Format

Introduction

A .car file is a cartridge for the Atari 8-bit computers (400, 800, XL, XE) or for the Atari 5200, in the format the Atari800 emulator introduced and the other emulators adopted. Raw dumps of these cartridges are just the ROM bytes, so nothing says how a big one is wired; the .car file adds a 16-byte header that names the cartridge type, and with it the size and the bank-switching scheme. The signature is the four letters CART.

The explorer shows the header, tells whether the type is known, whether the ROM has the size the type needs and whether the checksum matches, shows the 8-bit cartridge trailer (start address, present flag, option byte, init address) for the plain and XEGS types, and disassembles the ROM for the types whose address layout is simple. For the many types with bank switching it lists the type and does not disassemble. The full list of the types is on Cartridge types.

Structure

No real .car file was available while the viewer was written: it was tested on built files, and against the table of types in the atari5200 emulator on this machine.

Raw cartridge ROMs

A raw 8-bit cartridge ROM (.rom, or .bin) has no header. The atari5200 emulator recognises an 8 KiB or 16 KiB one by its last six bytes (start address, a zero byte at $BFFC, an option byte with bit 2 set when the start address is used, init address), the same trailer the viewer shows for .car files of the plain types. Such a file is not claimed by the explorer: use a .car name, or “Read as”.

Not described

Known, not yet covered

• Viewer: the bank layout of almost all of the 114 types: only the plain ones (types 1, 2, 4, 6, 16, 19 to 21, 57 to 59) and the XEGS ones (12 to 14, 23 to 25) are disassembled. For the rest the table says what is known. See Cartridge types.
• Reference: types above 160, and any between 113 and 158: the list this page uses stops at type 160 because the source it was taken from does. Newer lists may define more.
• Reference: the checksum is described as the sum of the ROM bytes; the emulator on this machine reads it but never checks it.

Unknown

• Reference and viewer: no real .car file was available. The types list comes from one emulator’s table (which in turn cites atari800’s cart.txt; that file is not on this machine to compare).

Other Atari cartridge formats

These are separate formats, not variants of one: the hardware, the file and the pages differ.

• Atari 2600 ROM image (A26) – raw ROM of the 2600, bank switching chosen by hand
• Atari 7800 ROM image (A78) – a 128-byte header, then the ROM
• Atari 5200 ROM image (A52) – raw ROM with a header at its top
• Atari cartridge file (CAR) – a 16-byte header and a type number, for the 8-bit computers and the 5200

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