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Altirra. A new Atari 8bit Emulator

Altirra is designed with emulation quality in mind, sometimes over speed and polish. It's designed as a system emulator and debugger instead of a games machine, so there is some setup involved. There is a README file in the archive, but here are some quick tips:

First: Software. you need some actual 8-bit Atari (not Atari ST!) software to run. If you don't have any, it'll be a pretty boring experience. I can't give this to you for various reasons, but there are freely available demos, and if you have converted your Atari software to disk images for other emulators, those will work too. Specifically, disk images are supported in ATR, DCM, ATX, and PRO formats; some simple cartridge types are also supported, and you can directly load Atari executables as well (.obx/.xex).

Second: kernel ROMs. Altirra has an internal kernel that can be used to run Atari software, and thus you can run demos, games, and productivity software without needing any Atari ROM images. However, this kernel is reimplemented from scratch, and has some compatibility problems. Therefore, you may want to consider hooking up real kernel ROM images, which will greatly increase Altirra's software compatibility. I'm afraid I can't offer these for download, but if you have downloaded ROM images from your Atari, Altirra uses the same format and filenames as most other popular Atari 8-bit system emulators.

Third: compatibility. Altirra is designed to emulate the actual Atari hardware as closely as possible. Its compatibility has been increasing over time, and at this point it should run most software correctly. However, there can still be problems, some of which may be emulation bugs, and some of which are related to hardware emulation settings. Tips:

  • Disable BASIC (unless you're actually running a BASIC program).
  • For older games, use 800 hardware and 48K RAM, and the OS-B kernel.
  • For newer games, use XL hardware and 128K RAM (XE), and use the XL kernel.
  • For demos and games written in Europe, use XL hardware/kernel, 320K RAM, and PAL.
  • If you don't have kernel ROM images, use the HLE kernel instead.
  • Use Input Joystick or Shift+F1 to toggle the joystick, which uses the arrow keys and the left control key.

http://www.virtualdub.org/altirra.html