Finally, way back at the end of memory, we come to the Operating System itself, stored in a 10K ROM cartridge (inside your computer). This OS ROM includes not only the program for the Operating System (yes, the OS is just another program), but also the floating point package, the data for the Atari character set, the device handlers, and various vectors.

As I've mentioned throughout the book, there are two versions of the OS as of this writing. Version "B" includes some changes to get rid of a few of the bugs that appeared in version "A." These changes come mainly in SIO and the interrupt handler routines. The addresses I'll be giving below will be for version "A," since it is the best documented. You should see Appendix Five on OS changes to determine which locations will not be the same in version "B." How do you know which version you have? If PEEK(58383) equals zero then you have version "B."

If you need more specific information on the locations and routines described next, I suggest you study the appropriate parts of the OS Listing. It is well commented and relatively easy to understand.

All locations in the OS are PEEK only.

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