Most Atari 8 bit hardware and software remained compatible. All Atari disk drives, printers, and other hardware shared the same interface and should interchange between machines with no trouble. Some software may require more memory than some models (such as the 400 and 600XL) have, but otherwise all software should interchange as well.
One potential problem to note is that of media. Originally, Atari used their own unique disk drive hardware, and in doing so decided not to use an index hole. Most other platforms use soft sectored disks, and expect a hole in the disk to pass a sensor once every revolution. The older Atari drives ignored this hole, allowing the use of hard sectored disks (those with many holes) or a double sided disk upside down in a single sided drive (making effectively no holes). When Atari later switched to industry standard disk mechanisms, the drives expected to find an index hole every revolution. Some proposed solutions are to either copy or modify disks which are causing problems, or to modify the drive to produce the pulse independent of the disk. Supposedly the drive does not use the index information in reading or writing the disk (Atari 8 bit computer mail list).