It's sort of confusing.
OS 3.1 can run from the usual 3.0 rom chips that most 1200s came with.
The os was expanded with lots of extras in version OS3.5 and again in OS3.9. Both came on CDs due to the extended improvements and enhansments. Both require newer 3.1 rom chips. All of the improvements (especially OS3.9) can tax a stock 1200.
AmigaKit sells 1200s with the option of newer roms (a few more dollars) or you can buy the chips and install them yourself.
