The PET (short for "Personal Electronic Transactor") was the first computer made by Commodore. Introduced in 1977, it was one of the first "consumer-level" microcomputers (along with the Apple II and TRS-80).

The PET series did not have an operating system in the traditional sense. Instead, they booted directly into Commodore BASIC.

The BASIC programming language built into the PET series was originally purchased by Commodore from a small, obscure company called Microsoft. Interestingly, Commodore was able to purchase BASIC for a one-time fee, meaning Microsoft never collected any royalties from the sale of the countless Commodore computers running it.