2016-12-06 (updated 2018-07-07)

MODELS:

[PET 2001 series / CBM 3000 series]
The PET 2001 was announced at the Winter CES in January 1977 and the first 100 units were shipped later that year in October. In 1979, Commodore replaced the original PET 2001 with an improved model known as the 2001-N (the N was short for "New"). The new machine used a standard green-phosphor monitor in place of the light blue in the original 2001. It now had a conventional, full-sized keyboard and no longer sported the built-in cassette recorder. Sales of the newer machines were strong, and Commodore then introduced the models to Europe. The result was the CBM 3000 series. The change to CBM occurred because of a trademark dispute with Philips over the PET name.
Source: Wikipedia

[PET 4000 series / CBM 8000 series]
In 1980, the 4000-series PETs were launched. These used a larger 12" monitor with a redesigned CRT controller and also included the enhanced BASIC 4.0, which added commands for disk functions. The 8000 series was basically a 4000 with 80 columns and slightly different keyboard with smaller (11 key) numeric pad. The 4000/8000 PETs were more explicitly targeted at professional/business use than the 2001/3000. Business customers were the main target for the features of the enhanced BASIC 4.0, and a good selection of prepackaged business software was available.
Source: Wikipedia

[SuperPET 9000 series (SP9000)]
Designed at the University of Waterloo for teaching programming. In addition to the basic CBM 8000 hardware, the 9000 added a second CPU in the form of the Motorola 6809, more RAM and included a number of programming languages including a BASIC in ROM for the 6502 and a separate ANSI Minimal BASIC-compatible BASIC for the 6809. The SuperPET could be purchased finished or as an upgrade kit for the 8000 series.
Source: Wikipedia