The Commodore VIC20 is claimed to have been the first home computer to sell a million units! I can only remember one of my friends owning one of these so I assume most of these where sold in the USA. It is also claimed that the VIC20 was the home version of the PET, with the same processor running at 1Mhz.
The machine had 5Kbytes of RAM and 16Kbytes ROM, it also had a new graphics chip which allowed for a resolution of 176 x 184 with 8 colours, the machine also had a 3 channel sound chip. Storage was done by tape or a separate disk drive could be attached.
Unlike the PET the VIC20 was more commercial and software vendors did write numerous pieces of software for it. I remember the friend who owned one had a great number of games for the machine which if I remember rightly where pretty good quality for a machine with only 5Kbytes of RAM.