After the big success with the Commodore VC-20 the Commodore 64 came out. First it was presented in the USA in 1982, in Europe one year later.
The C64 (picture by Bill Betram)
In the year 1986 Commodore created a new case for the C64. While the motherboard was unchanged, the C64 got a modern look. The C64C was born:
Now the C64 looks like his big brother, the C128, which came out in 1985.
But the C64C selled not for a long time. In 1987 the C64 went back into his old case. But - the motherboard got several changes. Many TTL-ICs were replaced by a special IC. The CPU, VIC-II and SID were replaced by new types. The 64 KB RAM went from eight in two ICs, the ROMs went from three into two ICs. Of course the new C64 was still fully software compatible with the first C64.
In 1991 the motherboard got some additional changes and the C64 came out again with the new case.
There exist five different motherboards with more or less big changes, but they are all compatible to the first one. Any incompatibility would make 100'000s of programs to garbage...
By the way, in 1987 one million C64s were selled in Germany! This means that since his launch in 1982 over 500 C64s were selled per day! Worldwide over 10 million C64 were selled.