The definition of C64/128

The Commodore 64 computer to this day holds the record for being the most successful model of computer ever made with even the lowest estimates being in the tens of millions. Its big brother, the Commodore 128, was not quite as popular but still sold several million units. Both units sported ROM-based BASIC and used it as a default "OS". The C128 also came with CP/M (it was a not-often-exercized option on the C64). In their later days they were also packaged with GEOS. Both are based on 65xx family processors. They are still in use today and boast a friendly and surprisingly active user community. There is even a current effort to port Linux to the C64 and C128 machines.