Source: http://www.megalextoria.com/wordpress/index.php/2015/10/01/commodore-128/
The Commodore 128 was the successor to the Commodore 64. Though many people consider it to be a commercial failure, this is really not the case. Over its life, it sold around 4.5-5.7 million units. As a comparison, sales of all Atari 8-bit computers totaled around 2.5 to 4 million, 8-bit Apple II sales totaled around 5 million and the VIC-20 which was the Commodore 64's successful predecessor sold around 2 million. It's just that the Commodore 64 had a longer commercial life and sold at least 3x that many.
The Commodore 128 was an interesting machine and is arguably the best 8-bit machine ever made. It was really three computers in one. It had its native Commodore 128 mode which is what it is named for, a Commodore 64 mode that was 100% compatible (or so close you would never notice) with the original Commodore 64, and a CP/M mode which was possible due to the inclusion of a secondary Z80 CPU.
Ultimately, the Commodore 128 mode was underused. The first couple years after the 128 was released saw quite a bit of productivity software released (word processors, spreadsheets, databases, desktop publishing, etc) but not much after that. In 128 mode it ran twice as fast as a Commodore 64 and had an 80 column mode (as opposed to the C64 which was 40 columns only) making it ideal for this kind of software. The Commodore 128 would have made a decent games machine as well but sadly very few commercial games were made for it. Developers were hesitant to develop games specifically for the 128 since the Commodore 64 was extremely popular still and every 128 had a 64 inside of it.
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