(Or Commodore 64DX, C65, C64DX) The last 8-bit computer designed by Commodore Business Machines, about 1989-1991. The C65 boasts an ugly collection of custom integrated circuits which makes even the Amiga hardware look standard.
The core of the C65 chipset is the CSG 4510 and CSG 4569. The 4510 is a 65CE02 with two 6526 CIAs. The 4569 is equivalent to a combination of the 6569 VIC-II and the MMU of the Commodore 64. The C65 also has a DMA controller (Commodore's purpose built DMAgic) which also functions as a simple blitter, and a floppy controller for the internal Commodore 1581-like disk drive. The floppy controller, known as the F011, supports seven drives (though the DOS only supports 2). The 4510 supports all the C64 video modes, plus an 80 column text mode, and bitplane modes. The bitplane modes can use up to eight bitplanes, and resolutions of up to 1280 x 400. The palette is 12-bit like the Amiga 500. It also has two SID's (MOS 8580/6581) for stereo audio.
The C65 has two busses, D and E, with 64 kilobytes of RAM on each. The VIC-III can access the D-bus while the CPU accesses the E-bus, and then they can swap around. This effectively makes the whole 8MB address space both chip ram and fast ram. RAM expansion is accomplished through a trap door slot in the bottom which uses a grock of a connector. The C65 has a C128-like native mode, where all of the new features are enabled, and the CPU runs at 3.5 megahertz with its pipeline enabled. It also has a C64 incompatibility mode which offers approx 50-80% compatibility with C64 software by turning off all its bells and whistles. The bells and whistles can still be accessed from the C64 mode, which is dissimilar to the C128's inescapable C64 mode.
Production of the C65 was dropped only a few weeks before it moved from the Alpha stage, possibly due to Commodore's cash shortage. Commodore estimate that "between 50 and 10000" exist. There are at least three in Australia, about 30 in Germany and "some" in the USA and Canada.