The Free On-line Dictionary of Computing (30 December 2018):

Commodore 65
Commodore 64DX

    (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.

   (1996-04-07)