The 128D model:

The 128D is the direct successor of the Commodore 128 : it has exactly the same characteristics as the 128 except its external case which contains the Commodore 1570 floppy disk unit.

Actually there are two distincs Commodore 128Ds : The 128D and the 128D-CR (for Cost Reduced).
Differences between the 128D and the 128DCR are :
- The 128D was never sold in the U.S. because of all the radio frequency interference it gives off.
- the 128D-CR has a metal case rather than plastic.
- the 128D-CR does not have a cooling fan, although there is a place to mount one.
- the 128D-CR case does not have storage clips for the keyboard. - the 128D-CR comes with 64k of video RAM (for the RGB video chip) rather than 16k for the C128.
- the 128D-CR's printed circuit board is different, and includes the drive electronics. So there are 4 CPUs on the board.
- the 128D-CR comes with bugfixed (1986) ROMs in two 32k x 8 chips instead of four 16k x 8 ones.
- The internal drive's ROM is different from the original 1571 ROM in two ways: it is bugfixed, and it has changes for the new support chips. The bugfixes are bigger than the changes for the new hardware.
- 128D-CR CPU RAM is in four 64k x 4 chips rather than sixteen 64k x 1 ones.
- the 128D-CR does not have a carrying handle.

 
NAME   C 128 - C 128D
MANUFACTURER   Commodore
TYPE   Home Computer
ORIGINE   U.S.A.
YEAR   1985
BUILT IN LANGUAGE   Basic
KEYBOARD   Complete full-stroke keyboard with separated numeric keypad
CPU   8502 + Zilog Z80
SPEED   1/2 mHz (for the 8510), 1.022 MHz (for C64 mode)
COPROCESSOR   SID (sound) & VIC-II (video)
RAM   128 KB (expandable to
VRAM   16 KB
ROM   48 KB (with
TEXT MODES   40 x 25 / 80 x 25
GRAPHIC MODES   several, most used : 160x200 / 320 x 200 / 640 x 200
COLORS   16
SOUND   3 voices / 6 octaves
I/O PORTS   RGB, Video Composite, Joystick (2), Cardridge, Tape, User Port (RS232 compatible), TV, serial
OS   C128 mode, C64 mode or CP/M