It was the successor of the Commodore 64 and could use all the software and a lot of the hardware of the C64 .

One of the main specialities of this machine was the additional Z80 CPU and Video chip, which means that you could attach two monitors. Thanks to the Z80, the Commodore 128 could run under CP/M.

The 128D was the direct successor of the Commodore 128, it had exactly the same characteristics as the 128 except its external case which contained the Commodore 1571 floppy disk unit.

There were two distinct Commodore 128Ds. The 128D and the 128D-CR (for Cost Reduced).
Differences between the 128D and the 128DCR were :
- the 128D was never sold in the U.S. because of all the radio frequency interference it gave off.
- the 128D-CR had a metal case rather than plastic for solving radio frequency problems. This version was sold in the U.S.
- the 128D-CR did not have a cooling fan, although there was a place to mount one.
- the 128D-CR case did not have storage clips for the keyboard.
- the 128D-CR came with 64k of video RAM (for the RGB video chip) rather than 16k for the C128.
- the 128D-CR's printed circuit board was different, and included the drive electronics. So there were 3 CPUs on the board.
- the 128D-CR came with bugfixed (1986) ROMs in two 32k x 8 chips instead of four 16k x 8 ones.
- The internal drive's ROM was different from the original 1571 ROM in two ways: it was bugfixed, and had changes for the new support chips. The bugfixes were bigger than the changes for the new hardware.
- 128D-CR CPU RAM was in four 64k x 4 chips rather than sixteen 64k x 1 ones.
- the 128D-CR did not have a carrying handle.