The Commodore 128 is a home/personal computer, also known as the C128. It was Commodore Business Machines (CBM)'s last commercially released 8-bit machine. The C128 was introduced in January of 1985 at the Consumer Electronics Show.
The C128 was a significantly expanded successor to the earlier C64, the new machine featuring 128KB RAM (externally expandable to 640KB) and an 80-column RGB monitor output (driven by the 8563 VDC chip with 16KB dedicated video RAM), as well as a redesigned case/keyboard with a numeric keypad. Instead of the 6510 CPU of the C64, the C128 incorporated a two-CPU design. The primary CPU, the 8502, was a slightly improved version of the 6510; its main addition was the ability to run at a 2 MHz clock rate. The second CPU was the Zilog Z80, which allowed the C128 to run CP/M; the machine came with CP/M 3.0, aka CP/M Plus (backward compatible with the CP/M 2.2) and ADM31 terminal emulation. To handle the relatively large amounts of installable RAM, tenfold the 8502's 64KB address space, an on-board MMU chip performed bank switching.
The C128 had three modes of operation: native mode, which ran at 1 or 2 MHz with the 8502 and had both 40- and 80-column text modes available; CP/M mode, which utilized the Z80 and either 40- or 80-column text mode; and C64 mode, which was very nearly 100% compatible with the earlier computer. The C128's native mode improved upon the most criticized attributes of the C64, providing an 80-column display, a reset button, an improved version of the Commodore BASIC programming language with sound, graphics, and disk commands, and much faster disk operations when used with the matching Commodore 1571 (5¼") or 1581 (3½") disk drives.
The Commodore 128D was released in 1987; it was an updated version of the C128 with a detached keyboard and a 1571 disk drive in the same box as the main system unit, providing a sleeker, more professional-looking appearance, much like that of a desktop PC. Inside, the C128D ROMs contained bug fixes, and the 8563 VDC chip was equipped with 64K of video RAM – four times that of the original C128. This permitted the C128D to do higher-resolution graphics with more colors in RGB mode, although very little software took advantage of this capability. The VDC's high-resolution graphics modes were inaccessible from the C128's BASIC and could only be utilized through assembly language or third-party software packages (one such package was the "BASIC 8" extension, available as a ROM chip to install in the C128's extra ROM socket).
Because the C128 would run virtually all C64 software, and because the next-generation, 16-bit, home computers, such as the Commodore Amiga, were gaining ground, relatively little software for the C128's native mode appeared (probably on the order of 100–200 titles). While the C128 sold a total of 4 million units between 1985 and 1989, its popularity paled in comparison to that of its predecessor. This has been blamed on the lack of native software and on Commodore's less-aggressive marketing. Also, when the C128(D) was discontinued in 1989, it was reported to cost nearly as much to manufacture as an Amiga 500, even though the C128D had to sell for several hundred dollars less.