The Commodore 128, also known as the C128, C-128, C=128, or occasionally CBM 128, is the last 8-bit home computer that was commercially released by Commodore Business Machines (CBM). Introduced in January 1985 at the CES in Las Vegas, it appeared three years after its predecessor, the bestselling Commodore 64.
The C128 is a significantly expanded successor to the C64, with nearly full compatibility. The new machine has 128 kB of RAM in two 64 kB banks, and an 80-column color video output. It has a redesigned case and keyboard. Also included is a Zilog Z80 CPU which allows the C128 to run CP/M, as an alternative to the usual Commodore BASIC environment. The presence of the Z80 and the huge CP/M software library it brings, coupled with the C64’s software library, gives the C128 one of the broadest ranges of available software among its competitors.
The primary hardware designer of the C128 was Bil Herd, who had worked on the Plus/4. Other hardware engineers were Dave Haynie and Frank Palaia, while the IC design work was done by Dave DiOrio. The main Commodore system software was developed by Fred Bowen and Terry Ryan, while the CP/M subsystem was developed by Von Ertwine.
The C128’s keyboard includes four cursor keys, an Alt key, Help key, Esc key, Tab key and a numeric keypad. None of these were present on the C64. Many of the added keys match ones present on the IBM PC’s keyboard and made the new computer more attractive to business software developers. Instead of the single 6510 microprocessor of the C64, the C128 incorporated a two-CPU design. The primary CPU, the 8502, is a slightly improved version of the 6510 capable of being clocked at 2 MHz. The second CPU is a Zilog Z80which is used to run CP/M software.
The C128 has three operating modes. C128 Mode (native mode) ran at 1 or 2 MHz with the 8502 CPU and had both 40- and 80-column text modes available. CP/M Mode uses both the Z80 and the 8502 and is able to function in both 40- or 80-column text mode. C64 Mode is nearly 100 percent compatible with the earlier computer. Selection of these modes is implemented via the Z80 chip. The Z80 controls the bus on initial boot-up and checked to see if there is a CP/M disk in the drive, if there are any C64/C128 cartridges present, and if the Commodore key (C64-mode selector) is active on boot-up. Based on what it finds, it will switch to the appropriate mode of operation.
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