Commodore 128

C128 is the short name of the home computer Commodore 128 It was designed as a successor to the C64, but should also satisfy professional demands. In January 1985, the device was unveiled at CES in Las Vegas. The C128 was the last ready for production and Commodore 8- bit computer.

In addition to the native C128 mode he has two additional modes: the C64 mode in which he is almost one hundred percent compatible with the C64, and the CP / M mode, in which the processor of 64/128-Modi, the 8502, is responsible for input and output operations and for the CP / M compatibility of a Z80 Zilog used. In C64 mode is accessed by entering the BASIC command " GO64 " after booting the C128 or holding down the Commodore key during power up. In the CP / M mode is accessed by inserting a CP / M disk and a cold or warm start or the BASIC command BOOT.


Technically the C128 is based on the C64, but still has additional elements:

  • The Z80B CPU ( de facto 2 MHz) for the CP / M mode;
  • The graphics chip VDC, which has a higher resolution (80 characters in the horizontal) and many other opportunities (flashing, underlined character, 2 character sets at the same time, graphical mode, ...), which has not yet exploited only partially. In addition, he has a standalone video memory of 16 ( later even 64) KB. The disadvantage is that it can not replace the old 40-character VIC II video chip, but only supplement. In addition, access to the separate memory is not possible directly to the CPU, which read and write requests have been extremely slow and, therefore, the chip is hardly suitable for the game program. It can only be used in conjunction with a C128 monitor or an IBM CGA monitor, use a C64 monitor or TV is only possible by means of special, Commodore not offered cable and only with black / white image. A colored image is either only with tricks or can not be represented according to the TV;
  • An MMU ( Memory Management Unit ), which can theoretically manage up to 1 MB of memory ( the real existing chips but only 128 KB) and also is responsible for switching between the different modes of operation;
  • 128 KB of memory, divided into two banks of 64 KB, with a bank for BASIC programs, the other is used for variables;
  • An extended keyboard with numeric keypad and comfortable cursor keys.

When CPU is used for 8502 - a modified 6510 chip, which can be clocked almost twice as fast in the C128 mode (about 2 MHz, the exact value varies due to the different television standards between the American and European C128 ). However, the 40-character video chip, access to the main memory is denied to this end, so that it can activate the 2- MHz mode only unused 40-character display. VDC is unaffected by the 2- MHz mode, as it already does not access the main memory; a 80 - character representation is thus furthermore possible. If one wants to use the higher speed in the 40-character display, it is possible to activate the 2- MHz mode only in the image areas, in which the 40- character video chip does not need to access the main memory. In this way, one can accelerate from about 1 MHz to about 1.3 MHz effectively the C128 after all. An example of this is the C64 game " Uridium " that in C64 mode of the C128 is a bit more sprites than on a C64. For GEOS 128, there was a utility that also took advantage of this trick in 40 - character mode to speed GEOS by about 30 %.

Operating Systems / BASIC

The operating system and programming environment in a Commodore BASIC a Commodore greatly expanded version of Microsoft BASIC 2.0, which was already used in the VIC-20 and C64 is version 7.0. The BASIC can be found in the ROM of C128 and be available immediately after switching on.

The C128 -BASIC has compared to the C64 BASIC additional commands for program control, sound and music production, far less cryptic commands to control the floppy drive and comfortable graphics and drawing functions for the 40 - character video chip - but not for the VDC. In conjunction with the imaginary for the C128 floppy disk drives in 1571 and 1581 and the loading and saving programs faster than on a C64.

As a second operating system CP / M-Plus (V3.0 ) was included with the C128. The C128 - CP / M was designed so that programs for the Kaypro computer, then the most widely used CP / M machines, were usually directly executable. The Commodore CP / M was very slow because the processor effectively only ran at 2 MHz ( instead of the usual in other CP / M machines 4-6 MHz) and because CP / M 3.0 and even more complex and slower than the more common CP / M 2.2.

In addition to the original operating system GEOS was offered for the C128 (now freeware ). Meanwhile, there are also a Unix derivative called Lunix for the C128 and one incomplete port of Contiki.

Furthermore, the C64 mode of the C128 allows it to use all operating systems, which are available for the C64. For instance, the BASIC V2 installed the C64 in the C128, and it can be, for example, the C64 version of GEOS and other operating systems such as Contiki use it without problems on the C128. To program a Pascal compiler could be installed as the C64, which was especially for training in schools is important.

Market success of the C128

After the change of the company founder Jack Tramiel and a large part of the development team to Atari Commodore of the C128 was hastily developed as a successor and upgraded model for the Commodore 64. With the CBM510 already existed a device that was much more modern in many ways, so it had a CPU with integrated bank switching and up to 1 MB address range. But in spite of great similarity (same video and sound hardware like the C64 ) was the CBM510 largely incompatible with the C64 and was only produced in very small numbers, in Europe, he was not even offered. In addition, he lacked the ability to represent 80 characters per line, which was seen as essential for professional use. It was therefore decided to develop a new system that should be largely binary compatible to the still successful C64 on the one hand, on the other hand - had additional useful skills for professional use - about advanced operation modes. It was expected the imminent end of the 8 -bit product line and hoped to be able to the delay with the C128 by one to two more years.

The C128 was far less successful than the C64. He should replace the C64, but offered for the target group no significant changes that would justify the significantly higher price. In addition, 1985 was in the professional use of computers, the change from CP / M to IBM PC - compatible hardware with MS -DOS operating system, as well as 16 - and 32 -bit processors (Intel 8086, Motorola 68000 ) already largely completed. Since games could hardly take advantage of the new features of the C128, he offered the normal home user who wanted to use mostly games, only small advantages over the C64. Thus, only about 4 million units were sold, compared with about 17 million C64.

The result was that a corresponding software failed to offer and most of C128 were in the C64 mode. In addition, the C128 came at a time on the market, as already leaked the first rumors about the Amiga.

Another reason for the lack of acceptance for the computer was the complex system architecture with three different operating modes, two processors and two graphics chips, bank switching, several different types of RAM to be used, and another processor in the floppy drive. One principle outdated basic structure was wrested by large cost of materials a while above average, but not outstanding performance.

Ultimately survived the C64 against all expectations further nine years and was only in 1994 set years after the C128 was taken off the market.

The various C128 models and variants

Commodore produced the C128 in several variants.

Besides the standard version Commodore also produced in different countries ( among others Germany, Italy, France) adapted models in which by means of the "caps" - or " Ascii / DIN " button between international and local mode can be switched. In local mode, is a set of characters with umlauts and other special characters of the language as well as an adapted keyboard occupancy. For omitted compared to the U.S. model of the slightly improved character set for the C128 mode is instead in the international models - the unchanged C64 character set in C128 mode used - as long as the local mode is not enabled.