C=128
The Commodore 128 was released in 1985. The long awaited heir to the Commodore 64 failed to raise the same interest as its predecessor, but it was a brilliant machine anyway, solving all of the 64's problems: more memory, new version of BASIC (7.0) with commands to handle graphics and sound (no more POKEing) and built-in 80-column support. The machine operates in one of three modes, selected at boot time:
Commodore 64 mode: in this mode, the computer is, for all intents and purposes, a 64. Old BASIC, old hardware. Complete compatibility.
Commodore 128 mode: this is the 128's native mode, with its new features and extra memory enabled.
CP/M mode: here, the Z80 wakes up and the user may run CP/M applications (provided there's a floppy drive installed).
Commodore (and two other suppliers) also had a 512 kbyte memory expander. The memory was not directly accessible by the processor (for program execution), but it could copy blocks of memory to/from the memory unit at 1 Mbyte/sec (using DMA). It is a little different from regular memory, but it is fast enough to store active data or program segments in. There are hacked versions and one commercial version of this memory expander that have 2Mbytes of RAM in them.
