Several "Second Processor" expansions were created by Acorn or other hardware companies for the BBC that allowed the BBC to use one more additional CPUs. Acorn had already set in place development standards that if followed, would allow all software to work with Second Processor expansions. Thus, most any software will run fine and may even run faster if Second Processor is used. Typically these expansions also included other hardware such as a disk drive, hard drive, modem, network interface, and memory matched to the CPU. These basically turned the BBC Micro in to a smart terminal for a more advanced computer system that was not bogged down with things like I/O and graphics calculations (which the BBC continued to handle using the internal CPU). A BBC smart terminal allowed the second processor to just crunch numbers. Or, everything could be offloaded to the second system letting the BBC have full access to 44K of memory (under normal conditions only 24K was usable, 28K if the screen RAM was usurped). This was automatic for any 6502 varient. Most Second Processor expansions were designed to run a different operating system such as CP/M, MS-DOS compatible, or UNIX. Acorn's own expansions were used to evaluate different CPUs both in-house and in real world use. They concluded that no CPUs were sufficiently better than the 6502 and set about designing their own CPU that would come to be known as Arm-1 (which was then used in a BBC 2nd CPU expansion). Despite all the business intentions of these expansions, there were games made to run in these co-processor environments.
6502 at 150%-750% clock rate. All games written to Acorn's development standards can benefit from it. No known games are specifically optimized. Do not tag cpu-6502 unless the game is specifically designed for a 2nd 6502.
65c102
65sc12
Z80 The CP/M expansion, or UNIX
6809
8088 A DOS-Compatible expansion, or UNIX
80186 Another DOS-Compatible expansion
32016 UNIX (did any other OS ever run on a 32016 ?) This was advertised as turning a BCC into a mainframe computer. Note that any 2nd CPU expansion that adds networking potentially makes the BBC into a decent webserver.
68000 UNIX
68010 UNIX
68020 UNIX
68030 UNIX
68030 UNIX
Arm-1