BBC Micro expansion units

A BBC Micro expansion unit, for the BBC Micro is one of a number of peripherals in a box with the same profile and styling as the main computer.

The second processors are connected to Acorn's proprietary and trademarked Tube interface. Only one second processor could be connected at a time. The terminology of second processor was slightly misleading, since connected and switched on, the system worked on a "master-slave" model, with the processor in the external unit taking control while the 6502 in the "main" computer simply took on responsibility for I/O.

The 6502 Second Processor (using a 65C02) was clocked at 3 MHz, a full 50% faster than the 6502 inside a BBC Model B, and also had 64 KB of RAM, of which typically 30–44 KB was free for application data (compared to as little as 8½ KB on an unexpanded Model B in graphics mode, or even less with the disc interface). A version of BBC BASIC II, called Hi-BASIC, was produced on ROM for this processor, and Hi versions of View, WordWise and Intersheet were also produced.

Various CAD programs were able to take advantage of the 65C02 Second Processor, as was the second processor-specific version of Elite.

The Z80 Second Processor required the floppy disc upgrade: it was aimed at business and enabled the BBC system to run CP/M programs. It came with a suite of software that included the COBOL programming language. It ran at 6 MHz and had 64 KB of RAM.

A sophisticated second processor sometimes branded as "Acorn Cambridge Co-Processor" with an Acorn logo, and sometimes as "BBC Microcomputer System 32016 Second Processor" along with the BBC Micro's owl logo. The device uses the National Semiconductor 32016 CPU and National Semiconductor 32081 FPU running at 6 MHz. It runs the non-graphical Panos operating system. Various programming languages are available including C, FORTRAN, Lisp, and Pascal, in addition to a version of BBC BASIC. The processor comes with 1 MB of RAM as standard.

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