The Second Processor consists of a 65C102 microprocessor system and 64K of Random Access Memory (RAM). In addition, it contains an interface between itself and the BBC Microcomputer called the Tube.

With a Second Processor fitted, the job of the BBC Microcomputer is to serve as an I/O Processor; that is, to handle all the inputs and outputs (keyboard, RS423, text and graphics output to monitors, printer output, disc drives, cassette recorders and so on).

The job of the Second Processor is to run languages such as BASIC, assembly language, word processing, and to run user programs. The Tube handles the two-way communication between the BBC Microcomputer and the Second Processor, and this leaves the Second Processor to get on with running programs, while the BBC Microcomputer looks after all the inputs and outputs as requested by the Second Processor.

The Second Processor offers you two major features: very fast program execution, and far more user memory.