Tube (BBC Micro)

Under the Tube architecture, the coprocessor runs the application software for the user, whilst the Micro (acting as a host) provides all I/O functions, such as screen display, keyboard and storage devices management.

A coprocessor unit can be coldplugged into any BBC Micro with a disk interface (whose ROM contained the necessary host software) and used immediately.

The other active components needed are a microprocessor, some RAM, a small ROM containing processor specific client code, glue logic such as an address decoder and a power supply.

The protocol for the use of these buffers was rigorously specified by Acorn Computers[1] and amounted to interprocess communication by message passing.

Only these 3 address lines are connected to internal Tube sockets, as found in the BBC Master or Universal Second Processor Unit.

Before shipping Tube add-ons, Acorn had strongly discouraged BBC Micro programmers from directly accessing system memory and hardware, favouring official API calls.