BBC Micro expansion units: Wikis


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Teletext Adapter alongside a BBC Model B

BBC Micro expansion units, for the BBC Microcomputer were peripherals in a box with the same profile and styling as the main computer.


Second processors

The Second Processors 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.


6502 Second Processor

The 6502 Second Processor was clocked at 3 MHz, a full 50% faster than the 6502 inside a BBC Model B, and also had 64kB of RAM, of which typically 30–44kB was free for application data (compared to as little as 8½kB on an unexpanded Model B, or even less with the disc interface).

Z80 Second Processor

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 ran at 6MHz and had 64kB of RAM.

32016 Second Processor

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 6MHz. 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 1MB of RAM as standard.

The processor is also inside the Acorn Cambridge Workstation this time using 10MHz parts and 4MB of RAM, sold as part of the Acorn Business Computer line.

Universal Second Processor

The Universal Second Processor was an adapter for BBC Master internal co-processor boards. This allowed the BBC B and B+ to use the Turbo board (4MHz 65C102 with 64kB of RAM) and the Master 512 board (10MHz 80186 with 512kB of RAM), by fitting them into this expansion unit.

ARM Evaluation System

One of the first production RISC processors, [1] the ARM Evaluation System was part of the development programme leading to the Acorn Archimedes and its early Arthur operating system. It was not branded "BBC" but is physically contained within the family's "cheese wedge" case. The ARM 1 processor was clocked at 8MHz, and was fitted with 2MB or 4MB of RAM.

In 2007 a new ARM processor board using an ARM7TDMI processor was designed and sold, without an enclosure but able to fit within the original case. [2]


The adapters connected to the BBC Micro's 1MHz bus interface. Adapters could be daisy-chained, allowing more than one to be fitted.

Teletext Adapter

The teletext Mode 7 inside the 8-bit BBC Micros made a teletext adapter an obvious expansion, and the BBC would broadcast telesoftware free over Ceefax.

Prestel Adapter

Similar in shape (Cheese Wedge) to the teletext adapter, the Prestel adapter enabled the user to connect to viewdata services over the telephone line.

IEEE 488 Interface

Allowed the BBC Micro to talk over an IEEE 488 bus to specialised equipment. "Acorn" rather than "BBC" branded.

Econet Bridge

Used to connect two Econet segments together. An Econet Bridge is capable of automatically learning a simple network topology and selectively forwarding packets from one LAN segment to the other using a simple routing table based on the contents of the network byte in the Econet packet.

The Econet Bridge is unique among the cheese wedge expansions, in that it is a stand-alone device that does not require a BBC computer to operate.


  1. ^ ARM Processor types
  2. ^ [1]

External links



Acorn Cambridge Workstation

ARM Evaluation System


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