Acorn
Cheese
Wedges
Acorn
Cheese
Wedges
The expansion units produced for the BBC Model B by Acorn have come to be known affectionately by Beeb enthusiasts as "cheese wedges" because of their colour and shape. They were intended to be half the width of the BBC Model B and with the same cross-section as the computer.
The first adapters came out in the spring of 1984. Curiously, the 6502 and Z80 second processors are referred to as early as 1982 in the BBC User Guide and the front cover to various Level 2 Econet books published in 1983 clearly shows the file server with a cheese wedge attached!
Below is what I hope to be an exhaustive list of the Acorn cheese wedges with a brief description of each:
6502 Second Processor
The original and, in my opinion, the best of all cheese wedges. At £199 when it came out in April 1984, the 6502 Second Processor cost half a new Beeb which is why it was not as popular as Acorn might have hoped. But those who could afford one could not fail to be amazed by what the little box could do.
Inside the cheese wedge is a 3MHz 6502C processor with 64K on board of RAM. The adapter connects via a 40-way ribbon cable to the Tube connector on the BBC. When the Tube is running, the current language is copied into the Second Processor's RAM leaving the rest of the memory available for user programmes.
By the addition of a 6502 Second Processor, all the limitations caused by filing systems and screen modes eating up the user RAM are completely eliminated - almost 32K of memory is available in any mode with any filing systems using the 6502 Tube. Running the special second processor version of BASIC, Hi-BASIC, frees up nearly 48K of RAM!!!
One of my 6502 Second Processors is pictured above, in the bottom left-hand corner.
Z80 Second Processor
I don't like the Z80 system and have spent most of the time since I bought my Z80 cheese wedge wondering why on earth anybody would want to turn their Beeb into a PC.
Nonetheless, the Z80 demonstrates the power of the Tube system on the BBC micro - not only could an extra processor the same as the Beeb's own CPU be added, but a totally different processor system could be connected up to change the whole nature of the computer.
The Z80 runs off discs in CP/N format, but as this is 10 sectors of 256 bytes per track, I can't see any advantage over using Acorn DFS.
My Z80 Second Processor is in the bottom right-hand corner of the picture above.
32016 Second Processor
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This one is the stuff of legend. It is also known as the Cambridge Co-processor and the Acorn Scientific. It was boxed as the Cambridge Co-processor as the pictures above show.
The 32016 was a new type of processor which was a part 16-bit and part 32-bit processor. This was one of the most powerful of all the second processors issued. I think it had on-board RAM of 1 megabyte but I don't know anything about the operating system it used.
My thanks are due to Matthew Cook for the photographs of the Cambridge Co-processor.
80186 Second Processor
Before the days of Pentium, people used to speak of 386 or 486 PCs. The 80186 Second Processor predates all this by some years by turning your Beeb into a 186 PC!
Again, you might legitimately ask why you would want to turn your lovely Beeb into a rotten PC but at least this cheese wedge came with 512K of RAM, 16 times that inside the Beeb! If it is anything like the Master 512 version, then the 80186 can be useful for reading 720K DOS discs and bridging that ever-widening gap between BBCs and PCs.
Teletext Adapter
Not all cheese wedges were second processors. The Acorn Teletext Adapter contained a teletext decoder and a bit of RAM to enable the Beeb to receive broadcast pages of teletext and, in its 1980s heyday, download programmes as part of the Telesoftware System. This is now sadly defunct.
The Teletext Adapter is my second favourite cheese wedge after the 6502. It connects to the 1MHz bus and is controlled by the Teletext Filing System ROM. Unfortunately this bumps up PAGE by quite a lot, even on the Master, so it is handy to have a 6502 cheese wedge attached as well.
I have a Teletext Adapter permanently connected to Station 1 enabling me to despair at the news and panic at how much share prices have fallen all at the touch of the BBC keyboard.
I now have a spare Teletext adapter and this is shown in the top right-hand corner of the picture above. It came without a plug so I haven't even tested it yet.
Prestel Adapter
The Acorn Prestel Adapter was an early form of modem which connected to a telephone line and the RS423 port of the BBC micro. When connected, you could use terminal emulation software such as that contained in the Prestel ROM to use Prestel, Viewdata, bulletin boards and all those kinds of things which went on in the 1980s. It was a sort of inter-net of the day, but no doubt more reliable and less expensive than the modern-day equivalent.
One of my Prestel Adapters, as yet untested, is shown top-left in the picture above.
Econet Bridge
It was not until recently that I discovered that the Acorn Econet Bridge was a cheese wedge. It has the distinction of being the only standalone cheese wedge, not needing to be plugged into a Beeb.
An Econet Bridge, put simply, is a communications unit between two Econet networks. There are limits on the size of Econets and when those parameters are exhausted, networks can be linked together to continue sharing fileservers by the use of one or more bridges.
The Acorn Econet Bridge is a miniature Beeb in itself containing a 6502-based system running the bridge software. It has a bit of RAM as a buffer to remember things and contains an Econet interface for each network. It has two Econet sockets to enable the bridge to be connected across the two networks. Each network is assigned a network number in the range of 1 to 127 to allow each station to retain a unique station number when taking the network number into account.
I think these things are quite rare. I have never seen one on E-Bay so I was lucky to get my hands on the one I have here.
ARM Evaluation System
This is rarest thing in the entire universe and would fetch at least a trillion guineas if one ever came up for sale on E-Bay.
It is nothing less than a whole Archimedes with 4MB RAM crammed into a cheese wedge with a Tube cable so you can plug it into your Beeb!!
IEEE488 Adapter
Exactly what an IEEE488 device is I cannot say but it sounds important and Beebs can communicate with them when an IEEE488 adapter is attached to the 1MHz bus.
As far as I know, this adapter is the only one to have cheese-wedge and non-cheese-wedge varieties. The metal box type is the later variety and I am lucky enough to have one of each.
A most perplexing thing as I have never heard of anybody making use of one.
E-mail me if I have missed any from the list!
Click here to see all my Cheese Wedges