Installing a Sideways RAM Board in the BBC Model B

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The BBC Model B is one of the most expandable home computers ever made, with a wide range of hardware upgrades still available today.

In this project, I'll be installing a Sideways RAM board into my second BBC Model B and using its built-in diagnostic commands to verify that the installation has been successful.


Installing the Board

Before fitting any upgrade, I always take the opportunity to inspect the inside of the machine.

My usual checklist includes:

  • Dust buildup
  • Loose ICs
  • Corrosion
  • Leaking capacitors
  • Damaged PCB tracks
  • Previous repair work

Fortunately, this BBC Model B was still in excellent condition.

Installing the Sideways RAM board is fairly straightforward.

Unlike a traditional Sideways ROM board, this upgrade plugs directly into the 6502 CPU socket, with the processor then fitting into the socket on top of the board. Several flying leads are connected to the motherboard to provide the additional control signals required by the board.

Although the installation isn't difficult, it's worth taking your time.

  • Double-check the orientation of both the board and CPU.
  • Verify each flying lead before soldering.
  • Keep the wiring neat to avoid trapping them when refitting the keyboard.

Once everything was back together, the modification was almost invisible from the outside.

First add the ROM IC as shown in the photo below.

Install ROM

Next remove the 6502 CPU as shown below

REMOVE CPU
Next add the sideways RAM Board, it fits in the CPU socket, make sure Pin 1 is located correctly as shown below.
ADD RAM BOARD

Finally put the 6502 CPU into the socket on the RAM board, shown by the red square.
RE-INSTALL THE CPU

This is the installation of the board now completed.

Testing the Hardware

With everything reassembled, it was finally time for the moment of truth.

Powering on produced the familiar BBC BASIC prompt.

No smoke.

No burning smell and the correct prompt on boot.

Boot

Always a good sign!

The first thing I checked was that the BBC was still recognising all of the installed ROMs and expansions.

Typing:

*HELP

displayed the installed ROMs, confirming that Turbo MMFS, DFS and the other installed ROMs were still present and functioning correctly after fitting the Sideways RAM board.

Help Command

The board also includes its own built-in diagnostic command, making it easy to confirm that everything has been installed correctly.

Running:

*RAMSTATUS

displays the current status of the Sideways RAM board, allowing you to verify that it has been detected correctly and is operating as expected.

Check RAM Status

Having a built-in diagnostic like this is a really useful feature, as it provides immediate confirmation that the hardware is working without requiring any additional software or test programs.

YouTube Video

You can watch the full video of the installation on my YouTube channel or with the video below.

Final Thoughts

Installing the Sideways RAM board is a simple upgrade that adds another useful capability to the BBC Model B.

Although I haven't explored everything it can do just yet, having writable ROM space opens up plenty of possibilities for experimenting with ROM software and making the most of hardware such as Turbo MMFS.

The built-in *RAMSTATUS command also makes it quick and easy to verify that everything is working correctly, which is especially reassuring after completing the installation.

In future articles, I'll be taking a closer look at what can actually be done with Sideways RAM, including how software can make use of it and some practical examples of where it becomes genuinely useful.

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