Installing a Sideways ROM Board in the BBC Model B

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The BBC Model B is one of my favourite retro computers. Even over 40 years after its release, there are still plenty of upgrades available that make using it even more enjoyable.

One of the most useful upgrades is a Sideways ROM board, which allows you to install several ROMs at once instead of being limited to the standard motherboard sockets.

In this post, I'll walk through installing one into my BBC Model B and show the finished result.

What is a Sideways ROM?


The BBC Model B stores much of its operating software in ROM (Read Only Memory) chips rather than loading everything from disk.

These ROMs can contain things like:

  • BBC BASIC
  • Disk filing systems
  • Utility software
  • Programming languages
  • Diagnostic software

As you begin expanding your BBC Micro, you soon run out of ROM sockets.

A Sideways ROM board solves this by providing additional ROM sockets, allowing multiple ROMs to remain installed at the same time.

Why Install One?

Although the BBC Model B is an incredibly capable machine, swapping ROM chips every time you want to use different software soon becomes inconvenient.

Installing a Sideways ROM board gives you:

  • More ROM sockets
  • Easy expansion for future ROMs
  • Less wear on the motherboard sockets
  • A cleaner and more flexible setup

If you're planning on using your BBC Micro regularly, it's one of the best upgrades you can make.

The Installation

The installation itself is fairly straightforward but, as with any vintage computer, it's worth taking your time.

Opening the BBC

The first step is removing the top cover and keyboard to gain access to the motherboard.

Since these computers are over forty years old, it's always worth checking that everything looks in good condition before installing any upgrades.

Remove ICs

Next remove IC73 and IC51, carefully so as not to bend or break the pins.
Recommended to use an IC puller.

Bend Power Connectors

The power connected next to IC73 are slightly too tall for the board to fit over, carefull bend the power clips at a 90 degree angle.

Remove Link S21

Remove the bottom S21 Link

Connect Power

Connect E1 (red lead) to the right hand side of link S21
Connect E0 (black lead) to the left hand side of link S21

Fitting the Board

The Sideways ROM board plugs directly into the BBC's motherboard.

The most important thing here is making sure every pin lines up correctly before pressing the board into place.

Take your time and double-check the alignment before applying any pressure.

Installing the ROMs

Finally refit IC73 and IC51 on to the sideways rom board, which are directly above the previous sockets.

Testing the Upgrade

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

After powering on the BBC Model B, the machine booted successfully and recognised the installed ROMs.

It's always satisfying when an upgrade works first time!

Final Thoughts

I'm really pleased with how this upgrade turned out.

The Sideways ROM board is a simple installation that makes the BBC Model B much easier to expand in the future. Even if you're only using the standard ROMs initially, having the extra capacity means the machine is ready for future upgrades as your collection grows.

If you're restoring or regularly using a BBC Model B, I'd definitely recommend considering one of these boards.

Watch the Full Video

If you'd like to see the complete installation, including fitting the board and testing the machine, you can watch the full video below.

What's Next?

This is just one step in my BBC Model B restoration and upgrade series. Upcoming projects include:

  • Burning and Adding ROMs to the sideways rom board
  • Sideways RAM board install
  • DISK Drive Repair

Thanks for reading, and if you enjoyed this article, be sure to check out my YouTube channel for more retro computing, electronics, and engineering projects.

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