RISC OS: Installing ROOL Desktop Development Environment (DDE) tutorial

In this article we’ll have a look at how to install ROOL DDE correctly on different RISC OS releases to make sure it works to the best of its capabilities.


This, as all my other tutorials on ROOL DDE tools, is not an official guide. All the details provided here are the result of hacking and/or playing around with the tool. Given the lack of official documentation with such level of details (and so many comments on forums asking questions on the matter) I have decided to publish what I know. So please take the information presented here with a grain of salt as it may not be 100% accurate. I welcome any correction with comments (in the comments section below the article) or on the ROOL forum. 

Please note: ROOL DDE is different than the old Acorn DDE, SO PLEASE DO NOT USE the procedures explained here to install the old Acorn DDE on your RISC OS 3 for retro-coding, thanks!


ROOL DDE (stands for RISC OS Open Desktop Development Environment) is the modern evolution of the Acorn C/C++ suite (later improved and rebranded Acorn DDE). The original Acorn suite went through different “phases” with the installation process and so did also ROOL DDE. The early versions of Castle/ROOL DDE came with an installer application that made things very easy, however from DDE 24 (AFAIR) ROOL removed the installer. So far (up to release DDE 29) installation is still manual.

DDE has been the main development environment on RISC OS for decades and you still need it if you want to build RISC OS from sources. If you don’t have it yet you can purchase your copy from the ROOL official shop here.

If you are using RISC OS 5.xy, DDE is still simple to install on it, however, if you are using an older RISC OS release then you need to be a bit more careful when installing DDE.

Below you’ll find all the installation details I have found so far for all supported RISC OS releases.

Installing ROOL DDE on RISC OS 5.2y

Given that I have no knowledge of anyone still running RISC OS 5.0y or 5.1y I’ll go straight to 5.2y. 

At the moment of writing this tutorial RISC OS 5.2y is directly used to develop ROOL DDE, so there are no special requirements.

For older versions of ROOL DDE (for Castle DDE or before ROOL DDE 24):

  • Mount the CD ROM with your DDE release
  • Open it in the filer by clicking on the CDROM icon on RISC OS desktop icon bar
  • Run the !Install_CC application and follow the instructions there

For recent versions of DDE (from ROOL DDE 24 onwards) all you need to do when you receive your copy of ROOL DDE is:

  • Unzip the ROOL DDE archive
  • Select all the content in the archive
  • Copy all the selected content onto your boot disc partition (the partition where you have the !Boot and the directory called Apps).


When installed on your disc the last bit to do is to open the directory called AcornC/C++ and then the subdirectory called Developer and finally double click on the script called !SysMerge. Before you do that make sure your Boot$Dir variable is correctly set. To check that open a Task Window ([CTRL] + [F12]) and run the command:

show Boot$Dir

Make sure the output correspond to your boot disc and boot file, for example:

Boot$Dir : ADFS::HardDisc4.$.!Boot

When you are sure your Boot$Dir is set correctly then run the !SysMerge in the Developer directory and you’re done. This last action will install the DDE tools required modules in your !Boot.Resources.!System.

Updating ROOL DDE on RISC OS 5.2y

If you are updating your existing ROOL DDE usually all you have to do is copy the updates on top of your existing ROOL DDE directories (if the updates are part of the same major release, for example DDE 29b is an update of DDE 29a). My recommendation is to read the update instructions (when provided by ROOL) per each specific update. If no update instructions are provided and the update is not to a new major release then yes follow the method described at the beginning of this paragraph.

However, if your update is a new major release (so for example you have DDE 28 installed and you’ve just received DDE 29) my recommendation is to backup/move your old DDE somewhere. I personally use a dedicated directory I created in $.Programming, something like the following picture:


I usually move the old release in there in its appropriate container and install the new one clean. I do that to make sure I still have a working DDE before start testing the new one.

Installing ROOL DDE on RISC OS 4.xy

This is where things starts to get a little tricky. 

First of all, before you begin the installation process make sure your Boot directory is set correctly:

show Boot$Dir

and make sure the output is correct to where your !Boot app and Apps directory are on your boot partition.

If you have DDE from 24 onwards, before installing your ROOL DDE make sure you download a copy of the System Resources from:

System resources

Unzip it and and run the !SysMerge script you’ll find in there. 


When !SysMerge has completed then it’s time to install your ROOL DDE by following the procedure explained above in Installing ROOL DDE on RISC OS 5.2x. However, my recommendation is, before you do that, reboot your computer, this to make sure no older Modules are in use before you proceed with the installation steps.

If you have DDE from 24 onwards then, when you’ve installed your ROOL DDE there is one last thing left to do, patch your ROMs.

To patch your ROMs is very simple:

  • Open the directory called AcornC/C++
  • Then keeping your [SHIFT] key pressed double click on the icon called !SetPaths (this will open it as a directory instead of running it) and release the [SHIFT] key
  • Finally double click on the icon called !RomPatch

You are now ready to run your DDE and DDT and it should work to the best of its capabilities.

If you are using this system mostly for software development then I recommend to add !RomPatch to your list of applications automatically executed at every boot, like the following:


Then press Set and press Set again to complete.

This is vital to make DDT debugger to work fine on RISC OS 4.xy, and NO !SetPaths doesn’t run it for you, so you have to do the above steps otherwise your DDT may quit unexpectedly while you are debugging your code with an Unknown SWI error, so you have been warned! 🙂

Updating ROOL DDE on RISC OS 4.xy

This procedure should be used only when you’ve installed ROOL DDE on RISC OS 4.xy following the installation procedure above for 4.xy.

To update ROOL DDE when is a bug fixing release (aka NOT  a major release) you should just copy the content of the bugfix release on top of the same directory on your main disc partition.

When the update is a new major release (so for example you have DDE 28 installed and you want to update to DDE 29) then I recommend to move your old DDE in a backup and install the new DDE following the installation procedure above.

Installing ROOL DDE on RISC OS 3.xy

Before you proceed with the installation make sure you have installed on your HD/CF Card the Acorn UniBoot (Universal Boot) and you have configured your RISC OS computer to boot from HDD/CF card where you’ve placed the Universal Boot sequence.

If you do not have UniBoot installed on your Archie, you can download one from the riscos.com website here and if instead you fancy a richer UniBoot than the Acorn standard one then retro-kit website has one for you here.

To install ROOL DDE on RISC OS 3.5y, 3.6y and 3.7y you can use the procedure explained for RISC OS 4.xy straight away.

However, for RISC OS 3.0y, 3.1y, as well as 3.2y (I believe) be careful installing the new System Resources, I have noticed that some System Resources updates from ROOL could actually break RISC OS 3.1y boot (if this happens to you when installed the System Resources, then please make sure you report the issue on the ROOL forum).

Ok that’s it for now, thanks for reading and I hope you’ve found some useful information here. If you enjoyed this post, please don’t forget to support my blog by:

  • Visiting my on-line hacking and engineering merchandise shop on redbubble.com by clicking here
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And as always if you have any questions please feel free to use the comments section below.

Thank you! 🙂

What next?

  • Learn or refresh your knowledge on how to debug your software on RISC OS using DDE DDT here

If you are interested in coding on RISC OS:


One thought on “RISC OS: Installing ROOL Desktop Development Environment (DDE) tutorial

  1. Pingback: RISC OS: Using the Acorn / ROOL Desktop Debugging Tool DDT (part 1) | Paolo Fabio Zaino's Blog

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