For most models of Raspberry Pi, you can use the “RISC OS Pi” SD card image available on the Downloads page.
If you have a Pi 3 model A+, use NOOBS Lite to download the software.
Strictly speaking, there is no preparation necessary, as the format information is contained in the image file. Any SD card of 2GB or greater capacity should be OK, however, it may be worth checking the known good cards list as there have been problems with some cards. Incidentally, it has been reported recently that many cards sold as Sandisk are counterfeit, so if in doubt, buy from a reputable supplier.
Start with a blank formatted SD or SDHC card.
SystemDisc is part of the DiscTools suite, and is a general-purpose tool for managing the system software on modern RISC OS systems. SystemDisc allows you, easily and quickly, to initialise new SD cards for booting your RISC OS system, entirely from within RISC OS. It creates a two-partition SD card which can use all of the available space on your SD card.
Now you need to copy the ‘firmware’ files into !Boot.Loader where they can be seen by the Pi as it starts up (before RISC OS is started).
Now download the HardDisc4 image and copy that onto the filecore partition. You will now have a ‘cut down’ version of the recommended Raspberry Pi image without all the extra software bundled with the “RISC OS Pi” distribution.
Comprehensive instructions can be found here – there is little sense in recreating these directions here as they are not RISC OS specific.
Insert the SD card into the Raspberry Pi, and connect the other peripherals necessary. Power up the Pi, and you should see the RISC OS logo during the boot process, before being taken to the desktop. It is likely that the screen resolution will need changing to suit your needs, so please see the Beginners FAQ:Look and Feel
If the initial boot (or subsequent boot) fails, the first likely candidate is the SD card. Check it is seated correctly, check that the contacts in the card slot aren’t damaged in any way, clean it all up, and try again. If this fails, it may be that the SD card has become corrupt, and needs re-imaging. This is a good time to remind all users of the importance of backups…
The basic approach is the same – create an SD card with the firmware and the RISC OS boot drive – but there is not yet a pre-built SD card image available so the manual option is the only one.