RISC OS is an operating system that's unfamiliar to many people, so here comes a bluffer's guide...
What is RISC OS?
RISC OS is a new and different OS for the Pi. It isn't Linux, it isn't Unix, it isn't based on any other OS. It's the first ARM OS, begun in 1987 by the team who designed the original ARM processor. It's also a descendant of the OS used on the early 1980s BBC Micro... those who remember the BBC Micro might find some of its commands familiar. BBC BASIC is only a few keypresses away.
What's interesting about RISC OS?
It's small. It's fast. RISC OS is a full desktop OS, where the core system including windowing system and a few apps fits inside 6MB. It was developed at a time when the fastest desktop computer was an 8MHz ARM2 with 512KB of RAM. That means it's fast and responsive on modern hardware. The memory taken by apps is usually counted in the kilobytes. A 700MHz 256MB Raspberry Pi is luxury - what to do with all that memory?
RISC OS is also a lot simpler than modern OSes such as Linux. The pace of development has been a little slower than other OSes, which means there are fewer layers getting between you and the system. It's much easier to get stuck in and change things. It's also easier to understand. As a formerly closed-source OS, most of the interfaces are documented in a series of books called the Programmers' Reference Manuals (PRMs) which are included on the RISC OS Pi distro. That means you can change a lot of things without having to work on the OS code itself (which is available if you want it). It's very modular, so you can mix and match components, and the communications between modules are carefully documented.
RISC OS gets out of the way. It's a 'co-operatively multi-tasked' OS. While that means one misbehaving application can stall the system until you kill it, it also means you easily write apps that take over the whole machine - for example controlling hardware where you need predictable timing. RISC OS is a single-user OS, which means there's very little security - not great for internet banking, but very handy when you want to dig around and program the internals of the OS.
As a full desktop OS, there's also plenty of traditional desktop software available like drawing programs and desktop publishers. Features you've come to expect on a desktop like scalable fonts and printing are supported. RISC OS was big in UK education in the 1990s, and there's a large back catalogue of educational software.
OK, so what do I need?
RISC OS makes heavy use of a three-button mouse. If your mouse doesn't have three buttons, never fear - if it has a scrollwheel, pressing the wheel down counts as the middle button. The middle button is called 'Menu', for bringing up menus (which are context-sensitive everywhere - there are no menu bars). The other buttons are Select (left) and Adjust (right) - Select is the main button, Adjust often does something similar but different to Select.
After that, you're good to go. Note that RISC OS has no USB wifi support, so if you want to use wifi try an ethernet-wifi adaptor.
How do I get started?
Download and write an SD card for your Pi from the Raspbery Pi downloads section in the usual way. Once you've booted RISC OS, you'll find a file called 'welcome/html' on the desktop - double click this for a tutorial. The distro is supplied without ethernet enabled to speed the boot of Pis without network connections - the tutorial explains how to turn it on.
You can also find links to more tutorials on the RISC OS Open website
, including one written by RPi forum member 'Burngate'.
What's different from other OSes?
Apart from the mouse differences described above, RISC OS has several unusual ways of doing things. Apps are just directories whose name begins with ! (called 'pling'). They can live anywhere on any disc - every system can be different. They're launched by finding the folder on disc and double clicking them. RISC OS is centred around the Filer, the display of folders on your disc.
Along the bottom of the screen is the iconbar. Unlike other systems, these icons depict running apps. If you double click an app, all that will happen is it puts an icon on the iconbar, ready for you to do something (create a new document, start a new game, etc). A Select or Menu click on the icon is a good way to explore what these icons do.
RISC OS also makes heavy use of drag-and-drop... to save a document, drag a 'save as' icon from your editor to a folder on the disc - or drag the 'save as' box from one app to another to work on the edited document in a new program. You rarely need to make temporary files to save intermediate work.
There are many other design differences you can discover as you explore further into RISC OS.
I want to write a program!
Easy. Press Ctrl-F12 (opens a command window). Type BASIC and press return. You're now in BBC BASIC, ready to go. Type:
10 WHILE TRUE
20 PRINT "Hello world!"
Press Escape to stop the program (you might get bored after a while)
You can even write multitasking windowing programs in BBC BASIC. (Using a proper editor, I suggest
How do I get more software?
There are two package managers on the distro, called PackMan and !Store: PackMan will install and upgrade programs for you, while !Store allows you to organise the install yourself (and offers commercial software too). You can also install software manually - installing many RISC OS programs is as simple as copying files from a zip to your SD card (in RISC OS, don't unzip on other platforms).
Be aware that some old software won't run on the Pi, because ARM chips have changed in various ways between ARM version 2 (the original 1987 chip) and ARM version 6 (the Pi). Everything in !Store and PackMan should be fine, but that old floppy disc you found in the back of the cupboard...
There's a program called 'Aemulor' which will enable running older software - the developer is rumoured to be working on a Pi version. There's a list of tested ARMv6 safe software
, which also gives links on how to convert old software.
Help, I'm stuck!
As well as this forum, there's the official Community Support board on the RISC OS Open Forum
. Do drop by and ask for help if you need it.