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Programmer's Reference Manual


About this manual

Summary of contents

This manual gives you detailed information on the RISC OS operating system, so that you can write programs to run on Acorn computers that use it.

Part 1

Part 1 introduces you to the hardware used to run RISC OS, and to the fundamental concepts of how RISC OS works.

Parts 2 to 5

Parts 2 to 5 inclusive give you more detailed information on separate parts of RISC OS:

  • Part 2 describes the kernel (or central core) of RISC OS
  • Part 3 describes the filing systems
  • Part 4 describes the window manager
  • Part 5 describes the system extensions to RISC OS

We've laid out the information in these parts as consistently as possible, to help you find what you need. Each chapter covers a specific topic, and in general includes:

  • an Introduction, so you can tell if the chapter covers the topic you are looking for
  • an Overview, to give you a broad picture of the topic and help you to learn it for the first time
  • Technical Details, to use for reference once you have read the Overview
  • SWI calls, described in detail for reference
  • * Commands, described in detail for reference
  • Application notes, to help you write programs
  • Example programs, to illustrate the points made in the chapter, and on which you can base your own programs.

The Appendixes contain:

  • an introduction to writing assembler for the ARM chip, on which RISC OS runs
  • information of interest to RISC OS programmers writing compilers and other language-based tools
  • file formats used by current RISC OS applications.

The tables gather together information from the whole manual, giving lists that you will find useful for quick reference.


The separate volume of Indexes contains:

  • an index of * Commands
  • an index of OS_Byte calls
  • an index of OS_Word calls
  • a numeric index of SWI calls
  • an alphabetic index of SWI calls
  • an index by subject.

Conventions used

Certain conventions are used in this manual:

Hexadecimal numbers

Hexadecimal numbers are extensively used. They are always preceded by an ampersand. They are often followed by the decimal equivalent which is given inside brackets:

    &FFFF (65535)

This represents FFFF in hexadecimal, which is the same as 65535 in ordinary decimal numbers.


Courier type is used for the text of example programs and commands, and any extracts from the RISC OS source code. Since all characters are the same width in Courier, this makes it easier for you to tell where there should be spaces.

Bold Courier type is used in some examples to show input from the user. We only use it where we need to distinguish between user input and computer output.

Command syntax

Special symbols are used when defining the syntax for commands:

  • Italics indicate that you must substitute an actual value. For example, filename means that you must supply an actual filename.
  • Braces indicates that the item enclosed is optional. For example, [K] shows that you may omit the letter 'K'.
  • A bar indicates an option. For example, 0|1 means that you must supply the value 0 or 1.

Many of the examples in this manual are not complete programs. In general:

  • BBC BASIC examples omit any line numbering
  • BBC BASIC Assembler programs do not show the structure needed to perform the assembly
  • ARM Assembler programs assume that header files have been included that define the SWI names as manifests for the SWI numbers. See the chapter entitled An introduction to SWIs
  • C programs assume that similar headers are included; they also do not show the inclusion of other headers, or the calling of main().

Finding out more

For how to set up and maintain your computer, refer to the Welcome Guide supplied with your computer. The Welcome Guide also contains an introduction to the desktop which new users will find particularly helpful.

For details on the use of your computer and of its application suite, refer to the RISC OS User Guide and RISC OS Applications Guide supplied with it.

If you wish to write BASIC programs on your RISC OS computer you will find the BBC BASIC Reference Manual useful.

Your Acorn supplier has available the Acorn Desktop C and Acorn Desktop Assembler products, which you can use to write programs in (respectively) C and ARM assembler. Both products run in a desktop environment with full supporting tools. The manuals for both products are available separately if required: they are entitled Acorn ANSI C Release 4 and Acorn Assembler Release 2.

Reader comments

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This edition Copyright © 3QD Developments Ltd 2015
Last Edit: Tue,03 Nov 2015