RPCEmu User Manual

RPCEmu is a emulator of Acorn's Risc PC and A7000 machines. It is a work in progress and should be considered of Alpha Quality.



Most PCs made since 2010 should be able to deliver performance similar to real Acorn hardware.

RPCEmu reports how many millions of instructions are executed per second (MIPS). This figure has been widely misinterpreted in the past, partly due to Acorn giving their machines very optimistic performance figures, and partly due to confusion with the DMIPS figure reported by the Dhrystone benchmark.

It is better to compare RPCEmu and real Acorn hardware running actual applications or benchmarks, instead of comparing RPCEmu's MIPS count with what an ARM6 or ARM7 is theoretically capable of.



Download the .zip file and install it to a location of your choice.

Linux and FreeBSD

The Linux and FreeBSD versions are provided as source code; as such it must be compiled before use. Please refer to the Linux compile instructions or FreeBSD compile instructions.

ROM Images

RPCEmu requires a RISC OS ROM image to work, please refer to these instructions for details on how to acquire them.

The Mouse

RISC OS uses a three-button mouse, if your host machine only has two buttons the right and left buttons are mapped correctly, with the middle 'menu' button accessible via the windows menu key (to the left of right ctrl key).

On Linux hosts pressing both left and right mouse buttons simultaneously will generate a middle button click (depending on X server configuration).

Two-button Mouse Mode is available from the Settings Menu; it swaps the right and middle mouse buttons, allowing the more common RISC OS use of Select and Menu on two-button mouse systems such as laptops.

The Menu

RPCEmu contains a menu to access most of the configurable aspects of the program.

menu on windows

Using floppy disc images

RPCEmu supports three different floppy disc image formats, ADF, ADL and IMG. A disc image is a file on the host machine that contains the contents of a floppy disc.

You can select which disc image to use on each drive by using the UI provided on the 'discs' menu.See above.

RPCEmu supports up to two high-density floppy disc drives, :0 and :1 with one configured by default :0.

If you wish to configure two drives in RISC OS, use the following command or use !Configure to add them.

*configure floppies 2

Using hard disc images

Up to two IDE hard disc files can be used (only one if a CD-ROM is used). They are called hd4.hdf and hd5.hdf in the program's working directory. Pre-formatted hard drive files are available from the website.

Once the hard disc image is in place you can copy the boot sequence from floppy, CD-ROM or HostFS. To get RISC OS to boot off hard disc, type the following commands at the command prompt:

*dir adfs::4.$
*opt 4,2
*configure filesystem adfs
*configure drive 4
*configure boot

It is possible (though not recommended) to prepare and format your own hard disc files. If you wish to try this, take note of the following:

Using HostFS

HostFS allows you to use a directory on your host operating system as a RISC OS drive. This allows you to more easily move files between the host OS and RISC OS than either Floppy disc imanges or Hard disc images provides.

HostFS always reads from the hostfs directory. Filetypes are represented as a 3-digit hex number after a comma, or a pair of load/exec addresses.

You can use HostFS as main bootable drive within RISC OS by issuing the following commands:

*configure filesystem hostfs
*configure boot

Using the CD-ROM

RPCEmu provides two methods of accessing CDs from RISC OS: ISO images and direct access to the host's CD-ROM drive.

You may need to configure RISC OS to have a CD-ROM drive. If you use a CD-ROM drive you may only have one HDF hard drive file. Use !Configure or use the following.

*configure cdromdrives 1

Use the settings menu described above to access CDs.


Networking is available on the Linux and Windows platforms, please see the RPCEmu Networking Guide for details.


RPCEmu does not support direct printing from RISC OS (there is no parallel port emulation or pass-through to the host parallel port). So the recommended method of printing is to install PrintPDF, print your documents to PDF files, copy them to your host operating system via HostFS and print them there.

Large screen modes

Warning: DO NOT DO THIS ON REAL HARDWARE it could damge it

RPCEmu can provide up to 8MB of video RAM (VRAM). This enables you to use higher resolutions and more colours than actual hardware.

You will need to do the following:

  1. Enable more VRAM.
  2. Alter the video bandwidth limits
  3. Optionally, use a better MDF (Monitor Definition File)

1. Enable more VRAM

On the Settings->Configure window, make sure a Risc PC hardware model is selected and that VRAM is set to 2 MB (8 MB if OS supported).

2. Alter the video bandwidth limits

You need to alter the amount of data that RISC OS is allowed to send to the Video chip. This is controlled by a setting in !Boot.

Edit the file in !Boot. This could be in one of several places depending on which version of RISC OS is in use.

Check the following files:

The file should have a line that looks something like this (with either 3, 4 or 5 number fields):

/<Obey$Dir>.BandLimit 38000 76000 152000 80000

Alter the numbers only, adding one zero to each number field:

/<Obey$Dir>.BandLimit 380000 760000 1520000 800000

Save the file and reboot RISC OS.

Note, do not be tempted to add more zeros as this will not work (this appears to overflow a calculation by RISC OS).

3. Optionally, use a better MDF (Monitor Definition File)

This MDF contains mode definitions for most historical RISC OS modes and new modes for most common LCD panel sizes that are in use today.

RPCEmu Generic MDF

Copy the MDF to the directory !Boot.Resources.Configure.Monitors then use the !Boot Screen settings to choose this monitor and desired default screen mode.

Finding Help and Reporting Bugs

If you have any questions or need help, there is a RPCEmu Mailing List, however please specify the version number to avoid confusion. Your patches, suggestions and even bug reports are gratefully recieved.

Contributions: Matthew Howkins, Peter Howkins, Sarah Walker.