VirtualAcorn Technical support:
Reading ADFS floppy discs on a Mac with no floppy disc drive

Modern Apple computers do not support internal floppy disc drives, so the only floppy drives that can be used with Mac OS X are external USB drives. These drives 'fool' the USB storage system into thinking that it's dealing with a (very slow) USB flash drive rather than a floppy disc. The actual reading/writing of the disc is performed by the firmware in the disc drive. This presents a problem for RISC OS users as the firmware in these drives can only understand discs with 512 bytes per sector. RISC OS format floppy discs use 1024 bytes per sector.

As such it's simply impossible to directly read an Acorn format floppy disc on Mac OS X. However all is not lost provided that you can find a Windows PC with an internal floppy disc drive. It's then possible to use the Omniflop disc reader to generate an ADF (Acorn Disc Format) image of the floppy disc concerned. This image can be copied to a USB flash drive and transferred to Mac OS X.

Note : Once you have read the floppy discs and produced the ADF image files make sure you keep a backup of these ADF files. Any floppy discs that still exists will be years past their MTBF (Mean Time Between Failures) and could fail the next time you need them. In addition floppy disc drives themselves are legacy devices and once they fail obtaining replacements could be difficult.

Once you have read all of the floppy discs and transferred all the ADF files to a USB flash drive the following instructions explain how you can read the ADF files in RISC OS:

  • Copy any .adf files you want to use into the VirtualRPC Harddisc4 folder:
    • Usually - Applications/VirtualAcorn/VirtualRPC-xxx/HardDisc4
  • Download a copy of ADFFS
  • Install ADFFS somewhere sensible, for example HostFS::Harddisc4.$.Filing.ADDFS.!ADDFS
  • Ensure that you change the filetype of any .adf files to &FCE
  • Run !ADDFS and then double click on an .adf file

Using this method all sorts of disc images can be read. RISC OS will believe that the contents of the .adf file is really in the ADFS::0 floppy disc drive. So even software (and games) that checks the contents of ADFS::0 can be run.

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 Copyright (c) 2015 3QD Developments Ltd. All rights reserved. All trademarks are acknowledged. All details are correct at the time of publication, E & OE.
Last Edit Date 14/01/2015