Beta RPi ROM - nightly development build

I am puzzled as how one uses the R14 Beta RPi ROM. I see that it contains a file of type ROM (&FE5) called “riscos”.

I might have imagined that this was a replacement for RISCOS/IMG in the DOS partition, were it not for the fact that it counts out at 2,523,136 bytes, yet the current RISCOS/IMG (17-Feb-15) in the DOS partition is 5,242,880 bytes.

Can any one help me over this, please? What am I misunderstanding?

The 2.5MB ROM will be compressed the 5.2MB not.
rename the new download to whatever your old ROM is i.e. RISCOS/IMG

The nightly ROMs are compressed, while the RC beta ROMs aren’t. It’s just a harmless discrepancy between the two build methods.

Fuller explanation:

ROM compression is an extra step that’s performed after the ROM has been built. For the nightly builds this compression only happens when the zip file is being prepared. For the beta RC images the zip file creation step would have never been run, so they’re using a raw uncompressed ROM straight from the build system’s output dir.

Although there’s no technical reason for the Pi to require compressed ROMs, I think we initially enabled them for the nightly builds so that we wouldn’t have to worry about the ROM taking up too much space if we ever had to share the boot partition with a Linux kernel in a dual-boot setup.

Thanks to you both for the short and the fuller explanation.