Multi-boot

The Pi 400 will not start up with an empty SD card slot.

Mine’s never had an SD card in it and it boots up fine.

My Pi 400 gives the screen here when asked to start up with the SD card empty:

Your boot order has been changed from the default.

See here for details.

Many thanks for the link – this has explained it.

It has not been changed from the default. The only option was 1 (SD card) until after 3 Sep 2020 so I need to update my EEPROM.

In any case it’s a Pi 4 not a 400 — the latter didn’t exist until well after September!

It is a Pi 400. Its firmware is Sep 3. Talking of chicken and egg, then the firmware supplied with a hardware project must exist before the hardware did.

In any case it’s a Pi 4 not a 400

The ‘no SD card screen’ from the RPi400, perhaps not entirely accurately, does report itself as a Raspberry Pi 4.

I have a RPi 2 (old version) with a 120Gb kingston SSD attached. I first installed the standard 5.28 image on the SD card, after moved everything but the Loader part onto the SSD (FileCore reformatted) and the system booted fine. I then installed NOOBS on SD card and (re)installed RISC OS and Raspberry OS, altering the RO part for using SSD-installed !Boot. All fine. But Raspberry OS remained on the SD card portion, without using the SSD.
My question is, is it possible to dual-boot RO / Raspberry OS from SD card (RPi 2 can’t boot from SSD), but partitioning the SSD so both systems boot from SD but every other file is on SSD?
Sorry if sounds confusing, but can’t find a better way of explaining it. I already tried to clone the SD card onto the SSD, but it’s not possible to resize the RO partition (filesystem unknown),and formatting the part of SD I allocated for RO with HForm destroys the partition table.