Sorting out information from (old?) desinformation gathered from the internet...

[monoid]

I do not say it is possible to have RB on memory card. It depends where code for memory card access resides (bootloader or RB). It is probably bootloader, but theoreticaly a part of code could be in RB. You have to look in source code or developers might tell you. I am just a user...

If you make a mistake in RB code, you may repair it just by connecting it to PC via USB. But OK, you will not wear off the memory by experiments. But if you make a mistake in bootloader, you have a problém... I do not know, how easy it is to unbrick the player... And what is needed. You might need some kind of special hardware....

[bluebrother]

If I am not wrong iRiver H1xx allows in RB to run one of two instances of RB. One from flash (where bootloader and firmware is) and one from flash memory where song files are. User could somehow select desired version of RB during boot.

Yes, with the latest v7pre4 bootloader. However, there's an important pitfall: Rockbox will load its codecs (and plugins, themes etc.) from /.rockbox. It will do so in both cases. So while you could have a different version flashed than the one on disk this only works as long as those two versions are rather close together -- the moment the codec (or plugin) API changes you won't be able to use it anymore (read: it won't play any music, you'll just see errors).

So, there is sort of precedens of two different locations for RB. So, I guess one could be also on memory card. I am not telling, it would be easy to implement (I have no idea) nor it is sensible idea...

No. The only thing the h100 bootloader does is loading the main binary from flash. But there's (a lot!) more to that -- loading the main binary is only for speed reasons.

[monoid]

Thanks for pointing out the codecs thing. I did not know that. And also did not know that it was only in 7pre4 and so it was not in official release of RB.

I mainly wanted to say, that there were successfull efforts to load RB from other location than player's internal memory.

[saratoga]

You can hack up the bootloaders to load the binary from any path you can access from the bootloader, so assuming the bootloader has SD card access you're free to do that.

However on the AMS devices, the bootloader itself has USB access, so the only real risk involves flashing the bootloader itself.  Hence trying to hack it may do more harm then good.