Testing on Hardware Question

[MarkCR63]

Great tutorial and thank you.

I do have a question about testing on hardware. I have seen a few other "build from scratch" lessons like this and they all do the same thing when it comes to testing on actual hardware. The RP must have a Raspian OS already installed on the SD card and then the kernel.img file created in the tutorial overwrites a file on the SD Card. I come away feeling like we have not really created an OS from scratch. There are clearly other instruction files being loaded and executed before ours.

Is it not possible to create an SD Card that contains a tiny OS of our creation and is placed onto an SD Card with absolutely nothing else? My understanding is that the RP3/4 main processor, upon reset, looks to the SD card for the very first instructions that it must execute. Clearly, the instructions must appear at a very specific and fixed location on the SD card because the RP3/4 processor is not going to look for them in any other place. It may require some kind of very low-level formatting of the SD card. Nevertheless, why is this not possible? Thank you, Mark