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Heater. wrote: »
The SoC on the Raspberry Pi has a video processor (GPU) that is actually the first thing to run at power up. That video core only understands FAT and can boot from a FAT partition on SD card (Or elsewhere I think now a days).
For those using Raspbian OS on the Raspberry Pi the SD contains a small FAT partition and the rest is ext4 format. The video core reads the Linux kernel image from that FAT partition into memory and the fires up the ARM processor to run it. Linux of course uses the ext4 partition for it's root file system. As Tor says, no one need know any of this to get started, just write the Raspbian image to SD and away you go.
Then the there is the NOOBS thing. Which I have never used. In NOOBS the whole SD is initially FAT format. The user just copies NOOBS to there (file copy not image writing). On start up NOOBS runs and allows installation of the actual Linux, or other, operating system.