[General Topics] plus_rlus:
I'm having trouble understanding the architecture of mobile (and Android) devices. I compare it a lot to the design of PCs, laptops, etc, which I know quite well.

Here's my understanding on how PCs work when booting:

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The hardware has firmware stored in ROM (Read Only Memory). Actually, Flash memory is used nowadays, on which the stored content can of course be changed, unlike real ROM memories in the old days. Because the firmware is hardware-specific and its operation is very critical, its content is rarely updated or otherwise changed. Installing new firmware is called flashing. Firmware in a PC is most commonly BIOS or UEFI, the task of which is (briefly) to first run the POST tests, provide some interfaces and finally start the software in the mass storage. By mass storage, I mean memory separate from the firmware's Flash memory, which can also be Flash memory, such as an SSD disk, or a more traditional hard disk.​

The BIOS (i.e. firmware) in the specified order (which first is the internal NVMe SSD or the external USB hard disk?) tries to load the software into the RAM memory for execution from mass storage MBR (Master Boot Record) part . Master boot record is a physical defined area in mass storage. Bootloader software is stored on this MBR part.​

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When the bootloader (located on the MBR part) is loaded into RAM and run, it knows the contents of the end of the disk and starts the kernel from there.​

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The kernel starts (in Linux) the init process, nowadays often Systemd, which starts the rest of the software.​

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What kind of memories and storages are most commonly found in Android devices? One main memory (i.e. RAM)? One Flash memory for firmware (i.e ROM)? Another separate flash drive that acts as mass storage? Possibly SD card and USB stick as external mass storage?

What is firmware on Android devices?

What is the bootloader in (located in MBR part) on Android?

Linux is the kernel used by Android, which is started by the bootloader? After that, Android continues to boot, how?

A pile of terms, which I have ambiguities:

Bootloader; What's it like on Android? It is often characterized as hardware specific. So is it the case that the bootloader in Android is firmware? So in Android, the firmware runs the tasks of the PC world BIOS and bootloader (located in the MBR part), and then starts the Android located on the mass storage?

Recovery; What is this technically?

Android ROM; I can't understand this. As far as I know, Android is an operating system located mass storage, not Read-Only-Memory firmware.

Rooting; On a PC, we are used to the fact that the owner of the device has root rights. Is it just that the manufacturers have decided to set the default root password to some generated random string, and by default, the user only has access to the basic user account?

After the above has been answered, I would like someone to explain to me (separately) technically, starting from the hardware level (where and how), how do Android devices booting and work? Links to additional information are also welcome. hank you very much! If anyone can answer my questions, thank you very much!