Explaination Requested: Why are mobile OSs all firmware?

[Urzu1000]

This could be a potentially stupid question, but please hear me out!

I just bought an unlocked Android phone (ASUS Zenfone 2) last week, and it's my first smartphone. I've been doing a lot of research on them trying to develop a better understanding of how these things work. I've been using a dumb phone for the past 6 years.

One thing I've come to notice is that installing a different ROM (basically an OS) onto the phone has the potential to brick it. This seemed a little odd to me, until I realized that the OS is installed as firmware.

On a computer, the BIOS is the firmware for the MoBo, and you can install an operating system (or systems) separately from that. Regardless of what you install, be it Windows, Linux Mint, etc, the firmware doesn't change.

Why is this different in phones? Wouldn't it make more sense to have a BIOS screen?

 

[Solandri]

A BIOS is needed on a PC because you can install all sorts of generic equipment into it. Since the motherboard manufacturer doesn't know what brand of HDD or which CPU you'll be installing, they need a set of communications protocols which will work with all possible HDDs, CPUs, memory, etc. That's what the BIOS is - basic input/output system.

On an embedded device like a mobile phone, all this hardware is hand-picked by the designers. You can't put different hardware into it (aside from a memory card if your phone has a slot for it). So they don't need to put a BIOS in the phone - they can just program it to directly talk to the hardware.