of BIOS and OS

[pawlu]

What is the equivalent of the BIOS in open source systems like Linus/Android Distro etc etc ?

Is the bios in Raspberry pi 2 built in, or part of the installation image of say NOOBS ?

Can I have different OS in different SD cards opened in Raspberrypi ? In other words, change an external SD card and change to Android, Win 10 etc etc ?

[DougieLawson]

The Raspberry Pi doesn't have a BIOS.

There's some GPU firmware on your SDCard that gets the GPU running. The GPU starts the ARM processor and gets the Linux kernel running. There are hundreds of documents on the internet with details of how that process works.

Android is a NON-STARTER on the Raspberry.
Windows 10 IoT is not the Windows you know (and hate) on your Laptop. It's a specialised internet of things Windows system that only runs on an RPI2.

[ghans]

The Raspberry Pi has "firmware" instead of a BIOS. To confuse matters more , this firmware must reside on the SD card on all B models.

You will not even get error messages without a working SD card or when you forget to put the firmware on the card. The Pi will do nothing.

Using different SD cards is the easiest way for dualbooting a Pi in my opinion. The SD card works like a Desktop/Laptop harddisk - changing it of course alllows you to
use different OS. Just like a Gameboy cartridge.

ghans

[pawlu]

thanks for your prompt reply.

So, in plain language, I assume, that if I swap the SD card for another one, with, say OSMC image. my Raspberrypi2 will boot? Am I assuming that opensource OS have buit in startup, instead of the windows BIOS ?

[ghans]

Yes , any SD card will boot as long it contains both the firmware and an Operating System.

Of course don't forget that not all OS are compatible with all Pis , and not all firmware is compatible with all Pis.

To fix that , in most cases you have to update both firmware and the OS itself.

A recent version of OSMC should work on a Pi2 without problems.


ghans

[pawlu]

am I correct in saying that for any OS on asn SD card, in order to boot, it must have the Raspberry PI firmware. Which means that I will have to check if the particular OS, in my case , a Kodi OS, is compatable with Raspberrypi.

I am also experimenting with the Orangepi Plus, which, with all due respect, has more hardware features, (not necessarily better in performance)

I have discovered that the Oranepi plus does not play HD on Kodi .

[ghans]

Yes , the firmware is mandatory. The Pi does pretty much nothing without it.

ghans

[pawlu]

Does this firmware, alternative to BIOS, applies to all other open source hard ware , not just Raspberry pi ?

[DougieLawson]

Does this firmware, alternative to BIOS, applies to all other open source hard ware , not just Raspberry pi ?

It's specific to the BCM2708 & BCM2709 SoC chips used on the A/B/B+/A, CM, 2B & 0. It's closed source that's proprietary to Broadcom and as far as we need to know it does the following:

1. looks for the first primary FAT/FAT32 partition on the SDCard
2. Reads config.txt from there (if it exists)
3. Starts the GPU with the parameters from config.txt
4. Loads kernel.img or kernel7.img (unless there's an override in config.txt)
5. Starts the ARM processor running the kernel, passing the contents of cmdline.txt as a kernel parameter plus a few extra parameters that are generated from the GPU. (cat /proc/cmdline to see those.)

That kernel can be Linux, RiscOS, Win10IoT, BSD or something you've written for bare metal or anything else that can run on a single core ARM6 (A/B/B+/A+, CM or 0) or on a four core ARM7 (2B).

Everything is loaded from the SDCard. All the dumb chip can do for its bootstrap loader is read firmware from a FAT formatted partition #1 on /dev/mmcblk0.

[ghans]

All computers need binary firmware to boot. The binary firmware is always extremely specific
to the computer and cannot used on other computer models by simple copying.

So every board has its own binary firmware - which may or may not be open-source (The Pi firmware is definetly closed-source).

ghans

[pawlu]

Thanks a lot ghans.
Altough I am very familiar with microsoft OS, I am completely new to opensource, Linux, distros etc etc. and can only compare to microsoft structures.

[DougieLawson]

Thanks a lot ghans.
Altough I am very familiar with microsoft OS, I am completely new to opensource, Linux, distros etc etc. and can only compare to microsoft structures.

It's nothing to do with the OS that you're booting, it's all about the hardware you're booting it on and the low level boot loader.

Linux on and old X86 boots in exactly the same way that Windows does (it get a bit more complex when you move from BIOS to UEFI on an X86_64). The difference comes after the BIOS/UEFI stuff is done. Microsoft has a two stage boot loader that runs from the BIOS/UEFI. Linux has GRUB to do that.

[ghans]

Yes , even Windows 10 "IoT Core" has to use the firmware. Firmware is not software-specific but hardware-specific. All OS on desktop PCs will use the BIOS/EFI/UEFI.

All OS on the Raspberry must use start.elf and bootcode.bin etc.

ghans