Ok this may sound absurd or weird (or both lol) but I’ve been curious for quite a while now about what powers a BIOS chip? I get it, it must be some sort of code or programming but how exactly does a BIOS chip come to life (which then powers a PC / laptop, for example)? Like is there some sort of a master device or a piece of code that you just insert into a piece of metal & plastic?
P.s.: I’m REALLY hoping someone actually reads & replies. Thanks in advance guys!
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A BIOS chip is just a non-volatile memory chip. It responds to an address input by outputting the data stored at that address. Like all devices attached to the system bus it needs to respond to a certain range of addresses. For example 32-bit Intel and compatible AMD CPUs require that BIOS be located at 0xFFFFFFF0 address and below because the very first byte CPU reads once powered is at 0xFFFFFFF0 address. If for example you have a 16 MB BIOS storage chip you need to make it respond to 0xFF000000 – 0xFFFFFFFF range of addresses. To do that you need an additional chip that checks if the upper 8 bits on the address bus are all ones. If they are then the chip should enable “Chip Select” pin of the BIOS storage chip. “Chip Select” disables/enables the whole chip. That’s it. You now have a device that can boot (after you write the BIOS code to the chip of course).
As for the BIOS code, it’s kind of super stripped-down operating system with built-in primitive device drivers and ability to run a single built-in application without any memory protection like in a real OS. Once it’s finished it passes control to the real OS and turns itself into a library (a passive collection of code and data) that the OS can optionally use to communicate with devices in a limited way.
I wouldn’t say BIOS powers a PC / laptop. It just initializes the builtin devices and tells the OS the configuration parameters of the devices. You could in theory completely get rid of BIOS and just have a small invisible to user bootloader. ARM based Android phones run a real Linux-based OS without any BIOS.
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