There were a lot of computers that worked without BIOS.
I can only speak for DEC.
The computer series from DEC, via COMPAQ today at HP, all mini and midi computers of the series dec PDP-8, PDP-11, VAX, Alpha have no BIOS.
From the PDP-11 series, all device registers of the various HW controllers were mapted into a memory area reserved for the IO.setting up an HW register was nothing more than describing a memory location. Very efficient. Very simple.
In order to avoid a mess, the memory management systems HW had to prevent any process from writing to a device register without having the necessary authorization.
These permissions were granted by the OS.And this largely granted these permissions only to the device drivers, which were part of the respective OS. DEC RT-11, DEC RSTS-E, DEC RSX-11M, DEC VMS … DEC UNIX.
Thus, every IO request and every IO query of an application had to go via the device drivers of the OS.For this purpose, a QIO block (memoryblock) is applied in a real-time multi-user system such as RSX-11M or OpenVMS. This is written to an IO queue and then retrieved and executed by the device driver. The result is returned to the caller in a similar way as an IO status block.
This was also the time of the Asynchronous System Traps (AST), a SW-forced type of interrupt that could interrupt other processes such as the correct HW interrupts.
This is still the case with many OS even today, but then many device drivers call the BIOS (Basic Input Output System) for help with the implementation.
The good thing about the BIOS is that once an HW card has hooked in, this card can be called up at relatively narrow ports.The BIOS thus regulates the HW specic special features and the device drivers the OS specific. Together, they thus form the part of the computer’s SW responsible for the IO.
And if the parameters have entered the BIOS via this BIOS port, a BIOS that is HW specific, is different from manufacturer to manufacturer, only this BIOS knows what to do with the parameters data, the registerdata.
In this way, the device drivers of the various OS can be freed in part from the necessary deeper knowledge of the thousands of HW controllers and HW interfaces.This is proven by the many OS specific device drivers.
As a result, the BIOS must be OS independent.And the things that depend on the OS of the IO functions belong in the OS specific device drivers.
In summary: The BIOS implements the HW specific, manufacturer-specific things that device drivers the OS specific things.
Computers that do not have a BIOS therefore need to implement the HW specific knowledge necessary to operate a device in the OS/HW-specific device drivers, which greatly increases their scope and complexity.