Not exactly true. […]
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Not exactly true.
The original BIOS was indeed, a combination of an IPL (Initial Program Loader) and a toolkit of useful IO service routines.
To say it was never extended though, is just wrong. Some noteworthy modifications/extensions to old fashioned BIOS are the many INT13 improvements, El Torito and USB booting, USB Legacy support for keyboards and mice, fancy new chipset features, including PCI CLK and pals, Plug and Play extensions, and many many more.
The actual thing that happened, was that Intel and Pals decided (tm) that its days were over, and switched whole-hog to the New!(tm) Universal Extensible FIrmware Interface. (UEFI)
This does not start the processor in real mode anymore, (which Intel REALLY REALLY WANTS. They have wanted to axe realmode for over a decade now, and have wanted very hard to not have back-compatible ISA for even longer. Remember Itanium? I DO! Remember Pentium-Pro before that? I DO!)
The MAIN selling point of UEFI is that it starts immediately in flat mode, and can supply more sophisticated services (like straight up ethernet stacks, audio processing stacks, complex biometrics bullshit, you name it), and allows the CPU to better do fancy shit with its spiffy new Secure Enclave, (Trusted Platform Module, and the Secure Enclaves baked into Intel and AMD processors, respectively) and to be able to deal with GPT partitioning, so that it can handle modern "Its ENORMOUS!" disk drives.
However, this means old legacy utilities and routines are "NO LONGER NEEDED!!", so, you see only the most vestigial trappings of such things on these systems. Just enough to display video before the GPU driver loads, etc.
Since CSMs are no longer being baked into UEFI firmwares, legacy DOS support is becoming more and more impossible to pull off outside of emulation.
The afore-mentioned SoC I wasted 6 posts on, uses only UEFI out of the box. It was DESIGNED this way, as it is an Intel product, designed by Intel, and pushes the "NO, WE HATE THAT!!" philosophy. They even tried to go so far as to claim it was not actually a "computer", and was instead a "Hobby Platform". This is WHY I wasted 6 pages, answering how to gut that UEFI firmware out, and get a FOSS minimal BIOS on instead. (Coreboot + SeaBios).
Still lacks a suitable audio chip, but it could potentially be convinced to have one. (On the underside, is a compact high-density header that has a PCIe 1x lane, which could have a PCI bridge chip put on it, and a PCI Soundblaster clone. I wont hold my breath-- the MinnowBoard is EoL, out of production, (but DOES have FOSS published Gerbers, so if somebody wants to have some made, they CAN....) and did not sell well when it WAS in production. It cost too much, and was crippled from the gate for what most enthusiasts would have wanted to do with it, due to Intel's characteristic lack of vision on what the market wants. (VS what THEY want.)
Regardless, we are stuck with Intel's lacklustre future with UEFI for the foreseeable time being.