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> can you even have something similar to IBM PC with ARM? AFAIK, ARM does not have port mapped i/o, so that makes it difficult to really match up with the PC. That said, an OS can require system firmware to provide certain things and you get closer to an IBM like world. Microsoft requires UEFI for desktop Windows (maybe WP8 and WM10 as well, but I believe those were effectively limited to specific qualcomm socs, whereas I feel like Desktop windows is supposed to be theoretically open to anything that hits the requirements). ACPI for ARM is a thing that exists, but not all ARM systems will have it. Technically, not all x86 systems have it either, but for the past several generations of Intel and AMD, all the hardware you need for ACPI is embedded in the CPU, so only old hardware or really weird firmware would be missing it. Also, PC i/o is so consistent, either by specification or by consensus, that it's easy to detect hardware anyway: PCI is at a specific i/o port by specificiation; cpu ID/MSR lets you locate on-chip memory mapped perhipherals that's aren't attached via PCI, and PCI has specificied ways to detect attached hardware. There's some legacy interfaces that aren't on PCI that you might want, and you need ACPI to find them properly, but you can also just poke them at their well known address and see if they respond. AFAIK, you don't get that on other systems... many perhipherals will be memory mapped directly, rather than attached via PCI; the PCI controller/root is not at a well known address, etc, every system is a little different because there's no obvious system to emulate. Mostly ACPI is about having hardware description tables in a convenient place for the OS to find it. Certainly standardized understanding of power states and the os-independent description of how to enter them is important too. There are/were other proposals, but if you want something like UEFI and ACPI, and you have clout, you can just require it for systems you support. The market problem is Apple doesn't let their OS run on anything non-Apple, and Android has minimal standards in this area; whereas the marketplace for software for the IBM PC relied heavily on the IBM BIOS, the marketplace of software for Android relies on features of the OS; SoC makers can build a custom kernel with the hardware description hardcoded and there's no need to provide an in firmware system of hardware description. Other OSes lose out because they too need custom builds for each SoC. |