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Comment by userbinator | Hacker News Reader

When I have x86 image of Windows/Linux, I can boot it on any x86 processor.

That is largely due to IBM choosing x86, and the PC taking off in a huge way with its de-facto "open" design that ended up being successful and kept backwards compatibility. One could easily imagine a world in which IBM chose ARM (and it was invented earlier) for its first PC, and proprietary x86 SoCs based on Intel's cores are everywhere instead. A world in which CISC is the new fad.

Note: Intel has non-PC-compatible x86 SoCs too.

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I'm curious what those would be in the modern era?

The "non-PC" x86 chips I can think of:

80186/188 - Sort of predates the IBM hegemony, can be hammered into shape by adding replacements for onboard peripherals 80376 - a failed long-gone experiment 386CX/EX - not entirely sure how incompatible they are Xeon Phi/Larrabee/Knight's Corner designs -- not really SoCs so much as special purpose acceleratirs.

I think the Moorefield and Merrifield SOC platforms are not PC compatible?

Also these: https://en.wikipedia.org/wiki/Intel_Quark

They are basically a 486 pipeline with some Pentium instructions.

Unfortunately it seems Intel didn't realise that x86 without the PC legacy is worth little, so their attempts at non-PC x86 have mostly failed. On the other hand, "PC-on-a-chip" SoCs like https://en.wikipedia.org/wiki/Vortex86 have enjoyed more popularity.

The PS4 (and probably PS5 as well) use x86 chips but are not PC-compatible.

This might be true, but the world we live in where x86 is the open platform and ARM is a mess of incompatibility.

You want to install Ubuntu on your laptop? Download this ISO and you're good.

You want to install LineageOS on your phone? You have to download the exact binary for your phone (which means LineageOS needs to maintain those hundreds of versions) and hope your phone is supported.

This is because your PC has a software compatibility layer called a BIOS.

The BIOS (or UEFI) is not used by most OSs which aren't DOS. The compatibility comes from the standard peripherals (DMA, PIT, PIC, FDC, 8042) and PnP interfaces like PCI (as well as standardised interfaces located behind them, e.g. USB OHCI/UHCI/EHCI/XHCI, SATA BMIDE, LPT, VGA, etc.)

The BIOS (or UEFI) provides a standard interface to load an operating system which can then discover which hardware is installed.

It's true that another factor is the software discoverability of hardware. A lot of stuff on ARM platforms is not discoverable because those platforms are intended to run specific software.

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