alt Hacker NewsI cracked into many x86-based arcade machines (and non-arcade gambling machines), and none of them used anything really bespoke. I never seen non-BIOS/UEFI x86 system in my life.
Not going to say they are non-existent, but probably the only mention of not using UEFI on Intel chips was in the presentation of Linux optimization for automotive from Intel itself, where they booted Linux in 2 seconds from the cold boot.
I've seen the Intel bare-metal stuff in enough automotive products to call it extant in the wild; I've only heard of it being used in video arcade stuff so maybe I was misinformed there.
Anyway, I think we're both on the same page regardless that TPM and hardware root of trust are not the same thing. In some configurations TPM can (weakly) attest that the hardware root of trust is present, but it doesn't actually do any hardware trust root, and that looks architecturally very similar on x86 to how it looks anywhere else (mask ROM verifies a second bootloader against RTL or manufacturing fused chipmaker public key hash, second bootloader measures subsequent material against OEM fused key hash, and so it goes).