Been quite a few years since I last dug in the subject, but from what I remember, Sony used for the PS1 an emulator called "POPS", and Sony up to the Vita added hardware from the previous generation into the new console, but I don't remember any mentions of them adding hardware further than a single generation.
And a surprise to me, but apparently according to this wiki (cw: Fandom), the PS3 used some degree of emulation even for the PS2. Rather curious as to run PS2 games, the PS3 boots into a PS2 mode, which feels almost like a dual boot.
entropicdrift@lemmy.sdf.org 1 week ago
They embedded a PS1 in the PS2, but the PS1 compatibility for the PS3 and later is emulation. Also the PS2 compatibility for most of the revisions of the PS3 is emulated too. Only a couple of the earliest models crammed a PS2 in there