Today's "PCs" (as in Windows/Linux/... x86-64 box) have little in common with an IBM AT. There's still some compatibility on the software level but the hardware is vastly different.
- Shugart FDD interface - gone
- ST506/MFM HDD interface - gone
- ISA bus - gone
- DIN-style keyboard interface - gone (still somewhat common with the compatible PS/2 connector - but vanishing)
- parallel printer port - gone
- 25-pin serial port - gone
- MDA/CGA/EGA video - gone
Even several successors of these vanished interfaces have gone:
- IDE/EIDE/PATA
- EISA bus
- VLB
- PCI bus
- parallel SCSI
- 9-pin serial port
- VGA video (15-pin)
Even the AT's BIOS that has incredibly long worked as a core for later BIOSes is increasingly replaced by UEFI.
Anything substantial left?