@kenshirriff There's also P54CS and P54CQS, but I don't know what the letters mean, sorry - way before my time.

The original P54C was done in Intel's in-house design language, which was then retired in the 90s I think. Fortunately the design had been ported to more modern design languages like VHDL or Verilog in the meantime, so then we took that version, ported it yet again to the absolutely newest language that Intel was using.