I think the largest computers I used extensively for sometime was the quadroplex HP V-Class V2600 my business bought back in 2002 or so:
Each cube was a V2600 computer with 32 PA-8600 552MHz 64bit processors and 32GB RAM, all coupled via a common ring bus to a large single image system running HP-UX (originally 10.20, later I used 11i v1). Connected to it was a separate HP9000 B180L+ 64bit Workstation, however after upgrading to HP-UX 11i I stopped using it and used a Thin Client to connect to the V2600 directly.
A few details about these systems can be found here:
https://openpa.net/systems/hp-9000_v2500_v2600.htmlThere were a few other big systems, like a Compaq/DEC AlphaServer 8400:
Or a couple of Siemens RM600E running ReliantUNIX:
There were also large machines from SGI (Challenge XL, Onyx XL, Origin), Sun (E10k, E3500), IBM (RS/6000 SP2) and lots of the mid-size and smaller machines.
These days my largest personal desktop PC is a HP z840 with two 8-core XEONs and 512GB of RAM: