HP Proliant 585 G2 from 2007. It has 4x6 AMD Opterons 8xxx with DDR2 etc. I guess it is no longer cost effective to run those 24/7, but they are still very powerful.
Old CPUs without power savings features are great for testing multi-threaded applications. Modern CPU might decide to switch-off some parts during test, rendering result inconclusive.
This beasts power requirement looks scary, but with some care it runs in ordinary house. I use separate AC circuit usually used for air-conditioning. It is very loud (like hoover). I usually run it about 30 minutes a day.
I work on concurrent Java stuff. Fork-join, CAS, low latency databases etc. I mostly use this machine to verify things I read somewhere. I found that about 60% of things I read about concurrency is wrong. For example messaging (actors) are not really that great compared to well designed threads with locks & CAS.
Right now I want to replace memory allocator with global lock (linearly scales up to 6 cores) with CAS version, which should scale up to 16 cores.
Interesting way of finding something to do with those! I've also been intrigued by the old Proliants on eBay, because the prices seem quite cheap initially: $250-400 for massively multicpu things with tons of RAM. But I've been scared off each time by a mixture of the weight and power usage. One listing even specified that delivery would be made to your loading dock (sadly I do not have a loading dock), although that was for a big Itanium machine.
