do you know what its comparable to?
If you have a board for it, CPU-Z will tell you what it is. If not, there should be a gold 5 digit number near the edge of the heat spreader. This is the package number, and can be compared to to known production chips (Google for pictures of Opterons, check ebay,...).
You already know it's 2.1GHz quad core, so it's almost certainly either Barcelona or Shanghai. By the low speed, I'm guessing Barcelona. The good news is it will have an unlocked multiplier.