Recently I was given a macpro 2,1. A genuine one, not flashed. It was in the junk pile of a computer shop, with a paper stuck on it saying it needed the motherboard replaced. I am always leery of diagnosis like that, many times I have seen they are wrong. When I received it, it had no ram, two 500gig disks, no dvd or dvd caddy, no vid card, also the wifi module had been removed. The ID sticker on it shows it was pretty impressive when new: Mac Pro/3.0_8CX/8x1/x1900xt/250/500/500/500/2xSD/AP/BT/APRTR I installed some ram I have from a 1,1, an apple 5870, and tried to boot it off a hard disk preloaded with ElCap from a 1,1. It would turn on, then reset itself about every 4 seconds, never chiming. I tried pulling out the lower ram riser, and it booted right up to the desktop with no errors. I ran some tests, even ran geekbench a few times, all seemed ok. I have four sets of 1,1 ram risers, so tried some others, and it would not boot with anything in the lower bay. So, I was planning to just run it with 8gig in the upper riser until I manage to find another motherboard. I took it apart to clean it, removing the fans, ram box, and heatsinks cover, to give it a thorough cleaning. It came out great, and looked suitably shiny inside. While doing the cleaning, I noticed the many differences between the 1,1 mac pro, and the 2,1. Many people think they are the same, with only firmware and cpu's changed, but thats completely wrong. I'll put a list at the end of this with the changes I noticed. The 2,1 seemed to be running fine, but after about a day of random use, and benchmarks, it suddenly reset itself, and would chime, then reset, chime, reset, etc. I guess something else died on the motherboard. With a frown, I took out the useful parts I had added, and put the 2,1 in the attic, to await the chance I find another 2,1 for its motherboard. After talking to LightBulbFun about it, and remembering that he had flashed his 1,1 to the 2,1 firmware, I had an idea: I have three working 1,1 mac pros, and figured it was worth risking one to fix the 2,1. I flashed one of my 1,1 to a 2,1 with no problems, ran some tests, and whatever I could think of to make sure it was working properly. I did not flash the SMC. I then removed its motherboard and set it aside for transplantation into the 2,1. Bringing the 2,1 back down from the attic, I figured i would just take it apart, swap motherboards and be up and running... due to the changes from 1,1 to 2,1, that was not quite how it went. A big problem I came across was taking out the 2,1 heatsinks. They are not exactly like the ones in the 1,1 and are actually closer to the 3,1 versions, with 3 full length heat pipes on each one. They also have added in parts for their mountings, plastic blocks under them to help support them on the motherboard, and metal mount tabs built into the motherboard to help center them. The 1,1 does not have these features. The lower heatsink temperature sensor also plugs into the motherboard at a different location on the 2,1 vs the 1,1. Further, the heatsinks were STUCK to the cpu's. I mean REALLY stuck. They used that wierd silver compound stuff with the gaskets that apple used only on the 2,1. The heatsinks were so stuck, that removing them required so much force that it bent the cpu socket clamps, and made an aweful sound like the cpu socket nearly ripped off the motherboard. Anyway, they came off, and I didnt see any damage on the heatsinks or the tops of the x5365 cpu's. The 2,1 heatsinks will work on a 1,1 motherboard, you just have to remove the plastic blocks, and use the 1,1 mounting brace thats on the backside of the board. I couldnt get the silver stuff off the heatsink base, or the cpu tops, so I left it there, and used a super thin layer of arctic silver to join them back. It seems to have worked. The 1,1 board fit in the 2,1 case with no problems. The 2,1 motherboard is different, but the changes are all around the cpu's, and at the front right behind the front panel module. The main cable connections are all the same. I added back the wifi module, using one from a macbook pro 3,1. It is the 3 wire type. After putting it all together, the 2,1 booted right up with 16gig ram using both risers. I have run Lion, and ElCapitan on it with no problems, and ran several benchmarks. Also tried a two drive stripe raid. Geekbench score was 1693 single, and 11720 multi in ElCapitan. Its been on all day, running various apps and just playing around with it, it seems to be running well with no problems. I do notice that the first two ram slots in the upper riser run pretty hot. With any use the fbdimms in those two slots hit 78-80c. The SMC seems to be working ok, when the ram hits 80, the fans will speed up to 1500 until they drop to 75. My guess is the 150 watt cpu's are making the air blown over the ram hotter, so causing them to have higher temps than I saw in the 1,1 system. So the changes I noticed from 1,1 to 2,1 were: PSU cables covered with a plate, like on the 3,1. Motherboard is physically different. CPU heatsinks are physically different, but very similar to a 3,1. Black speaker mount in the bottom of the case is like a 3,1. Front fan unit has the lower mounting screw like on a 3,1. CPU heatsinks cover plate is held on with magnets like a 3,1. So, just wanted to share, info might be useful to others working on a 2,1 mac pro.