What are all those pins for? " Reenigne blog

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What are all those pins for?

I recently built myself a new computer using an Intel Core i7 920 CPU. This CPU has more pins (well, "lands" actually, since they are just flat conducting areas that touch pins in the socket) than any other yet produced, 1366 of them to be precise. I was wondering why so many were needed, so I grabbed the datasheet and made a map:

Power:

VSS

VCC

VCCPLL

VTTA

VTTD

VDDQ

Memory:

DDR0 data other

DDR1 data other

DDR2 data other

Other:

QPI data other

Other

reserved

Idle speculation follows (I don't have any background in CPU or motherboard design):

The pins roughly divide into six sections: two for memory data, one for other memory-related signals, one for power, one for the QPI bus and one that is mostly reserved.

That there are a lot of power pins is not surprising - this CPU can use as much as 145A of current, which is enough to vaporize any one of those tiny connections, so it has to be spread out amongst ~300 of them for each of power and ground. Having two very big pins for power would probably make the mechanical engineering of the CPU much more difficult and would push the responsibility for branching out that power onto the CPU, whereas it is better done by the motherboard.

It's interesting that the ground lands are mostly spread out but the power lands are mostly together. I'm not sure why that should be - I would expect them both to be spread out. Perhaps the 8 or 9 big groups of VCC on the north edge each correspond to a single "power line" on the motherboard (and hence are grouped together) while the distributed ground lands are needed to supply electrons for the signal lands.

Three DDR3 channels also use a lot of lands - 192 for data alone and almost as many again for addresses, strobes and clocks.

Another thing that surprised me is that there are so many reserved lands (~250 of them). Initially I thought that this was because the socket was designed before the designers knew how many pins they would actually need, so they made sure to design for the absolute maximum. However, a good chunk of the reserved lands are used by the Xeon 5500 CPUs, which use the same socket - in particular for memory error detection/correction and the second QPI bus (which is presumably in the northwest corner).

Edit 14th July 2013:

Here are some more nice pin maps.

This entry was posted on Wednesday, October 28th, 2009 at 4:00 pm and is filed under computer. You can follow any responses to this entry through the RSS 2.0 feed.

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42 Responses to "What are all those pins for?"

Impressive says:

February 25, 2010 at 8:52 am

Impressive amount of effort you put into the colour mapping. Very interesting post.

Would you mind if I used the image for my own personal use, non commercial?

Regards

Luke

Reply

Andrew says:

February 25, 2010 at 12:45 pm

Thanks! Yes, you can use the image. I would be interested to know if you do anything interesting with it.

Reply

Edward says:

April 30, 2023 at 9:27 pm

Great work! I'm trying to do the same for an old cpu, and was wondering how you came about in mapping it?

Regards

Edward

Reply

Andrew says:

May 1, 2023 at 8:08 pm

Thanks! I just wrote a quick and dirty program to process the information from the datasheet.

Reply

Paul says:

May 25, 2011 at 8:22 am

Very impesesd with your commitment. i have five pins on a used motherboard that according to your diagram are earths and power pins which are bent or missing. do you know if the cpu will still work ok (as there ar so many of these type on the board.

regards Paul

Reply

Andrew says:

May 25, 2011 at 9:34 am

I'm not sure. There are three aspects to this, only one of which you can check. The first thing is to check that the bent pins can't touch anything else. The second aspect is whether all the parts of the chip will actually get power. The earth and especially the power lines are probably connected up inside (since, from a chip design point of view, it's probably easier to do it that way than to try to make sure that no single pin transfers too much power) but if they aren't the chip won't work and could be damaged. The third aspect is whether the remaining pins can deliver enough power. There is usually some margin of error with these things, so it should be okay, but it's possible that when the chip is really working hard and consuming a lot of power, the remaining connections will get hot. That will increase their resistance, further limiting the power transfer. If there's too much power transferred and too few pins, this could lead to a runaway situation where the remaining connections burn up. Overall I'd say you have about 20% chance of destroying the chip, 10% chance of it not working properly and 70% chance of it working perfectly.

So I guess it depends on whether the...