Disappearing memory on i7: I have an idea as to why

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07-12-2009, 08:19 PM
003

Disappearing memory on i7: I have an idea as to why

So for a long time now, there have been reports popping up from people running Core i7 that the detected amount of memory suddenly decreases one day, as if someone pulled out a stick or two of memory.

And there have been some confirmed and unconfirmed "fixes" to this problem being to reseat the CPU or the cooler due to contact with some of the pins becoming weak or lost.

Well I have a theory as to why this might be occurring -- lapping.

The i7s seem to have a convex IHS, and when it is lapped flat, it changes the pressure distribution of the mounted cooler, and hence, may affect the contact that the CPU makes with the pins on the motherboard. Does this seem plausible? Of course, if it turns out that multiple people who experience this issue do not have lapped CPUs, this idea goes down the drain.
07-12-2009, 10:02 PM
BulldogPO

I´ll think that it is too soon to think like that kind of situation.
People just need to boot with one stick at the time and check what is causing it.
07-12-2009, 10:25 PM
003

Quote:

Originally Posted by BulldogPO

I´ll think that it is too soon to think like that kind of situation.
People just need to boot with one stick at the time and check what is causing it.

Noo.. this theory is dead but the issue lives on.
07-12-2009, 10:54 PM
fallwind

There's 1366 pins in an i7 socket and all it takes is one of them to go out of alignment and you can lose a DIMM slot. It happened on my DS4. I changed CPU's and when I booted up, 2GB of RAM was missing. If I fiddles with it enough it would come back but it wouldn't last so I RMA'd the board.

A couple other things: more pins in the socket means less pressure per pin to maintain contact. Also, most i7 sockets I've seen have a bit of play in them when you set the CPU in it. So there can be a small variance in the position of the CPU when you lock it down.
07-13-2009, 03:27 AM
The-Fox

Quote:

Originally Posted by 003

So for a long time now, there have been reports popping up from people running Core i7 that the detected amount of memory suddenly decreases one day, as if someone pulled out a stick or two of memory.

And there have been some confirmed and unconfirmed "fixes" to this problem being to reseat the CPU or the cooler due to contact with some of the pins becoming weak or lost.

Well I have a theory as to why this might be occurring -- lapping.

The i7s seem to have a convex IHS, and when it is lapped flat, it changes the pressure distribution of the mounted cooler, and hence, may affect the contact that the CPU makes with the pins on the motherboard. Does this seem plausible? Of course, if it turns out that multiple people who experience this issue do not have lapped CPUs, this idea goes down the drain.

Your theory is most probably incorrect as I know many people, including myself, which encountered this issue and none of them lapped their CPU.

The problem is related to the contact of the CPU with the pins in the socket.
Because the CPU has an IMC, as opposed to previous Intel CPUs where the Memory Controller was in the NB, sometimes bad contact causes to one of the memory channels to drop/lost.
Usually pulling the CPU out and then back in solves this issue.

If the issue is constant, it usually means you IMC/Uncore is damaged, usually due to exceeded DRAM voltage (0.5v limit was not maintained between DRAM and QPI/VTT voltage.)