My p 70 is Xeon E3 1505M wich is supposed to support ECC, and 8gb memory. I bought 3rd party memory, Crucial ddr4 2400 ECC, and installed it. As you guys know about the problem with ECC, which is impoosible to enble ECC, I will skip that problem. My main problem is if I removed the original memory, and installed the new one from Crucial. This computer doesn't start up. Just turn on the light of switch and turned it off itself.

I understand this machine cannot support ECC now, but it doesn't mean don't start up with it, right? I thought it is something wrong, so I made a call to tech supports, and he told me it is common sense that 3rd party memory doesn't work. Now I have no idea. What should I do excpet for "you shouldn't buy Lenovo"?

Not that I'm excusing the P70 not starting, but I'm sure the issue is that the "designed" memory is DDR4-2133, not DDR4-2400.  If you have at least one stick of DDR4-2133 (i.e. factory-provided memory from Lenovo, by either Samsung or Micron) the BIOS will "slow down" faster memory to run at the same speed as the slowest memory you've got installed.  So as long as you have the Lenovo memory installed, your 2400 memory will be slowed to 2133 speed.  And I guess with all your memory running at the CPU-intended speed there is no problem.

Obviously, without the Lenovo memory present but only with the 2400 Crucial memory present, the BIOS may be trying to run things at 2400 speed, which apparently is a no-go.  You'd think the BIOS-performed slow-down to the one-and-only designed 2133 speed would occur no matter what memory is installed, if it's that critical.  Obviously not.

This is not true. I have two Hyperx 2400 8Gx2 in my P70, it works flawlessly. I should note that I have 6700HQ CPU inside. Look forward to Lenovo's response.

It is not a perfect machine but definitely meet my expectations and needs. Just a little more work, Lenovo.

Well, your memory is not ECC. And you don't have a Xeon CPU.  So clearly there's something quite different going on down in the BIOS under those other circumstances, when there is not an explicit 2133 memory stick present.

What speed does CPUZ say your memory is running at?  2133? Or 2400?  Did the BIOS slow down your all-2400 memory to 2133?  Or is it actually running at 2400?

I don't have a P70 rather a P50 but I have had many memory issues.  It turns out that Skylake motherboards have been having problems with early-batch Hynix DDR4 memory chips.  Many "assemblers" of memory, apparently including Corsair in their ValueSelect line which I bought, have used Hynix memory chips.  (Hynix is the second largest producer of memory in the world after Samsung.)  Non-Hynix memory appears to be fine.  Also, as noted above, the Xeon machine, which I also own, does not ship with ECC memory, rather standard unbuffered, non-ECC, memory.  I think both Micron and Samsung memory chips work fine in our machines. 

Well first of all, the P50 does indeed ship with ECC memory because my P50 has it, 16gb stick as ordered from Lenovo.  And it doesn't work as ECC memory, which all tests indicate. Secondly, are you saying that Crucial uses Hynix memory chips, because the original post here was about Crucial DDR4-2400 (which I have also) not Corsair memory.

That's very interesting because it would explain all of the problems I was having.  However, I typed in the module number from the Samsung memory in my machine, which shipped with the Xeon, and it came up in a search engine as unbuffered, non-ECC memory.  However, the numbers were not exact, but very close (M471A1G43DB0-CPB).  I'd love to be wrong here, because mixing ECC and non-ECC memory would certainly explain all of the problems I had.

Second, Crucial does not use Hynix chips, rather they make their own Micron Technology memory and then market it under the Crucial brand.  As I understand it, the Xeon processor does not recognize any memory faster than  2133MHz (PC4 17000) memory, even if you install it.  The Crucial DDR4-2400 ECC memory is listed as backwardly compatible but it would run somewhat slower because of the parity bit and error checking, which I do not want.

Do you happen to know whether the Xeon is set up from the factory to use ECC?  if so, I'd *love* to be wrong because that would easily enable me to solve my problem.  Lenovo is sending me a brand new machine which is arriving tomorrow as mine has been in Atlanta twice, the last time for more than two weeks.

My P50 (very similar in specs to yours - but with Win 7 pro) was ordered and came with a 16gb ECC stick. The numbers on the stick do indicate that it is ECC (M474A2K43BB1-CPBQ). However, ECC is definitely NOT WORKING as has been established at other places on this board. 

I've since added 3 additional sticks of the Crucial DDR4 2400 ECC memory (PC4 19000) to bring it up to 64gb. Of course, the Crucial memory is now running as DDR4 2133 because of the Lenovo memory in the first memory bay (see DSperber's comment above), but that's quite fine because the machine is schreaching fast in everything I need it for.

Lenovo has been (understandably?) silent regarding ECC not working, imho. It could be a motherboard design flaw which will never be fixed for those who already have it, or possibly heat-related when enabled (?). It must be serious because they haven't acknowledged the problem and it is pretty obvious it doesn't work. Meantime, we've all been left to just try and figure this out. In Lenovo's defense, this could be a pretty obscure problem that is probably only fully understood at the design level and everyone else within Lenovo is just going off of the specs.

I get the impression that Lenovo really has nobody you can reach who really understands the machine at a technical level.  They can replace parts, or send you a new machine; but, when you want to *understand* what is going on, you can't reach anybody who can help you.  (This is not unique to Lenovo.)

Fortunately I do not need, or require, ECC.  I finally found somebody who claims to have, in stock, the Crucial Technology 16 GB kit I need.  I am simply going to remove the Samsung module which shipped with the machine.  Crucial told me that adding the memory in matched pairs is approximately 12% faster than adding the same memory but from different lots.  Mixing brands would presumably be even slower.  Also, they said that memory modules only play well with other brands about 80% of the time, which is a higher percentage than Corsair estimated.  At least Crucial has actually tested their memory with a live P50 and guarantees it to work.

I agree with you regarding problems with Skylake.  They also seem to have some problems with NVMe, in both destops and notebooks.  I guess this is what life is like on the bleeding edge. 

I forgot to add that, if you go to the Intel site, under the Intel® Xeon® Skylake® Processor E3-1505M v5 processor it states:

[ECC Memory]

‡ This feature may not be available on all computing systems. Please check with the system vendor to determine if your system delivers this feature, or reference the system specifications (motherboard, processor, chipset, power supply, HDD, graphics controller, memory, BIOS, drivers, virtual machine monitor-VMM, platform software, and/or operating system) for feature compatibility. Functionality, performance, and other benefits of this feature may vary depending on system configuration.

so it is possible that Lenovo did not choose to deliver ECC support.

I ordered ECC memory (can be done with a Xeon only). Now I learned that it does not work. It is like buying a car with additional airbags that are not connected to the crash senor so they never work in case of an accident.