[SOLVED] i7 870 cannot see all memory but i3 540 can. CPU issues?

[amissipot21]

(Not sure if this is the right place to ask about such legacy hardware (i7 first generation and an old motherboard). Please, let me know if there I should ask this somewhere else.)

I have an old computer:

Motherboard: Asus P7H55-M
Processor: i3 540
RAM: 4 GB DDR3

So, I decided to upgrade it to 16 GB RAM and upgrade processor. I bought 3 more DDR3 banks, each 16 GB each. They worked pretty fine with i3 540 and I've used the computer for some days. Them, I upgraded processor to i7 870. This processor requires an external video card (which I plugged into the computer as well). Everything worked fine, but, it only recognizes half of RAM.

The motherboard has four DDR3 slots and, according to the manual, they are divided into Channel A and Channel B. From experimentation, it seems that CPU cannot "see" memory from Channel B, hence it only sees 8 GB out of 16 GB. Surprisingly, if I downgrade it to i3 540, it sees all 16 GB!

Yes, I updated BIOS to the latest version.

I have searched about this problem, but found nothing related to the motherboard nor the CPU itself.

Have you ever seen anything like that?

Thanks!

 

[Loadedaxe]

So, I decided to upgrade it to 16 GB RAM and upgrade processor. I bought 3 more DDR3 banks, each 16 GB each.

I am going to assume you meant 4GB sticks for a total of 16GB, correct?
I am going to go out on a limb here without seeing the computer but it seems the memory controller on the i7 is defective. To test this theory, take the sticks from channel a and install them into b, make sure no sticks are in channel a, boot pc and share results.

 

[amissipot21]

I am going to assume you meant 4GB sticks for a total of 16GB, correct?

Yes! Sorry for my bad English.

Thanks for the reply. I have made the test you told me to do and some more that I summarize in the following table:

Test (using 4 GB sticks)	i3 540 recognizes...	i7 870 recognizes...
All 4 sticks inserted (4GB each)	16 GB	8 GB
2 sticks inserted in slots A1, A2 (black, blue)	8 GB	8 GB
2 sticks inserted in slots B1, B2 (black, blue)	8 GB	no video output
1 stick inserted in slot A1 (blue)	4 GB	4 GB
1 stick inserted in slot A2 (black)	4 GB	no video output (*)
1 stick inserted in slot B1 (blue)	4 GB	no video output
1 stick inserted in slot B2 (black)	4 GB	no video output

* it is an interesting thing: for i7 870 I have to have a stick inserted in A1 for all cases, so I get no video output at all, which doesn't happen when I use i3 540.

I see no other explanation other than it is a defective CPU, right?

Thank you very much.

 

[amissipot21]

Oh, one more thing. All 4 4GB sticks are Kingston KVR1333D3N9/4G. A friend of mine told me that there can be compatibility issues between i7 870 and these memory sticks, although I think it is very strange. Anyway, it is true that i7 870 is a bit older (September 2009) than i3 540 (January 2010).

 

[Loadedaxe]

It could be compatibility issues, unless are all the memory sticks the same spec?
Yes the i7 is older but not that much older. I would venture to say its a bad cpu.