Coffee Lake in old LGA 1151 (H4) socket

hardware_failure

[H]ard|Gawd
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Mar 21, 2008
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I have a handful of HP EliteDesk 800 G3 w/ Motherboard 906309-001, LGA 1511. Stock with Skylake i5 6500T. I was able to get one to boot with an i7 6700 (also Skylake) but not an i7 8700 (Coffee Lake). Bios beeps 3 short 5 long. (interwebs mention 4 long but no 5) I know that intel redid socket 1151 for the newer Coffee Lake 6/8 core procs - but interwebs also said new 1511 was redone to support intel Optane memory. The bios DOES mention Optane memory. Are 2nd revision LGA1151 ever at all backward compatible with previous generations?

Also interestingly had to use a 90w power brick for the 6700 vs 65w (65w TDP chip vs 35w I guess)

I have only the one spare 6700, but lots of 8700's and so far no way to use them...

Thanks!
 

Absalom

[H]ard|Gawd
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Are 2nd revision LGA1151 ever at all backward compatible with previous generations?
Officially? No. Intel never intended them to be backwards compatible.

While Kaby Lake and Skylake and interchangeable with their respective platforms, Coffee Lake broke compatibility with what is known as the 100 and 200 series motherboards. The pin counts are the same, but some pins were repurposed for power and grounding of the new chip. Effectively, 8000 series cpus are not electrically compatible with predecessor platforms. By that same token, the 300 series and newer motherboards are not compatible with the 6000 and 7000 series cpus either.

There is no software solution (i.e. BIOS update) for what is essentially a hardware issue.

I know that intel redid socket 1151 for the newer Coffee Lake 6/8 core procs - but interwebs also said new 1511 was redone to support intel Optane memory. The bios DOES mention Optane memory.

Optane got mainstream support via introduction of the 200 series chipsets (i.e Kaby Lake), and given what I stated already, Optane support alone would be a poor indicator of cpu compatibility.

You'll need boards using a 300 series chipset or newer to handle those 8000 series cpus.

Unofficially? Technically some loons have claimed to have gotten them to work.
 
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hardware_failure

[H]ard|Gawd
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Thats too bad, but thanks for the insight.

The bad: I have no idea how to edit a bios (other than changing the post logo once like 10 years ago) but the good is I might know a guy and I have a few of these to burn so if I brick one NBD.

Thanks again.
 

XoR_

[H]ard|Gawd
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I planned on using 9700K with Z170 board with DDR3 memory taken straight from my Z77 mobo. Should be pretty interresting system and even if not as fast as 9700K on fast DDR4 it would be almost as fast for much cheaper. Went instead with 9900K on Z390 and DDR4.

The mod itself requires making Coffee Lake CPU electrically compatible with older LGA 1151 socket which translates to isolating some pins and making bridges. It didn't look too complicated but not for the faint of heart either. It didn't require cutting socket like LGA771 to 775 mod and I did such mod so I would probably manage.

Other thign this mod requires is BIOS modification and here you have to add microcode for the new CPU you want to install but also for some CPU's there is a need to update some ACPI/APIC (or however it was called) code to support more threads. 9700K having only 8 threads doesn't require this modification making it easier target. 8700K might require it and if it does depends on what is inside your current BIOS. From reports on internet from people who tried it 9900K with 16 threads is more problematic as 8700K did work with some boards which 9900K didn't... maybe I remember it wrong though. Another issue is power. Especially 9900K might be too much to handle by some motherboards - it has twice as many cores as 6700K/7700K! 8700K has 50% more cores so it should be safer. Still I think without OC these CPU's should work just fine.
 

Macho

Weaksauce
Joined
Jul 26, 2020
Messages
78
I have a handful of HP EliteDesk 800 G3 w/ Motherboard 906309-001, LGA 1511. Stock with Skylake i5 6500T. I was able to get one to boot with an i7 6700 (also Skylake) but not an i7 8700 (Coffee Lake). Bios beeps 3 short 5 long. (interwebs mention 4 long but no 5) I know that intel redid socket 1151 for the newer Coffee Lake 6/8 core procs - but interwebs also said new 1511 was redone to support intel Optane memory. The bios DOES mention Optane memory. Are 2nd revision LGA1151 ever at all backward compatible with previous generations?

Also interestingly had to use a 90w power brick for the 6700 vs 65w (65w TDP chip vs 35w I guess)

I have only the one spare 6700, but lots of 8700's and so far no way to use them...

Thanks!
I have had good luck with HP EliteDesk 800 SSF & MINIs. G1 & G2. I bought the un made motherboard, HP Z390, and got it up and running, but now a similar problem with 8 long beeps and no post and then it goes off. To get the 8 beeps I held the Windows key + B while booting. I just had the Windows update Bios update, and it did not
first back up the old bios. 20 minutes later after attempting to put the bios in UEFI mode from Legacy, it will now not post and just goes off like yours did, no matter what I do. I am using the Intel 9600k CPU in LGA 1511 socket. I thought to scrap the motherboard since all the motherboards are available since they did not make this Omen HP.
 
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