Adding RAM to HP EliteDesk 805 G9

[Justric]

Hello, I would like to add ram to my HP EliteDesk 805 G9 SFF desktop. There is 64GB (2 -32GB) currently installed, and 2 slots available. When I purchased the PC, the specs said the RAM capacity is 128 GB. I tried adding 2 more 32 GB DDR5-5600  UDIMM (Crucial) memory sticks to the other 2 slots but the machine won't boot up now. I then tried removing the original two memory modules and replace them with the crucial modules, in the same slots as the original ram, and it still won't boot up. 

According to the specs for that desktop, it comes with DDR5 5600 MHz ram installed. In fact, it appears that the installed RAM on the machine I purchased is noted as PC5 4800 32GB modules. I am trying to understand why the PC will not boot up at all when I install the DDR5-5600 ram modules - either with the others installed or not. Anyone have any ideas on that?

Thank you.

Ric

[NonSequitur777 · Accepted solution]

@Justric,

Welcome to our HP Community forum!

HP EliteDesk 805 G9 SFF – Your System Won’t Boot with Crucial DDR5-5600 UDIMMs? Here’s Why:

You're right to be puzzled, especially since HP advertises support for up to 128GB (4x32GB) DDR5-5600 memory on the HP EliteDesk 805 G9 SFF -and you used 32GB × 2 Crucial UDIMMs that appear to match the spec.

Let’s break it down and explain why the system fails to boot:

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Key Issue: RAM Voltage and Compatibility:

HP’s specification lists supported RAM as:

SKO-UDIMM DDR5-5600 1.1V NECC (e.g., HP Part No: N77570-001)

 

Your Current Working RAM:

• Likely uses JEDEC-standard 1.1V low-voltage non-ECC DDR5 memory, possibly custom-binned or vendor-qualified SK Hynix, Micron, or Samsung modules.

• It runs at 4800 MT/s by default unless XMP/EXPO or equivalent tuning is applied -which OEM systems like HP typically do not support in BIOS.

 

Your New Crucial RAM:

• Although labeled as DDR5-5600, many Crucial consumer UDIMMs default to 1.25V or higher to reach 5600 MT/s via XMP profiles.

• HP BIOS does not support XMP, nor does it allow adjusting RAM voltage or timings -so non-JEDEC modules may fail to POST entirely, even when installed alone.

---

Why It Won’t Boot — Even Alone:

Crucial’s DDR5-5600 modules likely require XMP to reach advertised speeds. Without fallback support for JEDEC-standard 4800/5200/5600 at 1.1V, the system cannot initialize memory at all. That's why it hangs or fails to power up.

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What You Can Do:

1. Use Only HP-Qualified or JEDEC-Compliant RAM
   Look for DDR5-5600 UDIMMs that explicitly state:

   • JEDEC 1.1V such as: https://www.amazon.com/Crucial-4800MHz-Desktop-Memory-CT32G48C40U5/dp/B09HW6ZJV5/ref=sr_1_4?crid=2UG....

   • Non-ECC, Unbuffered

   • Non-XMP dependent
     → HP or Kingston “ValueRAM,” Crucial Pro Business, or Micron JEDEC RAM are safer bets.

2. Avoid Consumer Gaming RAM
   If the module says "XMP" on the box or requires BIOS tuning to hit 5600 MT/s -skip it for OEM business-class PCs.

3. Match All Modules
   For maximum stability, especially with 4 DIMMs:

   • Same brand

   • Same voltage (1.1V)

   • Same primary timings

   • Same rank and capacity (ideally 4× identical sticks)

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Additional Notes:

• Your original 32GB modules showing PC5-4800 is expected -HP often ships JEDEC 4800 MT/s by default.

• Even if the motherboard supports 5600 MT/s, it will typically run all four DIMMs at a lower speed (often 4400–4800 MT/s for full population).

Kind Regards,

NonSequitur777

[Justric]

NonSequitur777, 

Thanks for that detailed and precise response. I will be returning the RAM modules i bought and will buy those you suggested. I did note the Crucial ram modules i purchased have 1.1V noted on the label, but obviously that in itself is not enough, and the support for XMP and other factors also come into play, as you pointed out. I really appreciated your response to my dilemma.

Justric

[NonSequitur777]

@Justric,

You're quite welcome: please follow up with your RAM experience as it will help somebody else out there!

Kind Regards,

NonSequitur777