HP EliteDesk 800 G5 Small Form Factor PC upgrade guide

Lifecycle and support

Standard support ended on February 2026 (estimate).

Dates not listed haven't been published by the manufacturer or a reliable third party.

RAM

The 800 G5 SFF has four 288-pin DIMM slots, all of them user-accessible, with nothing soldered. It takes standard desktop UDIMMs (not the small laptop-style SO-DIMMs used by the Mini and All-in-One models).

What fits: DDR4-2666 (PC4-21300) unbuffered, non-ECC modules at 1.2 V, CL19. The maximum is 32 GB per module, giving 128 GB total with four modules. Registered (RDIMM), ECC and x4 SDRAM modules are not supported, so shop for plain non-ECC UDIMMs.

Speed: 2666 MT/s is the ceiling. The BIOS offers no XMP, so a faster-rated kit (say DDR4-3200) will simply run at 2666 MT/s - don't pay extra for speed you can't use. HP says the machine runs at maximum performance mode only when the two DIMMs are identical part numbers, and the actual rate is set by the slowest module in the system. One older HP guide quotes DDR4-2400 for this platform; the G5 SFF service guide is explicit that the spec is DDR4-2666 CL19, and that's what we'd buy for.

The slots run two per channel (DIMM1 and DIMM2 are Channel B, DIMM3 and DIMM4 are Channel A). Fill both channels equally for dual-channel, which HP notes matters for graphics performance; with unequal channels the machine falls back to flex mode, and HP says to put the extra module in Channel A. Filling a single channel only gives you single-channel performance.

Buying tip: a matched pair or matched set of 2666 MHz non-ECC UDIMMs is the sweet spot. If you're buying two modules, get identical part numbers to keep HP's max performance mode.

Buying tips

• DDR4-2666, non-ECC, unbuffered desktop UDIMM - nothing faster is worth paying for
• 32 GB per module is the maximum; 4 x 32 GB = 128 GB
• Buy identical part numbers for two-module kits
• Avoid ECC, RDIMM and x4 modules - they aren't supported

Storage

There are three kinds of storage inside the 800 G5 SFF: two M.2 slots for NVMe SSDs, two 3.5-inch SATA bays and one 2.5-inch SATA bay. There is also a slim 9 mm SATA optical bay and, on some units, an SD card reader.

M.2 slots (2): two PCIe x4 M.2 combo slots that take 2230 or 2280-length NVMe SSDs. HP's largest factory option is 2 TB per slot (TLC), which is the biggest figure documented rather than a proven hard limit. Two things to watch. First, SATA M.2 drives (the B+M key type) are not listed as supported - buy NVMe only. Second, the 2230 form factor needs the correct standoff and screw. There is a third M.2 2230 slot on the board, but it is for WLAN cards only (PCIe x1, and HP's BIOS whitelist applies), so don't expect to put a drive in it.

3.5-inch SATA bays (2): HP's service guide lists two 3.5-inch internal bays, while retail listings describe them as 2.5/3.5-inch combo bays - if you plan to fit 2.5-inch drives here, check what adapters or caddies come with your unit. The factory maximum is a 2 TB 7200 rpm SATA HDD; no absolute capacity limit is documented. Note that HP's Storage Drivelock feature does not work with self-encrypting drives or Optane H10 storage.

2.5-inch SATA bay (1): takes SATA HDDs, SSDs and self-encrypting drives; factory options topped out at a 2 TB HDD or 512 GB SSD, with no documented hard limit and no published thickness limit. The important caveat: in factory configurations this bay is mutually exclusive with a second M.2 drive, a discrete graphics card and 95 W CPUs. If you plan to add a graphics card or a fast 95 W processor, build your storage around the M.2 slots and the 3.5-inch bays instead.

One other practical note from the chassis: adding a discrete graphics card takes the 2.5-inch bay out of play, and the small case and power supply limit how long and how power-hungry a graphics card can be. Expansion slots take low-profile cards only.

Buying tip: start with an NVMe M.2 2280 SSD in one of the free combo slots - it's the simplest, fastest upgrade - and use the 3.5-inch bays for bulk storage. Check inside the case first, since one M.2 slot is usually occupied by the factory boot drive and the bays may or may not come with caddies.

Buying tips

• M.2 storage: NVMe PCIe SSDs in 2280 or 2230 - SATA M.2 will not work
• 2 TB per M.2 slot is the largest documented factory figure, not a proven limit
• 2.5-inch drives in the 3.5-inch bays may need an adapter or caddy
• Skip the 2.5-inch bay if you want a GPU or a 95 W CPU - plan around M.2 and 3.5-inch drives

CPU

The processor is socketed and replaceable: an LGA1151v2 socket on HP's Q370 board, and HP's G5 specifications list 9th-generation Intel Coffee Lake Refresh processors only - Core i3, i5, i7 and i9 plus Pentium and Celeron.

8th-generation parts physically fit the same socket and chipset, but they are not HP-listed for the G5, so treat them as unsupported and BIOS-dependent rather than guaranteed. Stick to the 9th-gen parts HP lists if you want a smooth upgrade.

Power: 65 W is the mainstream tier, and 95 W K-series processors are supported in the SFF. Before you pick a 95 W chip, remember the storage trade-off above - a 95 W processor rules out the 2.5-inch bay in factory configurations - and check that the cooling and power supply in your unit suit it. Also note that a K-series chip buys you nothing beyond its stock clocks here: the HP BIOS has no XMP or overclocking controls.

Buying tip: check HP's G5 QuickSpecs list of supported processors before ordering, and compare the price of a used 65 W Core i5 or i7 against the 95 W parts. Make sure your BIOS is up to date before installing a newer stepping - see the steps below.

Also worth knowing if you're opening the case anyway: the SFF has two PCIe 3.0 x1 slots, one PCIe 3.0 x16 slot at full x16 bandwidth and a second x16-length slot wired at x4. All of them take low-profile cards only.

Buying tips

• 9th-gen Intel only for guaranteed support (Core i3/i5/i7/i9, Pentium/Celeron)
• 65 W mainstream; 95 W K-series fits the SFF but costs you the 2.5-inch bay
• No overclocking or XMP - don't pay extra for a K chip expecting more
• Low-profile PCIe cards only

How to upgrade

Before you start

• Back up anything you care about - especially before touching storage.
• Check HP's support site for BIOS and firmware updates and install any needed updates before adding the new part.
• Power the PC off, switch it off at the wall and unplug the power cable and all peripherals.
• Ground yourself (touch the metal chassis or use an antistatic strap) before handling components.
• Open the case. For the exact release mechanism, screws and cable routing for the 800 G5 SFF, follow the illustrated steps in HP's Maintenance and Service Guide for this model.
• Install the part, close the case, reconnect everything and power on.
• Check that the BIOS/Setup (and your operating system) sees the new part at the expected size and speed.

Steps

1. 1. Back up and update
   Back up your data first, and install any available BIOS and firmware updates from HP before you open the case. Note down your current BIOS version and memory/drive configuration so you can compare afterwards.
2. 2. Power down
   Shut down fully, switch off at the wall, unplug the power lead and all cables, and move to a clear, well-lit workspace.
3. 3. Open the case and ground yourself
   Touch bare metal on the chassis to discharge static, then open the case. The 800 G5 SFF service guide shows the exact procedure for this chassis - follow it rather than pulling at panels.
4. 4. Install the part
   Seat memory modules firmly until the side clips lock, screw M.2 drives down with the correct standoff (2230 and 2280 use different positions), and mount SATA drives in their caddies with the cables connected the right way round. For a CPU, lift the socket lever, align the marked corners, drop the chip in without forcing it, and refit the cooler.
5. 5. Close up and check
   Refit the cover, reconnect power and peripherals, then start the PC and enter BIOS/Setup. Confirm the new RAM total and speed, that every drive is detected, and that a new processor is identified correctly. Finally check the part in your operating system.

Good to know

• HP's documents cover the whole 800 G5 family; the Mini and All-in-One versions use SO-DIMMs and max out at 64 GB, so check which chassis you own.
• One HP maintenance guide quotes DDR4-2400 for this platform; the G5 SFF guide specifies DDR4-2666 CL19.
• 2 TB per drive is the largest factory option - no absolute capacity limit is documented.
• The three bay types are described slightly differently in HP's service guide (2x 3.5-inch) and retail listings (2.5/3.5-inch combo); verify what caddies your unit includes.

Frequently asked questions

How much RAM can the HP EliteDesk 800 G5 SFF take?

128 GB total, using four 32 GB DDR4-2666 non-ECC desktop UDIMMs. All four slots are user-accessible and nothing is soldered. Note that the Mini and All-in-One versions of the 800 G5 use laptop memory and top out at 64 GB.

Can I overclock the RAM or CPU?

No. The HP BIOS exposes no XMP or overclocking controls, so memory runs at a maximum of 2666 MT/s and even a K-series processor runs at stock clocks.

Does the 800 G5 SFF support SATA M.2 SSDs?

No. The two storage M.2 slots are PCIe x4 NVMe only; SATA (B+M key) M.2 drives are not listed as supported. Both slots accept 2230 or 2280 modules.

Which CPUs are supported?

9th-generation Intel Coffee Lake Refresh processors (Core i3/i5/i7/i9 plus Pentium/Celeron) on the LGA1151v2 socket, up to 95 W in the SFF. 8th-generation chips fit physically but aren't listed by HP for the G5, so treat them as unsupported.

Can I add a graphics card?

Yes, but only low-profile cards, and the chassis and power supply limit card length and power draw. A discrete graphics card also rules out the 2.5-inch drive bay, so plan storage around the M.2 slots and 3.5-inch bays.

How many SSDs can I install?

Up to two NVMe M.2 SSDs (up to 2 TB each as factory-configured), plus SATA drives in the 3.5-inch and 2.5-inch bays. The 2.5-inch bay is not available alongside a second M.2 drive, a discrete GPU or a 95 W CPU.

Official documents and references

• PDF HP EliteDesk 800 G5 SFF Maintenance and Service Guide (PDF)
  HP's step-by-step disassembly and upgrade instructions for this chassis.
• PDF HP EliteDesk 800 G5 QuickSpecs (PDF)
  Official configuration limits: supported processors, memory sizes and storage options across the G5 family.
• PDF HP EliteDesk 800 G5 SFF datasheet (PDF)
  Small Form Factor specific slots, bays and expansion details.
• HP support forum: Upgrading HP EliteDesk 800 G5 SFF
  Owner experiences, including the absence of XMP/overclocking in the BIOS.