Lenovo ThinkCentre M900 Tower upgrade guide: RAM, SSD and CPU

Lifecycle and support

Standard support ended on November 2018 (estimate).

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

RAM: 4 slots, up to 64 GB

The M900 Tower has four 288-pin DIMM sockets (DIMM1–DIMM4 on the system board), dual-channel capable, and nothing is soldered, so all four are yours to use. It takes DDR4 UDIMM, unbuffered, non-ECC, 1.2 V memory at DDR4-2133.

Per-module limit: 16 GB. Total limit: 64 GB, which requires four 16 GB modules; with four 8 GB sticks you get 32 GB. Any mix of 4/8/16 GB modules works.

What won't fit: SO-DIMM (laptop memory), DDR3, ECC and registered/server modules. These either won't seat or won't POST.

Faster DDR4 (2400–3200 MT/s) is fine to buy — it simply clocks down to 2133 MT/s (the optimal speed for the installed CPU), so there is no point paying a premium for speed you won't see.

Buying tip: shop by price per module, not speed rating; four cheap DDR4-2400 or 2666 UDIMMs give you the same real-world performance as DDR4-2133 sticks here.

Buying tips

• Unbuffered non-ECC DDR4 UDIMM only — check the label says UDIMM, not SO-DIMM
• To reach 64 GB you need 4x 16 GB; to reach 32 GB, 4x 8 GB
• Cheaper, faster DDR4 is fine — it runs at 2133 MT/s anyway

Storage: SATA bays plus one M.2 NVMe slot

You get four onboard SATA 6 Gb/s ports feeding tool-less internal 3.5-inch/2.5-inch bays and the 5.25-inch optical bay (which you can repurpose for a drive with a caddy). Supported drives include SATA 2.5-inch and 3.5-inch HDDs, 2.5-inch SATA SSDs and hybrid SSHDs.

Port budget: there are four SATA connectors in total, and the optional rear eSATA port uses one of them — add eSATA and you drop to three internal drives. RAID 0 and RAID 1 (Intel RST) are supported; RAID 5/10 is not.

The system board also has one M.2 slot for an NVMe SSD over PCIe 3.0 x4 (32 Gb/s). One caveat: the available Lenovo documentation doesn't state which M.2 lengths are supported — 2242/2280 are typical for this platform, but that is not confirmed, so check the full PSREF spec sheet or the Hardware Maintenance Manual before ordering a drive. Also, not every M.2 part is bootable on every BIOS revision; if you plan to boot from NVMe, a BIOS/firmware update may be needed first.

One trap to avoid: the internal connector described in the user guide as an 'M.2 card slot' is for Lenovo's optional M.2-to-legacy-PCI adapter card — it is not a spare PCI slot and not a second M.2 storage socket.

Buying tip: a 2.5-inch SATA SSD is the simplest, most compatible upgrade; go NVMe only if you've confirmed the M.2 drive length fits.

Buying tips

• SATA SSD or HDD goes in the tool-less bays; the 5.25-inch bay works with a caddy
• Adding eSATA costs you one internal SATA port
• Verify M.2 drive length (2242/2280 not documented) before buying an NVMe SSD

CPU: LGA1151, 6th-gen Skylake only

The CPU is socketed (LGA1151) on Intel's Q170 platform, so it is replaceable — but Lenovo's supported list stops at 6th-gen 'Skylake' chips: Celeron, Pentium, and Core i3/i5/i7 parts, with a 65 W maximum TDP.

What fits: 65 W Skylake desktop CPUs such as the Core i5-6500/i5-6600 or the top listed part, the Core i7-6700.

What doesn't, officially: 7th-gen 'Kaby Lake' CPUs and 91 W 'K' parts. They share the LGA1151 socket, but Lenovo doesn't support them here and they aren't guaranteed to work — don't buy one expecting an upgrade path. Lenovo's documents confirm the socket and generation list; the point is simply that socket compatibility is not the same as support.

If vPro matters to you, it's present only on the Core i5-6500/i5-6600 and Core i7-6700.

Buying tip: the biggest real-world jump here is usually going from a Celeron/Pentium or Core i3 to a Core i5 or i7-6700 — and if your machine already has an i5, an i7-6700 is the only official step up, so weigh the gain against the price.

Buying tips

• 6th-gen Skylake, 65 W or less, LGA1151 — that's the safe envelope
• Avoid 7th-gen and 91 W 'K' CPUs despite the shared socket
• Need vPro? Only i5-6500/i5-6600 and i7-6700 have it

How to upgrade

Before you start

• Back up anything you care about before opening the case.
• Shut the machine down fully and unplug the power cable and any peripherals.
• Ground yourself — touch the metal chassis before handling parts, and hold modules and cards by their edges.
• Open the case (the exact latch/screw arrangement is in the owner's manual; the drives themselves are tool-less).
• Install the part, taking care with CPU socket pins and RAM alignment — the notches only let DDR4 seat one way.
• Close the case, reconnect power and start the machine.
• Check that the BIOS/firmware sees the new part, and for an M.2 NVMe boot drive, make sure the firmware is updated and the drive is set as boot device if needed.

Steps

1. Installing RAM
   Use the four DIMM sockets (DIMM1–DIMM4). Seat each module firmly at both ends until the clips click. Nothing is soldered, so all four slots are available. Check the BIOS reports the new total after reboot; the user guide shows the slot layout and page 32 area details the DIMM positions.
2. Installing a SATA or M.2 drive
   For 2.5-inch/3.5-inch drives, use the tool-less bays or the 5.25-inch bay with a caddy, and connect a SATA 6 Gb/s cable to a free port (remember the eSATA option occupies one). For an NVMe SSD, use the single M.2 slot after confirming the drive's length against Lenovo's documentation. If you want to boot from NVMe, check for a BIOS/firmware update first. RAID 0/1 only if you plan a two-drive array.
3. Replacing the CPU
   The processor sits under the heatsink on the LGA1151 socket with its own fan connector. Only 6th-gen Skylake parts up to 65 W are supported. Follow the owner's manual for heatsink removal and re-fitting, and apply fresh thermal compound if you separate the cooler from the chip. Confirm the new CPU model in the BIOS afterwards.

Good to know

• Bay-by-bay details (exact 3.5-inch bay count and 2.5-inch thickness limits) are in the full PSREF table; confirm in the PSREF PDF or Lenovo's component page before planning a multi-drive build.
• M.2 drive length support is not documented in the available Lenovo sources — treat 2242/2280 as unconfirmed and check before buying.
• Don't assume 7th-gen CPU support just because LGA1151 chips physically fit — Lenovo's list ends at 6th-gen Skylake, 65 W.

Frequently asked questions

How much RAM can the Lenovo ThinkCentre M900 Tower take?

64 GB maximum, in four DDR4-2133 non-ECC UDIMM slots (4x 16 GB). A 16 GB module is the largest supported stick, and none of the memory is soldered.

Can I use laptop (SO-DIMM) or ECC memory in the M900 Tower?

No. The slots take 288-pin DDR4 UDIMM, unbuffered, non-ECC, 1.2 V only. SO-DIMM, DDR3, ECC and registered memory won't fit or won't POST.

Does the M900 Tower support an M.2 NVMe SSD?

Yes — one M.2 slot, PCIe 3.0 x4 NVMe (32 Gb/s). The supported M.2 lengths aren't stated in the available Lenovo documents (2242/2280 are typical for this platform), so verify against the PSREF sheet or Hardware Maintenance Manual before buying. Booting from NVMe may need a BIOS update.

Which CPUs fit the ThinkCentre M900 Tower?

6th-gen Intel Skylake processors on LGA1151, up to 65 W — Celeron, Pentium, Core i3/i5/i7, topping out at the Core i7-6700. 7th-gen Kaby Lake and 91 W 'K' chips are not officially supported even though the socket is the same.

How many drives can I install?

Up to four SATA drives across the tool-less 2.5/3.5-inch bays and the 5.25-inch optical bay, plus one M.2 NVMe SSD. The optional rear eSATA port uses one of the four SATA connectors, leaving three internal. RAID 0/1 only.

Is the M900 Tower the same inside as the M900 SFF?

No. They share the name but differ in bays, expansion slots and media readers (29-in-1 on the Tower vs 9-in-1 on the SFF). Confirm your type number (10FM/10FL, also 10FR/10FS) before ordering parts.

Official documents and references

• PDF Lenovo PSREF — ThinkCentre M900 Tower specification sheet (PDF)
  Official platform specs: memory, SATA/eSATA, RAID and storage options
• PDF Lenovo M800/M900 Tower User Guide (PDF)
  System board layout (DIMM slots, LGA1151 socket, drive bays) and disassembly procedures
• Lenovo PSREF — ThinkCentre M900 Tower product page
  Supported CPU list and platform overview
• Lenovo support — ThinkCentre M900 components (types 10FL/10FM/10FR/10FS)
  Model identification and component information for the Tower types
• Lenovo support — Detailed specifications and overview for ThinkCentre M900
  Chipset, CPU support and detailed specs
• Kingston memory configurator — Lenovo ThinkCentre M900 (SFF/Tower)
  Confirms 4 sockets, 64 GB max, module type, and that faster DDR4 clocks down