Dell PowerEdge T640 Upgrade Guide: RAM and Storage

Lifecycle and support

No longer sold new. Supported until Dec. 31, 2028 (estimate).

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

RAM: registered ECC DDR4 only

The T640 has 24 full-size DIMM slots, 12 per CPU, arranged as 6 channels with 2 DIMMs per channel. It accepts registered ECC DDR4 only, in RDIMM or LRDIMM form. RDIMMs go up to 64 GB per module and LRDIMMs up to 128 GB. The minimum is one 8 GB module, and the maximum is 3 TB (24 x 128 GB LRDIMMs). Dell also supports up to 12 NVDIMM-N modules (16 GB each) alongside RDIMMs.

Speed depends on your CPUs and how many DIMMs you fit. 2933 MT/s needs 2nd-gen Xeon Scalable CPUs, one DIMM per channel and 16, 32 or 64 GB dual-rank RDIMMs. With two DIMMs per channel, 1st-gen CPUs or LRDIMMs, expect 2666 MT/s. All channels run at the speed of the slowest module.

Population rules from Dell: you can't mix RDIMM and LRDIMM (only NVDIMM with RDIMM), you can use at most two different capacities and two different ranks, the largest DIMM goes in slot A1 first, and CPU2's slots mirror CPU1's. For best performance, fill 6 or 12 DIMMs per CPU.

CPU2's 12 slots most likely need a second CPU installed, and Dell says PCIe slots 4 to 8 do. A single-CPU machine therefore gets half the memory slots.

Dell's documents disagree in a few places. The spec sheet and quick reference guide print 2993 MT/s, which looks like a typo for 2933. The technical guide gives system maximums of 1.5 TB for LRDIMMs and 768 GB for RDIMMs in one table, while its summary and the spec sheet say 3 TB. The 3 TB figure matches 24 x 128 GB. The technical guide also lists a Xeon E-2100 ECC UDIMM row, which contradicts the registered-only rule and looks like a documentation error. Don't buy UDIMMs.

Buying tips

• Buy registered ECC DDR4 RDIMMs or LRDIMMs only, never UDIMMs or SO-DIMMs.
• Pick one type, RDIMM or LRDIMM, and stick to it.
• Choose LRDIMMs only if you need modules larger than 64 GB.
• For the full 2933 MT/s, check you have 2nd-gen Xeon Scalable CPUs and plan one DIMM per channel.
• Buy matched sets, ideally 6 or 12 modules per CPU.

Storage: bays are set at the factory

The front bay layout is chosen when the server is built. Dell lists these configurations: 8 x 3.5" SAS/SATA, 8 x 2.5" in 3.5" carriers, 18 x 3.5" SAS/SATA, 16 x 2.5" SAS/SATA, 16 x 2.5" with 8 NVMe, and 32 x 2.5" SAS/SATA. The backplane is also chosen at purchase and probably isn't easy to swap, so check what a used unit has before you buy. 2.5" drives in 3.5" bays need carriers.

SATA and SAS (up to 12 Gbps) HDDs and SSDs are supported. NVMe SSDs only work on the 16 x 2.5" chassis with 8 NVMe bays. Dell lists NVMe SSDs from 800 GB to 6.4 TB, and also offers HHHL PM1725 NVMe add-in card kits. Dell's internal controller options include the PERC H330, H730P, H740P, HBA330 and software RAID S140. Dell's documents don't give 2.5" drive height limits (7 mm versus 15 mm), so check the owner's manual or Dell support before buying thick drives. For total capacity, Dell's spec sheet quotes 288 TB for 3.5" bays while its generation comparison matrix says 216 TB, probably because they assume different drive sizes.

For boot drives, an optional rear BOSS card holds two M.2 SSDs (80 mm or 110 mm) with hardware RAID. Dell lists 120 GB and 240 GB drives. These are not hot-plug. Dell describes them as M.2 SATA or PCIe x1 but doesn't confirm NVMe, and there are no M.2 slots on the motherboard itself. A separate optional rear module takes microSD cards: IDSDM accepts 16, 32 or 64 GB cards, while vFlash is 16 GB only. Don't assume either module is present in a used unit.

Buying tips

• Check the bay count and backplane of the exact unit before buying drives.
• Buy 3.5" carriers if you want to put 2.5" SSDs in 3.5" bays.
• Only buy NVMe drives if the unit is the 16 x 2.5" plus 8 NVMe build.
• Confirm the BOSS card or microSD module is fitted before buying M.2 or microSD cards.
• If you need an M.2 boot drive, look for the 120 GB or 240 GB sizes Dell lists, and don't assume NVMe works.

How to upgrade

Before you start

• Check whether your T640 has one or two CPUs installed; this decides how many DIMM slots and PCIe slots you can use.
• Note your drive bay configuration (8, 16, 18 or 32 bays, and whether it has NVMe bays).
• Back up important data and note any RAID settings.
• Keep the owner's manual handy for exact disassembly instructions.
• Have an anti-static wrist strap and a clear work area ready. The chassis is heavy (about 42 to 50 kg fully built), so get help moving it.

Steps

1. Back up your data
   Make a full backup and note your RAID and BIOS settings before touching hardware.
2. Power off and unplug
   Shut the server down properly, then disconnect all power cables and let it sit for a moment.
3. Ground yourself
   Use an anti-static wrist strap or touch bare metal on the chassis before handling parts. Hold DIMMs and drives by their edges.
4. Open the case
   Open the tower following the owner's manual. Exact removal steps for covers, shrouds and drive carriers are in Dell's manual.
5. Install the part
   For memory, fit the largest DIMM in slot A1 first and mirror the layout on CPU2, using the same type (RDIMM or LRDIMM) throughout. For drives, fit them in carriers where needed and check the bay suits your backplane. BOSS and microSD modules are rear add-ons, and BOSS drives are not hot-plug.
6. Close up and reconnect
   Refit all covers and shrouds, then reconnect power and cables.
7. Check that the system sees it
   Power on and check the BIOS or system setup shows the new memory total or drive. Check your RAID controller sees any new drives, and look for error messages on the front panel or in system logs.

Good to know

• This page doesn't cover CPU upgrades. Dell's documents mention 1st- and 2nd-gen Xeon Scalable CPUs but we don't have a verified list of compatible models, so check Dell's technical guide before buying one.
• Dell's documents disagree on some figures: 2933 vs 2993 MT/s, system maximum memory, and maximum 3.5" storage (288 TB vs 216 TB).
• Dell doesn't document 2.5" drive height limits for the T640.
• Whether the BOSS M.2 slots accept NVMe drives is not confirmed.
• It's likely, but not confirmed, that CPU2's DIMM slots can't be used without a second CPU.
• Dell doesn't appear to publish model-level end-of-sale or end-of-support dates for the T640. Third-party dates exist but are unconfirmed; check support status for your unit's service tag on Dell Support.

Frequently asked questions

How much RAM can the Dell PowerEdge T640 take?

Up to 3 TB, using 24 x 128 GB LRDIMMs. With RDIMMs the module limit is 64 GB. One table in Dell's technical guide shows lower system maximums (1.5 TB for LRDIMMs, 768 GB for RDIMMs), but its summary and the spec sheet say 3 TB.

What type of memory does the T640 use?

Registered ECC DDR4, as RDIMM or LRDIMM. Don't use UDIMMs, and don't mix RDIMM with LRDIMM.

How fast is the memory in a T640?

Up to 2933 MT/s with 2nd-gen Xeon Scalable CPUs and one DIMM per channel. With two per channel, or with 1st-gen CPUs or LRDIMMs, it runs at 2666 MT/s. Some Dell documents print 2993 MT/s, which looks like a typo.

Does the T640 support NVMe drives?

Yes, but only on the factory 16 x 2.5" configuration with 8 NVMe bays. Dell lists NVMe SSDs from 800 GB to 6.4 TB, and also offers HHHL PM1725 NVMe add-in card kits.

Can I add more drive bays to my T640?

Probably not easily. Bay count and backplane are chosen at the factory (8, 16, 18 or 32 bays), so check what your unit has before buying drives.

Can I add a second CPU to unlock more RAM slots?

A second CPU is what enables CPU2's 12 DIMM slots (likely) and PCIe slots 4 to 8. Dell says the system won't boot with only the CPU2 socket populated. This page doesn't list compatible CPU models, so check Dell's technical guide before buying.

Official documents and references

• PDF Dell PowerEdge T640 Technical Guide
  Memory population rules, speeds, PCIe slots and drive support
• PDF Dell PowerEdge T640 Spec Sheet
  Memory, drive and BOSS capacities
• PDF Dell EMC PowerEdge T640 Owner's Manual
  Drive configurations and disassembly procedures
• Dell PowerEdge T640 Installation and Service Manual
  Drive bay configurations and NVDIMM details
• Dell T640 Manual: Flex Bays
  NVMe drive bay and flex bay modules
• PDF Dell T640 / T630 Generation Comparison Matrix
  Capacity figures compared with the previous generation