Dell PowerEdge R640: A 1U Built for NVMe

The PowerEdge R640 is Dell's 14th-generation two-socket 1U server, and it is usually where people land when they want a lot of flash in a single rack unit without moving to a 2U chassis. Two LGA 3647 sockets, 24 DDR4 DIMM slots, and up to ten 2.5-inch front bays, several of which can be wired for NVMe, is a dense combination for 1.75 inches of rack height.

Processors, memory, and the population rules that matter

Both sockets accept Intel Xeon Scalable processors, first generation (Skylake-SP) and second generation (Cascade Lake), from low-core-count Bronze parts through 28-core Platinum SKUs. TDP support reaches 205 W, but the top-wattage parts carry heatsink and ambient-temperature requirements that a 1U chassis takes seriously. Dell's threshold for the high-performance heatsink on this generation is above 150 W, so from that point up you should confirm that the correct heatsink and the matching fan complement are actually installed.

Memory is six channels per socket, two DIMMs per channel: 12 slots per CPU, 24 in total, up to 3 TB with 128 GB LRDIMMs. That 3 TB headline deserves a footnote. Twelve 128 GB modules is 1.5 TB per socket, which is above the 768 GB per socket that standard first-generation parts address and above the 1 TB per socket that standard second-generation parts address, so the full 3 TB requires M-suffix processors. The practical rule is to populate in multiples of six per CPU. Twelve identical DIMMs, six per socket, gives full bandwidth across both CPUs; eight per socket boots fine but leaves an unbalanced channel layout and measurable bandwidth on the table. First-generation Xeon Scalable tops out at 2,666 MT/s. Second-generation parts support 2,933 MT/s, but generally only at one DIMM per channel; fill the second DIMM per channel and the bus typically drops back to 2,666.

One firmware detail worth checking before you order CPUs: a system still running first-generation-era BIOS needs an update before it will POST with Cascade Lake. It is a short job through iDRAC, but it is not optional.

Why the NVMe backplane changes the machine

SAS and SATA drives in an R640 hang off a PERC controller such as the H330, H730P, H740P, or an HBA330 running in pass-through. NVMe drives do not. U.2 NVMe bays connect to CPU PCIe lanes through extender cards, so each drive gets its own PCIe 3.0 x4 path instead of sharing a controller's queues. Three consequences follow:

• There is no hardware RAID across the NVMe bays. PERC controllers that can build RAID sets from NVMe drives arrived with the following server generation, not this one, so redundancy here comes from the OS or hypervisor layer: mdraid, ZFS, Storage Spaces, vSAN, or Ceph.
• NVMe bays consume real CPU lanes, so a heavily populated NVMe configuration expects both sockets filled.
• Backplanes are not interchangeable. Whether a subset of the bays or the full ten are NVMe-capable is decided by the backplane and cabling physically installed in that chassis. Confirm the layout rather than assuming a 10-bay front panel means ten NVMe slots.

For boot, the BOSS-S1 card carries two M.2 SATA modules in RAID 1 on an internal riser and keeps the hypervisor off the front bays entirely. The older IDSDM dual-SD module still turns up in these systems, but VMware has moved away from SD and USB boot media, so BOSS is the more durable choice for a host you intend to keep patching.

Slots, networking, and what the second CPU unlocks

A 1U chassis limits expansion. The R640 offers up to three PCIe 3.0 slots, all low-profile, alongside a dedicated PERC slot and a network daughter card (rNDC) slot that carries the onboard LAN. The rNDC is the easiest way to change network personality: swapping a 4 x 1GbE card for a 2 x 10GbE or 2 x 25GbE daughter card leaves all three PCIe slots free for HBAs or additional NICs.

Slot availability depends on the riser configuration and on the second socket being populated, because some risers are wired to CPU2 and go dark in a single-CPU build. If you are considering a single-processor R640, verify which slots stay live in that configuration before planning cards around them.

R640 or R740 in the same generation

Attribute	PowerEdge R640	PowerEdge R740
Rack height	1U	2U
Sockets / DIMM slots	2 x LGA 3647 / 24	2 x LGA 3647 / 24
Front drive bays	Up to 10 x 2.5" or 4 x 3.5"	Up to 16 x 2.5" or 8 x 3.5"
PCIe 3.0 slots	Up to 3, low-profile	Up to 8 depending on riser config
Double-width GPUs	No	Yes, riser and power dependent
Management	iDRAC9	iDRAC9

If the workload needs accelerators, more than three add-in cards, or more than ten spindles, the 2U R740 is the better starting point. If it needs flash density per rack unit, the R640 is the reason this platform exists.

Management and the details that bite later

iDRAC9 handles out-of-band management. The Express tier covers health, inventory, and power control; virtual console and virtual media, which are the features you actually want when the server sits in a colo, require the Enterprise license. Check the license level in the iDRAC web interface before you plan a remote OS install.

Two more practical notes. A 1U server running 205 W-class CPUs is loud under sustained load, so this is rack-room hardware, not office hardware. And confirm the rail kit matches your rack posts and depth; sliding rails without a cable management arm get old quickly on a server you service often.

Where to go from here

Browse the current Dell PowerEdge R640 systems to see which chassis, backplane, and CPU pairings are on hand, or compare against the R740 if slot count is the deciding factor. When you know the CPU, memory, backplane, and controller combination you want, put it together on Build Your Server and send it over as a quote request; our team will confirm the configuration is valid before anything ships.