Dell PowerEdge R640 vs R740: NVMe Bays, Slots and Buying
The Dell PowerEdge R640 is the 1U machine in the R740 generation, and it is one of the more interesting 1U servers because of how much fast storage it can carry. This covers what it does well and where 1U still limits you.
What is the Dell PowerEdge R640?
A dual-socket 1U rack server on socket LGA 3647, supporting Intel Xeon Scalable processors, with DDR4 memory across 24 DIMM slots and iDRAC9 remote management.
Same platform as the R740; the chassis height is the difference.
R640 vs R740: which should I buy?
Four differences, all following from 1U against 2U.
Drive bays. The R640 takes fewer — commonly up to 10 small form factor bays, against considerably more on the R740. If bulk capacity lives in the server, the R740 is the answer.
Expansion slots. Fewer, and low-profile only. A full-height card does not fit, and a card supplied with only a full-height bracket needs the low-profile one sourced separately — our PCIe guide covers this.
Accelerator support. The R740 handles GPUs far more readily. A 1U chassis constrains both physical space and cooling, so accelerator options are limited — our accelerator guide covers why a passively cooled card depends entirely on chassis airflow.
Rack density. Twice the machines per rack, which is the point.
Short version: 1U for density and fast local storage, 2U for capacity and cards.
R640 NVMe support: how many drives?
The specification that makes this machine interesting.
Some R640 configurations support all-NVMe front bays, letting a 1U machine carry a substantial amount of very fast local storage without consuming expansion slots.
Three things to confirm before assuming yours does.
NVMe support is per-bay, not per-chassis. A bay that physically accepts an NVMe drive may have no PCIe lanes routed to it — lane routing is a physical wiring decision made when the chassis was configured, as our backplanes guide covers.
NVMe bypasses the RAID controller entirely. Drives connect over PCIe and present directly to the system, so there is no controller-level redundancy — protection comes from software or the storage layer. Our NVMe guide covers the implications.
Lanes are shared with expansion slots. Populating NVMe bays consumes lanes from the same budget, which is a real constraint in a chassis that has few slots to begin with.
Where this fits well: databases, virtualisation hosts and analytics needing fast local storage in minimal rack space. Where it does not: anything needing bulk capacity, since bay count is small regardless of speed.
R640 processor and memory support
Intel Xeon Scalable across Bronze, Silver, Gold and Platinum tiers.
The point worth understanding: the tier is not just a speed ranking. It sets your maximum supported memory speed and how many sockets the processor can work in, so a lower tier caps your memory speed before you buy a module — our Xeon Silver guide covers what each tier determines.
Memory is 24 DIMM slots of DDR4 registered ECC, twelve per processor. Single-processor machines populate twelve only, channels must be filled evenly, and speed can drop as slots fill — our memory guide covers the rules.
One 1U constraint: high-power processors are harder to cool, so check what your specific configuration supports rather than assuming the full processor range is available. Heatsinks are 1U-specific parts, and a second socket frequently requires additional fans.
Do I need iDRAC9 Enterprise on an R640?
Worth settling before purchase.
Basic iDRAC gives health monitoring and hardware inventory. Remote console and virtual media generally require the Enterprise licence — exactly what you need when a machine will not boot and nobody is on site.
This matters more on 1U machines because they are deployed in numbers at colocation and remote sites, precisely so nobody has to attend them. Without remote console, that assumption fails the first time one will not boot — our out-of-band guide covers why that access is what actually resolves an incident.
Check whether a licence is included on used units, since it does not always transfer.
What should I check on a used R640?
Which bays support NVMe, if that is why you are buying it. Rails, which stay in the rack. Drive carriers for empty bays, generation-matched. Risers — with few in 1U, a missing one removes a large share of your expansion capability. Low-profile brackets for cards. The PERC cache battery, without which write performance collapses with no error reported — our PERC guide covers this. And the iDRAC licence.
Note that if you are running all-NVMe, the PERC cache question does not apply to those drives — they bypass the controller. It still applies to any SAS or SATA drives in the machine.
Frequently asked questions
What is the difference between R640 and R740?
The R640 is 1U and the R740 is 2U on the same platform. The R640 takes fewer drive bays, fewer and low-profile-only expansion slots, and is far more limited on accelerators. Choose 1U for density and fast local storage, 2U for capacity and cards.
Does the R640 support all-NVMe drives?
Some configurations do, and it is what makes the machine interesting. But support is per-bay rather than per-chassis — a bay may physically accept a drive with no PCIe lanes routed to it, so confirm which bays are wired for it.
Do NVMe drives use the PERC controller?
No. They connect over PCIe and present directly to the system, bypassing the RAID controller entirely. That means no controller-level redundancy — protection has to come from software or the storage layer.
Can I fit a GPU in an R640?
Options are limited. A 1U chassis constrains both physical space and cooling, and passively cooled accelerators depend entirely on chassis airflow. If GPUs matter, the R740 is the sensible starting point rather than fighting a 1U chassis.
Do I need iDRAC9 Enterprise on a used R640?
For remote console and virtual media, yes — and it matters more here because 1U machines are deployed in numbers at remote sites precisely so nobody has to attend them. Check whether a licence is included, since it does not always transfer.
Does adding NVMe drives limit my expansion slots?
It can. NVMe bays consume PCIe lanes from the same budget as expansion slots, which is a real constraint in a 1U chassis that has few slots to begin with.
Tell us whether NVMe matters and how many drives you need, and we will confirm which R640 configuration actually supports it.
