Dell Precision Tower 3420 Upgrade Guide: RAM, SSD and CPU

Lifecycle and support

No longer sold new. The manufacturer hasn't published an end-of-support date.

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

RAM: up to 64 GB of DDR4 UDIMM

The 3420 has four DIMM slots that take desktop DDR4 UDIMMs. Dell lists module sizes of 4, 8 and 16 GB, a 4 GB minimum, and a maximum of 64 GB (4 x 16 GB). SO-DIMM laptop memory and registered (RDIMM) server memory do not fit or are not supported. No memory is soldered to the board.

On speed, Dell's documents disagree. The owner's manual lists 2133 MHz, while Dell's combined 3620/3420 tech guide also lists 2400 MHz non-ECC memory. Per that guide, 2400 MHz only works with a 7th gen Intel CPU. With a 6th gen Core or Xeon E3-1200 v5 processor, 2400 MHz modules run at 2133 MHz.

ECC memory works only with a Xeon processor, and ECC and non-ECC modules cannot be mixed. Core i3, i5 and i7 chips take non-ECC memory only. Dell recommends filling both memory channels for best performance, so install modules in matched pairs.

Buying tips

• Buy DDR4 desktop UDIMMs only, not SO-DIMM or RDIMM.
• Choose non-ECC memory unless you have a Xeon CPU installed.
• Buy matched pairs so both channels are populated.
• 2400 MHz modules are fine, but expect 2133 MHz unless you have a 7th gen CPU.
• Stick to 16 GB or smaller modules; that is the largest size Dell lists.

Storage: one M.2 NVMe slot plus SATA drives

The motherboard has one M.2 2280 slot (22 x 80 mm) running PCIe Gen3 x4, and Dell lists up to 1 TB. The BIOS shows it as M.2 PCIe SSD-0. The board labels the slot 'SATA or PCIe SSD Slot', but Dell's documents don't confirm that SATA M.2 drives work, so buy an NVMe drive.

For more NVMe capacity, Dell offers its Precision Ultra-Speed Drive, a PCIe x8 add-in card with active cooling that holds one more SSD of up to 1 TB. It takes up one of the two half-height PCIe slots (one x16 Gen3, one x4 Gen3).

SATA drives go in the single internal 3.5 inch bay, which holds either one 3.5 inch drive or two 2.5 inch drives. The board has three SATA connectors. Dell lists 3.5 inch HDDs up to 4 TB at 5400 RPM or 2 TB at 7200 RPM, 2.5 inch 7200 RPM HDDs up to 1 TB, and 2.5 inch SSDs up to 512 GB. Larger 2.5 inch SSDs may well work, but Dell doesn't list them. Fitting 2.5 inch drives needs a bracket or adapter, and drive thickness limits aren't given.

Dell's tech guide covers both the 3620 and 3420, and the two have different bay counts. Check the 3420 column or your own machine before buying a caddy or bracket. An optional internal SD card reader also exists.

Buying tips

• Buy an M.2 2280 NVMe SSD, not a SATA M.2 drive.
• 1 TB is the largest size Dell lists for the M.2 slot.
• For a second NVMe drive you need Dell's Ultra-Speed Drive card and a free PCIe slot.
• A 2.5 inch SSD over 512 GB is unlisted by Dell, so treat it as untested.
• Confirm the bay layout in your machine before buying a drive bracket.

CPU: 6th and 7th gen only, up to 80 W

The processor is socketed and removable, and there is a single socket. Dell's documents don't spell out the socket name in the manual text, but the listed CPUs use LGA1151. Dell lists 7th gen Core i7 and i5, 6th gen Core i7, i5 and i3, and the Xeon E3-1200 v5 family, on the Intel C236 chipset. Dell's guide names these specific models: Core i7-6700, i5-6600, i5-6500 and i3-6100, and Xeon E3-1220, E3-1225, E3-1240, E3-1245 and E3-1270. We could not find a model list for 7th gen chips. Not every part was offered at the factory, and availability varied by region.

The highest rating listed is 80 W (the Xeon E3 v5 parts; the Core parts are 65 W). Dell documents no cooling limit beyond its supported list, so treat 80 W as the ceiling. 8th gen and newer Core CPUs, and Xeon E3-1200 v6, are not listed, so don't assume they work. The system uses a 180 W or 240 W power supply.

The Xeon E3-1220, E3-1240, E3-1270 and the Core i3-6100 have no integrated graphics and need a discrete graphics card. The E3-1225, E3-1245 and the Core i5/i7 parts list Intel HD 530 graphics.

If you are moving a 6th gen system to a 7th gen CPU, update the BIOS first. Dell lists 7th gen as supported but doesn't document a minimum BIOS version, so check the release notes on Dell's support page. 7th gen CPUs are listed with Windows 10, Red Hat Enterprise Linux 7.3 and Ubuntu 16.04; Windows 7 and 8.1 are listed only with 6th gen.

Buying tips

• Stick to LGA1151 6th or 7th gen Core, or Xeon E3-1200 v5.
• Don't buy 8th gen or newer chips; they are not supported.
• Skip the i3-6100 and Xeon E3-1220, E3-1240 and E3-1270 unless you have a graphics card.
• Pick a Xeon only if you want ECC memory.
• Update the BIOS before fitting a 7th gen CPU.

How to upgrade

Before you start

• Back up your files before opening the machine.
• Have your Windows or other OS login details to hand in case you need to reinstall.
• Check your current BIOS version, and update it first if you plan to fit a 7th gen CPU.
• If you update the BIOS, Dell advises not jumping more than three revisions at once. For example, to go from 1.0 to 7.0, install 4.0 first, then 7.0.
• Work on a clean, well-lit surface with a small screwdriver ready.
• Keep the owner's manual for the exact disassembly steps for your chassis.

Steps

1. Back up and update
   Back up your data. If you are fitting a 7th gen CPU, update the BIOS before you swap the processor.
2. Power off and unplug
   Shut the computer down fully, unplug the power cable and any other cables, and hold the power button for a few seconds to drain leftover charge.
3. Ground yourself
   Touch bare metal on the case or wear an anti-static wrist strap before touching any components. Handle memory, SSDs and CPUs by their edges.
4. Open the case
   Remove the side cover following the owner's manual. For a CPU swap, Dell's manual also has you remove the front bezel, the hard drive and the heat sink to reach the processor.
5. Install the part
   For memory, seat the modules fully in the DIMM slots, filling both channels. For an M.2 SSD, fit it into the single M.2 slot. For a SATA drive, use the internal bay and a bracket if you are fitting 2.5 inch drives. For a CPU, release the socket lever, lift the shield and lift out the old chip. Fit the new one with the pin-1 triangle and the notches aligned to the socket keys, then close the shield and lock the lever. Refit the heat sink as the manual describes.
6. Close up and reconnect
   Refit the drive, bezel and cover, then reconnect the cables.
7. Check the BIOS
   Power on and enter the BIOS setup. Confirm the new memory total, CPU or drive is listed. An NVMe drive in the motherboard slot should appear as M.2 PCIe SSD-0. Then install or boot your operating system.

Good to know

• Dell's documents don't give a minimum BIOS version for 7th gen CPUs, so check the BIOS release notes on Dell's support page before swapping.
• Dell doesn't list 7th gen CPU models by name, only that 7th gen Core i7 and i5 are supported.
• Dell's tech guide is shared with the 3620, so some rows (bay counts, optical bays, extra expansion slots) may not apply to the 3420. Check against your own machine.
• Dell doesn't confirm whether the M.2 slot accepts SATA M.2 drives, despite the board label.
• Drive thickness limits for the 2.5 inch and 3.5 inch bays are not documented.
• 2.5 inch SSDs above 512 GB are not listed by Dell and may or may not work.
• No cooling limit beyond the 80 W listed CPUs is documented, so unlisted higher-power CPUs are not validated.

Frequently asked questions

How much RAM can the Dell Precision Tower 3420 take?

Up to 64 GB, using four 16 GB DDR4 UDIMMs. The minimum is 4 GB, and module sizes are 4, 8 and 16 GB.

What speed of RAM does the 3420 support?

Dell's documents disagree. The owner's manual lists 2133 MHz, while Dell's tech guide also lists 2400 MHz, which works only with a 7th gen Intel CPU. With 6th gen chips, 2400 MHz memory runs at 2133 MHz.

Does the Precision Tower 3420 support ECC memory?

Yes, ECC UDIMMs are listed, but only with a Xeon processor. ECC and non-ECC modules can't be mixed, and Core i3, i5 and i7 chips take non-ECC only.

Does the 3420 support NVMe SSDs?

Yes. There is one M.2 2280 slot running PCIe Gen3 x4, with Dell listing up to 1 TB. A second NVMe SSD is possible with Dell's Precision Ultra-Speed Drive card, which uses a PCIe slot. Dell's documents don't confirm SATA M.2 drives.

What is the best CPU I can fit in a Precision Tower 3420?

The socket is LGA1151 and Dell lists 6th and 7th gen Core and Xeon E3-1200 v5 chips, up to 80 W. 8th gen and newer Core CPUs aren't supported. Update the BIOS before fitting a 7th gen CPU.

Can I fit a larger 2.5 inch SSD than 512 GB?

Dell only lists 2.5 inch SSDs up to 512 GB. Larger drives may work, but that isn't confirmed. The single internal bay holds one 3.5 inch drive or two 2.5 inch drives, and 2.5 inch drives need a bracket or adapter.

Official documents and references

• PDF Dell Precision Tower 3420 spec sheet
  CPU options, memory, storage and PCIe slot summary
• PDF Dell Precision Tower 3420 owner's manual (PDF)
  Step-by-step removal and installation procedures
• Precision 3420 specifications
  Memory, drive capacity and power supply details
• PDF Dell Precision 3620/3420 tech guide
  Memory speeds and ECC rules (shared with the 3620)
• Precision 3420 system board components
  Locations of the CPU socket, M.2 slot and SATA ports
• Precision 3420 system setup options
  How the BIOS lists your drives
• Updating the BIOS (Precision 3420)
  Dell's BIOS update procedure and revision advice
• Precision 3420 BIOS download
  Latest BIOS and release information