HP Z420 is the most popular workstation model with the last and best CPUs that use now ridiculously cheap server type of DDR3 memory. Also, the CPUs are now equally cheap. You can add up to 256 GB of memory and CPUs go up to 12 cores.

HP Z420 isn’t the only workstation with LGA2011 v1 socket on the market. Dell has Precision T3600 and Lenovo ThinkStation S30. HP also made dual processor models Z820 and Z620, the latter needs an add-on board for a second CPU, and they weren’t very popular because of the high number of cores already in a single CPU.

The easy pieces

Linus already did this.

Warning – Before you buy a used HP Z420

Z420 is actually a much simpler case than the workstations of the previous generation. With Z600 I had a quite bad luck as I happened to buy one with the first version of the motherboard, which didn’t accept registered ECC memory, only unbuffered ECC memory and max. 4 GB DIMMs when there were only three DIMM slots per CPU. 12 GB of RAM is just too little for a workstation. The limitation was in chipset, so there was no way around it other than getting revision b or c of the motherboard with a newer version of the chipset.

Z420 has only one nasty limitation, which is kind of hardware based. BIOS boot block memory area is write-protected and if it is an older version, there are two versions, Z420 can boot only with older Sandy Bridge or LGA2011 v1 CPUs. That means you are limited to up to 8 CPU cores and there are fewer options than there are v2 CPUs. As soon as newer Ivy Bridge CPUs were available, you could upgrade your Bios Boot Block on at least same generation HP ProLiant servers and upgrade your CPU to v2. And there the demand for server class CPUs were, not on relatively cheap workstations, so no more and fancier v1 CPUs. There is one positive aspect though, used Xeon E5-2690s are sold at only € 12 a piece, shipping included from China (Mar. 2023). Not that v2 CPUs are much more expensive, the fastest 8 core and with the best single thread performance of all CPUs, Xeon E5-2667 v2, was only € 34, all included, from China, the same month.

The BIOS flash ROM chip is soldered directly to the motherboard and there is no dip switch for by-passing the write protection like on ProLiant servers. Can BIOS boot block on Z420 upgraded anyway? Yes, but you might not want to try. On HP community support forum there is a thread z820 e5-2600 v2 ivy bridge upgrade and one reply in particular:

With dual CPU Z820 and back in year 2016 extreme measures were defendable.

There is no easy and reliable way to determine which version of boot block a Z420 has without booting it.

New Boot Block and most recent BIOS.

Old Boot Block, sorry.

Opening the case side cover is very easy and inside you see a manufacturing date stamp and a sticker label:

This was sold with Xeon E5-1620 v2.

On an older Z420 with old Boot Block the sticker is very different.


The serial number can be found on top, bottom, and back of the case and with it, you can get the manufacturing date and presumably if Z420 was sold with v1 or v2 CPU. You go to HP support site, search for Z420 and you should get to a page similar as below:

Click on “Check warranty status”, enter serial number and select country of purchase, click on Warranty details, and you should see either:

Sold with v1 CPU, but with new boot block.


Sold with v2 CPU. Note different name and Product code.

The idea behind a separate, write-protected BIOS Boot Block is nice. You can’t brick Z420, even if BIOS is somehow damaged, Boot Block will be able to flash a new one. HP servers have iLO below BIOS Boot Block and in an emergency you can use iLO to flash Boot Block and there is always a backup copy of the previous BIOS, so they are even harder to brick.

Which CPU?

When they are all so cheap, less than € 40, you just choose core count based on how scalable your workload typically is and pick the fastest one. In the table below, there is one CPU with only 6 cores, the most interesting one, and both uniprocessor CPUs Z420 was originally sold with, for reference. E5-2673 v2 is the only special and rare CPU in the table and at about € 55 currently, it is not worth the price. There are some other rarities and lots of slower ones too, but not worth considering.

CPUGhzTurboCoresCacheCache/coreTDPCPU MarkSingle threadFirst seen
Intel® Xeon® E5-2697 v22,73,512302,5130141241749Q2 2013
Intel® Xeon® E5-2696 v22,53,312302,5143601664Q3 2013
Intel® Xeon® E5-2690 v233,610252,5130134061890Q2 2013
Intel® Xeon® E5-2667 v23,348253,125130122062022Q1 2014
Intel® Xeon® E5-2643 v23,53,86254,16713089711876Q2 2013
Intel Xeon E5-1620 v23,73,94102,513065262015Q3 2013
Intel Xeon E5-2673 v23,348253,125110119191959Q2 2016
Intel® Xeon® E5-26902,93,88202,513599711674Q1 2012
Intel Xeon E5-16203,63,84102,513058541772Q2 2012

And prices at AliExpress, including VAT and shipping:

€ 24 is for two E5-2690s

What type of memory and how much?

Z420 was usually sold with regular, i.e. unbuffered ECC DDR3 memory, or UDIMMs, and it must have been cheaper then, than more common registered or buffered ECC memory, which is the only type servers accept and is therefore now ridiculously cheap, even lower than € 0.5 per gigabyte. Unbuffered ECC DDR3 had also low capacity, 4 GB is the biggest I have seen, when it is the smallest capacity of registered ECC DDR3 memory in circulation. My advice is simple: get rid of UDIMMs.

Here again, HP documentation tells only a part of the story. 64 GB is supposedly the biggest amount of memory you can install on Z420, but there are 16 GB DDR3 RDIMMs and Z420 accepts full eight pieces of them for a total of 128 GB. Then there are 32 GB DDR3 LRDIMMs (Load Reduced or low voltage) for a maximum of 256 GB. 16 GB RDIMM is often quad rank memory and there are some limitations how many banks of them you can install even with Ivy Bridge CPUs and perhaps more with Sandy Bridge. On some ProLiant Gen8 servers you can install 12 DIMMs or three banks of memory, but only 8 or two banks, or only perhaps 6, if it is quad rank. That limitation doesn’t apparently apply if the memory is also of type LRDIMM.

HP documentation might actually be correct, if you don’t upgrade your CPU to a dual-processor model, which is the first thing to do when upgrading a Z420. The fastest available uni-processor, Xeon E5-1660 v2, has only 6 cores, and is most probably too expensive, if you can find one. So the correct HP provided documentation regarding memory can be found in, for example, HP ProLiant DL380p Gen8 QuickSpecs, just remember that Z420 has only 8 DIMM slots.

You can’t generally mix different kinds of memory, but there is a fourth type, which HP calls HPE SmartMemory, which can operate on regular 1.5 V and 1.35 V, the LRDIMM voltage. DDR4 uses still lower voltages, but that’s another story. SmartMemory might not be so good idea as it first appears, but I have had problems with it when mixing 4 GB DIMMs i.e. probably the oldest ones, but not with 8 GB DIMMs, and only when rebooting, not on full power down, power up cycle, and that on ProLiant DL380p Gen8.

LRDIMMs are slightly slower than RDIMMs operating on the same frequency and when already 64 GB is more than enough for any workstation use, you might just forget that option just like HP documentation did.

16 GB quad rank RDIMMs aren’t perfect either. They tend to heat up, if they are used on the four slots without fan and air flow cover.

Before adding a slimmed down old 3.5″ disk cooler, 16 GB quad rank RDIMMs were over 70 °C hot when this pretty loaded Z420 was up and running. 12 core CPU and GPU needing extra power didn’t exactly help. The cooler hangs in place with just one rubber band!

Another potential problem with quad rank memory is again speed. It should be similar to using one memory bank vs. two memory banks. Microway has an article DDR4 RDIMM and LRDIMM Performance Comparison, which also compares one and two DIMMs per channel using both types of memory.

Where to buy memory

I have bought some from eBay, but in Finland Huuto.net is more convenient and I believe also cheaper. Currently, search DDR3 ECC Reg there finds, for example, 8 x 16 GB quad rank PC3-8500R or 128 GB for € 60, shipping € 6, and HP 32GB DDR3 ECC Reg PC3L-10600L € 26 a piece and € 3 shipping.

A note about power source revisions and cable connectors

In the photo above, there is a 6-pin power connector attached to the display card. That particular Z420 came with a v2 CPU and has a newer revision of the power source, which has only one such PCIe power connector. Revision 01, sticker in the photo below, has two, labeled G1 and G2.

Newer revision 06 has the same cables from the power source, but at least the second 6-pin GPU power connector is missing.

As many display cards require either 8-pin power connector or 8- and 6-pin connectors, you’ll need some adaptors like below: