HP t420 thin client - penny pincher of marginal serverage

Welcome to the short and succint guide to the HP t420

(Also known by HP internal codename Xing)

So why should you care (as a home labber)?

It's a small-ish thin client, roughly 180mm W x 140mm H x 35 mm D , ~0.88 Liters, released May 2015, general availability in Q1 2016. It's about the same size as a typical Arris surfboard modem, and at the price it commands on the secondary market, it's an interesting Raspberry Pi2/3 alternative.

In the t420, you have a custom AMD Jaguar based APU within the AMD Kabini family. If you are familiar with the GX420CA in the t620 Plus, think of it with half the cores, half the threads, the CPU downclocked to half the value, and the GPU downclocked to 1/3 of the original, and the thermal TDP set to 1/4 (6 watts instead of 25).
In addition to that, 2 GB of RAM is soldered onto the SoC, and the storage is now implemented with an internal USB3 slot.

It's stupid cheap - I got mine for about 27 USD with a power brick, which compares well with a Raspberry Pi 2. Don't pay more than 40 USD for one (including shipping/handling, taxes and a power brick)

How much CPU and GPU firepower can I expect from one?

Don't expect too much out of a dual core 1GHz AMD Jaguar based APU - it's like an AMD A6-1450 sold in some very late production Netbooks from the likes of Acer.

The GPU onboard is a GCN 1st Gen with a UVD3 video decoder - 1080p H264 decoding is available, but no 4K decode, no H265, no VP9, and certainly no encoding except VC1 in 2K. The GPU itself has 2 Compute units of 128 Shaders: 8 Texture Mapping Units: 4 Render Output Units. Raw power-wise it's about 55 Gigaflops peak - fairly competitive against, say, the Raspberry Pi 2 or 3.

Base configuration as shipped is 2GB of RAM soldered, and a 4GB eMMC inside the USB-A 3.0 port.

Base OS is HP ThinPro (a variant of Ubuntu Linux), ThinPro Zero client or Windows 10 IoT edition x64.

What’s my path to expandability?


- 1 Internal USB 3.0 port (fits a Sandisk Cruzer Fit just fine)
- 1 MiniPCIe slot (note: Not M.2) - there are probably some MiniPCIe NICs out there.
- 2 USB2.0 ports in the back, , 2 USB 2.0 ports in the front

Upgrade Compatibility with...eh, never mind.

Is there a guide to working inside the chassis?

HP has a policy of providing teardown/e-cycling guide for their hardware, and this is the one for the t420 (it's a PDF file). Note that the teardown guide always reference the product codename and it looks like the factory assembly procedure but in reverse.

OS Compatibility with the t420

The following bas been tested and known to work:

Debian Linux 10
Proxmox 6.2 (have fun getting multiple VMs of over 512MB RAM allocations running...although you'll be surprised)
VMWare ESXi 6.5 (muhahahahahahhahah please don't)
HassOS (some home automation thing. Wanna pinch pennies?)
pfsense (did I mention that the AMD Jaguar has AES support, and you can use USB NICs?)
FreeDOS 1.3 (surprisingly decent for retrogaming)

How much can I expect to pay for one?

As of Q3 2020, about 25-40 USD for a refurb unit, but expect it not to have built-in Wifi.

  • It's cheap and works better than a Raspberry Pi 2 or 3. And you don't have to buy a case, a power brick and a MicroSD card for it.
  • You can just stick a Sandisk Cruzer Fit or even a MicroCenter special flash drive in there, park it in a closet and forget it. Hell, use a USB to MicroSD adapter and you can use the same media as your Pi!
  • Runs x64, so legacy software works, dammit!
  • Fairly small and conspicuous
  • Silent - no moving parts
  • Sips power (1w idle, 6-8w fully loaded)
  • More common than a cockaroach in an NYC subway station (so very cheap)

• No IPMI, and no VPro. Remote admin - what the heck is that?
• RAM not upgradeable, and storage is USB3 only.
• GPIO pins? What the heck is that? (If you are planning to bitbang the t420 is not for you)
• It's not very fast but it sure is slow. But then, people use Pi2s, 3s and beaglebones. It's also not that performant compared to its Atom equivalents (but those are harder to come by).

So, what can I do with it?

- Use it as a thin client.
Install OpenVPN, Give one to your mom or mother-in-law (mount it behind her monitor) and point it at a VM that you control (with an hourly filesystem snapshot?). Dare her to mess it up.

- Plug in a USB2 NIC and run a low usage home firewall via pfsense.

The default port is a Realtek 8111, and if you want to, dremel a hole in the casing and run a MiniPCIe Realtek NIC inside.

- Low performance hypervisor for retro-computing

In case you still mess with Windows NT 4.0 SP4 / Win2K SP3 or Novell Netware, well, this is where you set up an old domain controller and segregate it away from the main populace.

- Somewhat credible FreeDOS machine

Well, if you want to play oldschool DOS games, you can load it up with FreeDOS and sbemu, copy the DOS games over and it'll play games until the cows come home (well, some DOS games)

- Run MUNT with it

Got a USB-to-Midi interface and an oldschool machine with a Midi port, and you can't afford a Roland MT-32 for DOS games? Easy - Debian Linux + MUNT, buy the Roland ROMs, set it up and plug it to a pair of decent speakers. Instant MT-32 for those who likes to play Lucasart's Loom with the MT32 patch suite (well, assuming you don't finish the game in less than an hour)...

Are there similar products out in the market today?

Sure - the HP t520 is a stronger machine overall, and it does have a single RAM slot (a single 16GB DDR3L SODIMM to max it out is 150 USD, though). However, it's also a least 10 dollars more expensive.
There's also the Dell-Wyse 3040, but that one has eMMC soldered in with minimal upgrade possibilities. It's a also a current Dell product so they are not that cheap.
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