I picked up an HP Thin Client T620 off eBay hoping to use it as a retro game/htpc kind of setup. It came with Windows 7 embedded version on a 16gb M.2 SSD. I purchased a 128gb M.2 SSD and have been trying to install either Windows 7 or 10 with no luck. The problem is when I run Windows (7 or 10) setup on the T620 it shows the new SSD as only having 1023mb of space, which of course means it wont install windows, but when I stick the SSD into my main PC running Windows 10 it shows the full 128gb. I have tried initializing and formatting the new SSD both from T620 and my main PC, as well as making a full size partition, I have updated drivers and BIOS on the T620, nothing I do has changed it from showing only 1023mb of space when it is in the T620.

I am out of ideas!

Check for a bios/firmware update for it.

I've updated drivers and bios, didn't help sadly.

its a “thin client” meaning it doesn't run a full fledged OS, but rather let a server handle most of the processing. i think they run a windows embedded OS like windows CE or something along those lines.

ETA:

try this https://docs.microsoft.com/en-us/windows/iot-core/downloads

You 2 are correct that they run embedded Windows from the factory, but YouTube videos and some forum posts I've seen show several people have successfully done what I'm trying to. With a storage upgrade they will run normal Windows OS and even run retro games. I'm basically trying to make a Windows version of my Raspberry Pi 3b+ RetroPie setup and use it for streaming to the TV.

This guy upgraded the SSD, installed Windows and even ran Halo 1 and similar games with an external video card added on, this PC is capable of what I'm trying to do, I just can't get to that point lol

1080p gaming on a HP T620

Have you got another drive you can try, to see if maybe it's just THAT drive it doesn't like?

What sized drive does BIOS say you have?  If BIOS sees the entire drive, then the install media has trouble reporting size.  In my search I found one case of a user having trouble using an NVME card, however that thread was never resolved (resolved by not using T620)

Looking on Youtube, it appears others have been having good luck with the 620 with regards to memory and drive upgrades, so that brings me back to wondering if that specific model of M2 drive  might be fussy with the T620?

I have re-purposed thin clients into light use pc's in the past, and the T620 is capable of running Win7 and Win10 reasonably with 4-8GB of ram.  Depending on the model, some have quad core AMD cpu's.

I don't have any other M.2 drives to try, but I've been wondering about that as well.

I'll have to look again, I don't remember what it showed.

Yeah I made sure to get one with the quad core and 4gb of ram

Have you verified whether you have M.2 SATA or M.2 NVMe?

Each does not run in the other type of slot.

I bought an M.2 SATA drive to replace the M.2 SATA it came with so should be good there.