Today I was messing around with an old computer that I got from my grandmother because she no longer needed it. So I decided to see if it would work as a Plex server although my hopes weren't high, needless to say It was a surprisingly great experience.
The computer I tried this on is a Dell Dimension E520 running a Intel Pentium 4, 500MB of 533 DDR2 and a really old 80GB Mechanical drive.
I installed Debian Mate, set up Plex, put a video on the HDD and opened up the web interface on my other computer and started watching and it was a really smooth experience.
At that point I was still sceptical so I started watching a video on my phone at the same time expecting that half a gig of ram to start failing but no, It was still going like a trooper!
This was mainly just a proof of concept though to see if it could work on the hardware without any upgrades. I'm currently in the middle of moving so once I've finished that I'll probably make it more of a permanent solution using a modem/router, that I have sitting in a box, as a ghetto switch.
If you want me to make a post of me setting this up permanently tell me and I'd be happy to oblige, I'll probably buy a 2-3TB drive to store all my stuff on.
Plex will run fine on old hardware, but I imagine it would struggle a bit if you wanted it to transcode stuff. By default it doesn't transcode if the device can play the file in its original format. But if you drop the quality setting to something low you will be able to get or to transcode and then you can see how it performs with that.
I was planning on doing that when I got it set up permanently. I think it'll be pretty bad though, I'll just run in the original resolution on my phone anyway since that experience was really smooth
I don't really use plex for anything but I'm pretty impressed by it. I have a 1mbps upload so I've tried streaming on the second lowest (720kbps) quality setting and thing still look pretty good. Not great but watch able. That's pretty good for real time.
I don't think I'll be streaming over the internet, mostly just local network streaming