Go wuth what you have. Old laptop? Works! Old desktop? Also works! Old android phone? Might work! (VM/terminal)

If you have a device that can run Linux, start with that. Once you get some usage you can understand if you need an upgrade, and what kind. Maybe you will findout that this old laptop that you had works perfectly and you can sace money on buying a server.

If the size and low power consumption of the Pi are what appeal to you, you can try a getting a used thin client. Lots of suggestions and specs here: http://parkytowers.me.uk/

Depends on what you want the server to do. A Minecraft server and a Pihole server have vastly different requirements. As a general rule, any old laptop or desktop will do, think on requirements for your grandma and that should cover most (except gaming servers) needs.

I use a random micro PC with Ubuntu installed. 2tb nvme, 16gb ram, not even sure what the cpu is

A computer. Seriously that’s it. Of course depends on your use case (media servers usually need more than a web host for example)

Even a Commodore 64 can be a server depending on the service it has to give.

Literally any old PC is likely fine. It may be slow, it may struggle or even fail with some of the very complex software (perhaps you will encounter timeouts, or you will spend so much time waiting for memory to swap in or out to disk that it won’t be worth using) but you can run Linux itself on a potato and if your machine isn’t powerful enough, maybe you can get a second one and run different stuff on each, or just scale down your expectations and don’t try to self-host LITERALLY everything just because you can. Certain services are very intense, others will run on a very small piece of a potato.

The joke is electricity and Linux.

The real answer is the free hardware.

My main reliable is from 2008? It cannot do modern virtualization due to not having the CPU instruction sets.

Had this link in my clipboard for a different comment but it fits here as well: https://hackaday.com/2025/04/09/self-hosting-a-cluster-on-old-phones/

In all honesty this may be a bit advanced depending on your experience and more importantly nerves, but any old PC/laptop can be turned into a server.

As for parameters I would suggest you go to the apps you plan on running and check their minimum requirements.

Anything that does the job is good enough. At its core a server is just a regular PC with a dedicated purpose and software. Sure, there are specialized hardware better suitable and purpose built, but it’s not a requirement.

I for one prefer 19" rackmount stuff with disk bays in the front, but that’s more of a convenience than anything.

UPS is nice, but it’ll work without it.

I’ve had to deal with the Brazilian computer market and how it’s ridiculously overpriced due to import fees, so in your situation I’d just get any hand-me-down computer. Servers generally don’t require much unless you’re doing something special or intensive.

Get your hands on whatever you can find for free or dirt cheap (laptop or desktop doesn’tmatter), install linux, and you have a basic setup that you can work with. If your use case requires more, then that’s something you can accommodate in the next iteration of your server.

What are you intending to run on this server?

• If it is just PiHole, you can basically get the weakest computer you can find.

• If you want lots of storage space, you will need to make sure you have a case and motherboard that will accommodate the drives.

• If you are running encryption on those drives as well, you will need a CPU more powerful than what comes in a Pi, but nothing crazy.

• If you are running lots and lots of VMs, you will want lots of RAM. A linux VM will use maybe a few GB each depending on what software each is running internally, a windows vm will use a bit more.

• If you are doing AI workloads, you will need a graphics card.

You have to have an idea of what you’ll run on it first.

Old corporate desktops will do for a NAS and basic light services. Look for one that has three drive bays plus an NVMe slot.

Take a look at some N100 devices (or N95/N150).

When I started my media server in 2020 I used e-waste from my building. Had an i7 3770, 16gb ddr3 ram and an rx460 graphics card. I ran jellyfin, ultrasonic and audiobookshelf for 10-15 people with no problem on this hardware. Anything made within the last decade should provide a good starting point for you.