I guess it'd be better if you provide more information because it depends how complicated the games are, how well the server program is coded, and of how many players one instance of a game you speak of consists.

i.e. does server need to calculate real time 3d physics? or water physics etc.


my 2 cents without too much experience
if the game does not require server to calculate expensive things or game instances don't take 50 players, any computer/server you buy with todays specs should be able to handle it easily.

I was wondering today what sort of server one would buy if one wanted to set up one's own server to host multiplayer games on. I don't even know what to search for, but I'm thinking of something that would fit under a desk and be able to handle something in the neighborhood of five to ten concurrent real time games.

The FAQ has a lot of information on this, as does a few previous threads talking about things like closets vs co-location vs data centers vs cloud provisioning.

The first question is: What specific games? A game of NetHack requires a lot less CPU power than a game of Battlefield.

However, it's not just the server hardware that matters -- how you connect it to the internet, and how you provide services to the players, matters a lot, too!

Generally, you probably want to look for "dedicated servers" or "root servers" or something similar. Typically, these run for between $79 and $299 per month, depending on CPU, RAM and other capacity requirements, and usually come with the necessary bandwidth hook-ups. These are servers you rent, they are screwed into some rack in some data center somewhere, and you just get remote access to install OS and software on the servers and run them. You really don't want to have anything that people rely on be located under your desk, as emergency power, connectivity, climate/cooling, and pretty much everything else will be worse there than in a dedicated space.

For real-time gaming (FPS style), I would recommend against virtualization and "virtual private server" and "cloud" set-ups, because they add significant jitter to the CPU execution which will end up showing up as lag spikes in the gameplay.

I was wondering today what sort of server one would buy if one wanted to set up one's own server to host multiplayer games on. I don't even know what to search for, but I'm thinking of something that would fit under a desk and be able to handle something in the neighborhood of five to ten concurrent real time games.

First of all:

What type of connection do you have access to and what type of game are we talking about ?

for a game like Battlefield you probably want a 100/100 connection and a fairly beefy server to host 10 concurrent games, a modern 4 core cpu might be a good choice here.

for a game like the small online games microsoft includes with Windows you could host 10 or even more games easily on a smartphone with a 3G connection.

Say it's a real-time game with 2D physics and 4 players per game. I'm looking for a general type of server, not a recommendation for a specific server to purchase, so I shouldn't have mentioned such a tight range of server instances. I clarify in the last paragraph.

I understand that you can use a desktop computer to host server instances, and that you can purchase server space on other servers. But I want to find a computer I can buy, built for the purpose of hosting a server, that doesn't come with a monitor, soundcard, or graphics card.

So far I've only found servers intended for small businesses to use to store media. They have lots of memory but are not impressive performance-wise. I want to find a high performance but low memory server of the size to fit under the desk. (I didn't mean that I literally wanted to store a server under a desk. The desk was used to illustrate the size I am thinking of.)

The only things that are different between server computers and a regular desktop computers are the quality of parts and backup systems. Depending on how stable you want your server(s) there's a wide variety of stuff you can buy.

Check here: Newegg Servers

So far I've only found servers intended for small businesses to use to store media.

You can always roll our own from parts. Motherboard + CPU + RAM + boot disk (unless you PXE boot) + power supply + enclosure + OS == server. I recommend two sockets, and a six-core Xeon per socket. You probably also want 32 GB of RAM. Personally, I always specify SSD drives for machines these days, but if you need vast amounts of persistent storage for the "long tail" of history, spinny disks may still make sense.
I highly recommend Linux or perhaps BSD for "headless" servers. Windows really, REALLY wants you to click stuff to manage, which gets old very quickly and is hard to automate.

If you want to buy something just search for "rack mount web servers" or go to a place like dell.com (or hp.com, or ibm.com, or ...)
A Dell R510 (2U, 2 sockets, space for storage) or R610 (1U, 2 sockets) seem like decent options. http://www.dell.com/...weredge-r510/pd
Dual hex-core Xeons, 32 GB of ECC RAM, dual 250 GB SATA drives for RAID 1 will run you about $6k.

A server is just a computer, perhaps built with more redundancy in mind, but essentially so. What really makes it a server, though, is what you install on it (eg, what service it provides), and how you connect it to the network (eg, how available it is). Strictly speaking, you don't need a fancy motherboard, processor, storage solution or gobs of RAM, as long as its got sufficient quantity and quality of each to provide the desired quality of service for your users.

Hardware wise, figure out your requirements, then buy a white-box solution or roll your own. Software wise, use whatever OS is familiar and which your game server runs on, whether that be Windows, OS X, or some Linux/Unix/BSD flavor -- though in general, most larger server installations prefer the latter for its price (free) and customizability.

The connection and redundancy issues are what generally makes it unfeasible to do home-based hosting -- What happens when your internet connection is disrupted, a component fails, you experience brown-out, or are hit with some kind of localized disaster such as a fire or flooding? Hosted solutions generally have 2 or more direct connections into the backbone of the internet from different providers (in case one provider goes down), receive power distribution from 2 or more grid providers, massive battery banks and high-capacity on-site power generators, each physical server might have redundant power supplies, RAID Mirroring and nightly automated redundant backups plus less-frequent off-site backups, or even near-realtime fail-over to alternate sites in case one data center is hit with some kind of disaster, or in case of a large-scale internet outage... the list goes on.

This is not to say that every server for every little indie game needs this level of redundancy (until it does ) but it is to say that you do get rather a lot for your money from hosted service providers when you think about it.

In addition to the usual CoLo-hosted options, there are a few services which specialize in game hosting. Usually their services are used by PC-gaming clans to host a permanent clan server for whatever game it is that they play, but most are happy to let you install and administer whatever software you wish -- of course, they won't provide technical support for your software, it'll likely be limited to OS setup, networking issues, and power-cycling the machine if it becomes necessary -- but their plans are at least structured around the types of services games need (eg, moderate disk space and bandwidth, high-powered CPUs, plenty of RAM, but perhaps limited or no support for databases or other "enterprise" needs).