Does anyone know how a computer cluster can be used for everyday applications, like for example video games?
I would like to build a computer cluster that can run applications over the cluster that were not specifically designed for computer clusters and still see the performance increase. One use would be for video games, but I would also like to utilize the increased computing power for running a large network of virtualized machines.
It won't help, especially in the case of video games. You have to build around the cluster; the cluster does not work around you.
At any rate, video games require sub-50ms response time on input and response,and network propagation would just destroy any performance gains you might see. Video processing, on the other hand, benefits GREATLY from the cluster as the task is inherently geared toward parallelization. It does not require user input, and output is only measured in terms of the batch process.
Unfortunately, unless you have some pretty clever operating system / software design in mind - simply connecting programs together via a cluster and hoping to get increased performance is not likely to work - especially not for video games. In order to get increased performance from running things in a cluster you have to program for it otherwise there is a good change you'd see a decrease in performance rather than an increase.
You will not be able to easily run a video game on a cluster, unless it was already designed to work on multiple machines. I have not heard of such a game. You may have some luck creating a virtual server farm, but I doubt it will be easy to get it working perfectly. If you are interested in this, one example would be amazon's EC2 service. They offer virtual machines for "rent" by the hour. Behind the scenes, I assume they have a giant cluster that is supplying all of these virtual machines.
If you have a program written for a single core, running it on a four-core processor won't help you (except that one core can be devoted to that program). For example, I have Visual Studio compiling on multiple cores on this machine, but linking is done on one core (and is annoyingly slow). In order to get use out of multiple cores, I have to either run something that can use multiple cores or run several separate programs.
Clusters are like that, only more so. All communication between the machines is explicit and must be programmed in. There are things you can do with a cluster (see Google's map-reduce algorithm), but they do require special programming and work.
Typical clusters are used either to specialize machines (one might be a database server and one a web server, for example), or to run large numbers of programs simultaneously.