This is a problem which is CPU-bound rather than IO-bound. Ruby, Python and the like won't typically show a great difference in speed when the majority of time

This is a problem which is CPU-bound rather than IO-bound. Ruby, Python and the like won't typically show a great difference in speed when the majority of time is spent in IO operations (like web crawling, or text processing, running web apps, querying databases, etc), because the bottleneck on performance comes mostly from the slow reading of files and network sockets. In this case, though, the operations are mostly dependent on just doing computation, so a high-level interpreted language like Ruby really shows its limitations. This is one of the (many) reasons why although languages like Ruby and Python are great for rapid development, on-the-fly updates and other reasons, it can pay dividends to be fluent in a high-performance language. It wouldn't even need to be C (although this wouldn't be hard to do in C) -- a language like D would give you excellent performance and nearly as easy development as Ruby.