Code culture clash
Yahoo principally uses FreeBSD, which is well regarded for its stability and its strong security.
Yahoo also uses the Java programming language as well as the PHP scripting language, which is widely accepted as a tool for rapidly building and maintaining the dynamic Web pages that are at the heart of its many Web services. Indeed, the creator of the PHP language, Rasmus Lerdorf, is an infrastructure architecture engineer at Yahoo.
Finally, Yahoo relies heavily on a parallel programming tool that will take a program that is written for one computer and extend it to run on hundreds. This allows Yahoo to scale up the power of a search engine algorithm, for example. (The program was invented at Google, but Yahoo uses an open-source version called Hadoop.) Microsoft uses its own competing system, developed in its research labs, called Dryad.