Memory handling mechanics at OS level is not something I'm an expert on, but my somewhat stupid understanding of it is that certain aspects of the libraries can be shared which if the contents are unmodified. Once changed each an application would receive its own copy. The shared data would therefore, depending on page being in RAM, avoid reading the data from disk.


from http://stackoverflow.com/questions/3...rary-in-linux:
The operating system's virtual memory implementation takes care of using the same page of physical memory for multiple processes when the contents are unchanged from what's on-disk, and making physical duplicates of pages at runtime if they're written to. All of this is transparent to your application, which sees a linear 32- or 64-bit address space consisting of nothing but its own code and data.