Where should you use bigmemory?

The bigmemory package is useful when your data are represented as a dense, numeric matrix and you can store an entire data set on your hard drive. It is also compatible with optimized, low-level linear algebra libraries written in C, like Intel's Math Kernel Library. So, you can use bigmemory directly in your C and C++ programs for better performance.

If your data isn't numeric - if you have string variables - or if you need a greater range of numeric types - like 8-bit integers - then you might consider trying the ff package. It is similar to bigmemory but includes a structure similar to a data.frame.