In this chapter, we saw how R programs can sometimes encounter the three constraints faced by computing performance—CPU, RAM, and disk I/O. We looked into R's design and learned how its interpreted and single-threaded nature can cause it to run slowly, and how it can encounter memory and disk I/O limitations when data becomes too big to fit into the RAM. Finally, we looked at how the design of R code plays an important role in determining the performance using a comparison between two implementations of the Fibonacci function with very different performance characteristics.

These performance issues are not insurmountable. The rest of this book will show you different ways to overcome or work around them and unlock the hidden potential of R.