Unlike execution time, R does not provide any good tools to profile CPU utilization and disk I/O. Even the memory profiling tools in R might not provide a complete or accurate picture. This is where we turn to OS-provided system monitoring tools to keep an eye on the computational resources as we run R programs. They are task manager or resource monitor in Windows, activity monitor in Mac OS X, and top in Linux. When running these tools, look for the processes that represent R (usually called R or rsession).
The information that we get varies depending on the operating system, but here are the key measures of R's resource utilization to keep an eye on:
% CPU or CPU usage: The percentage of the system's CPU time used by R
% memory, resident memory, or working set: The percentage of the system's physical memory used by R
Swap size or page outs: The size of memory used by R that is stored in the operating system's swapspace...