memory.size(max=T) # gives the amount of memory obtained by the OS
[1] 1800
memory.size(max=F) # gives the amount of memory being used
[1] 261.17
Using Paul's example,
m = matrix(runif(10e7), 10000, 1000)
Now
memory.size(max=F)
[1] 1024.18
To clear up the memory
gc()
memory.size(max=F)
[1] 184.86
In other words, the memory should now be clear again. If you loop a code, it is a good idea to add a gc() as the last line of your loop, so that the memory is cleared up before starting the next iteration.