Do all OSes still use a dumb LRU algorithm for caching?

I am backing up a partition from SystemRescueCd using dd and gzip. Occasionally I run ls to see the size of the output file. If I haven't used ls in a bit, the DVD drive spins up. So, it seems like Linux is using a dumb "least recently used" algorithm for caching, and the partition backup I/O is constantly removing ls from the cache. Do all operating systems still use such a dumb algorithm?