Random access is always slower than linear reading. Even if you aren't going to disk, you can avoid blowing out the processor cache and having to get from main

Random access is always slower than linear reading. Even if you aren't going to disk, you can avoid blowing out the processor cache and having to get from main system memory. Ram is a cache, and L2 is a cache, &c. What you are doing is pretty normal "old-school" unix programming.