Why is it that FileInputStream read is slower with bigger array

Question

If I read bytes from a file into a byte[] I see that FileInputStream performance worse when the array is around 1 MB compared to 128 KB. On the 2 workstations I have tested

Answer 1

Optimal buffer size depands on file system block size, CPU cache size and cache latency. Most os'es use block size 4096 or 8192 so it is recommended to use buffer with this size or multiplicity of this value.