Simplify the following text for a Grade 7 native English-speaking person.
Original: Volume management treats PVs as sequences of chunks called physical extents ( PEs ) . Some volume managers ( such as that in HP-UX and Linux ) have PEs of a uniform size ; others ( such as that in Veritas ) has variably-sized PEs that can be split and merged at will .
Simplified: PVs are split into small chunks of even size ( a default of 4 MB on HP-UX ) called physical extents or PEs .