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Recently I read 30-50% of more heap is required on 64-bit beacuse of the memory layout in 64-bit archicture.

This Includes

1.the Object Header which are 12 bytes on 64-bit JVM which adds some overheads as compared to the 8 bytes on headers on 32-bit

  1. Object references can be either 4 bytes or 8 bytes on 64-bit While on 32-bit it is 4 bytes

My Question is why we need 12 bytes of header in 64-bit JVM what difference does it makes ? and so is for the Object Reference too WHY ?

Ankur Anand
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    Because pointers of a 64bit process are twice as large (8byte) as those of an 32bit system (4byte)? – Robert Apr 21 '15 at 15:56
  • Duplicates http://stackoverflow.com/questions/26357186/what-is-in-java-object-header and http://stackoverflow.com/questions/29143399/size-of-java-object – apangin Apr 21 '15 at 16:27

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