extra allocation?

Hi all,

  making this:

  (make-array 16000000)

  in trial version produces a report:

Error: An allocation request for 64000016 bytes caused a need for 169082880
more bytes of heap. [...]

  my question is: why allocation request for ~64Mb causes request 
  for ~169Mb more of heap? 

kind regards,
Valery A.Khamenya
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Bioinformatics Department
BioVisioN AG, Hannover