Same files, different sizes in different partitions

[Paul Smith]

Dear All

In hde2 I have a subset of the set of files in hdb6. However, quite
surprisingly, the used size in hde2 is greater than the used size in
hdb6:

/dev/hdb6             71630968  50686876  20944092  71% /mnt/mandriva
/dev/hde2             74770560  55040436  15931960  78% /mnt/montado

How can it be?!

Thanks in advance,

Paul