Size reading

WD External Drives External Drives for Mac
1

I have a 750GB Passport for my Mac, but the computer only says it has 697 GB available for space. why is that? I understand that it has software but not 50GB worth, right??? Please give more insight.

2

This is not because of the software, the software does not actually take any of the full size

take a look on this Knoledge base article, you will understand it:

http://wdc.custhelp.com/cgi-bin/wdc.cfg/php/enduser/std_adp.php?p_faqid=615&p_created=1034613413&p_sid=nkekOLQj&p_accessibility=0&p_redirect=&p_srch=1&p_lva=&p_sp=cF9zcmNoPTEmcF9zb3J0X2J5PSZwX2dyaWRzb3J0PSZwX3Jvd19jbnQ9MTksMTkmcF9wcm9kcz0mcF9jYXRzPSZwX3B2PSZwX2N2PSZwX3BhZ2U9MSZwX3NlYXJjaF90ZXh0PWRlY2ltYWwgYmluYXJ5&p_li=&p_topview=1

And look at the capacity of your internal drive, is the same thing, binary count of the Operating System is different than the decimal count.