i want to know if the mac os 10.6.8 update free
If you're running Mac OS X 10.6 to 10.6.7, yes.
If you're running Mac OS X 10.5.8 or earlier, no. If you're a member of an organization which makes heavy usage of Macs, they might have paid for it and put it on their LAN, in which case it's free to you.
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