where to buy Mac OS X 10.6 Snow Leopard

You can order it from Apple or Amazon.

If you call the online Apple Store, they may still have copies of Snow Leopard available though it's no longer listed on the web site. If they no longer have it available, you'll need to look to private sellers, and the prices are rising quickly. If you buy from a private seller, make sure you get the retail disk set (white label with a picture of a Snow Leopard), not the system disks from another model of Mac (grey label).

Regards.

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