Of all of the numerous improvements in Snow Leopard, the biggest might be its miserly use of energy. Snow Leopard doesn't just speed up your Mac, it also makes it a better environmental citizen.
Apple already had good energy saving credentials before Snow Leopard was released, including Energy Star ratings for all of its computers.
After installing Snow Leopard, many have found that their battery drain rates had decreased in Snow Leopard, indicating a lower power draw. I get about 10-20 additional minutes out of my MacBook Pro since upgrading.
I'm not certain where all of the energy saving takes place but Grand Central Dispatch could certainly manage processors more effectively, thereby saving some CPU cycles.
CNET got some hard results by testing a 17-inch MacBook Pro with Leopard and again with Snow Leopard and found that using Snow Leopard would save 10 KWh of energy per year. Sure that is only around a dollar of savings. But Apple is upgrading a lot of Macs.
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