The Finder, the central point for managing files and folders in Mac OS X, has been completely rewritten in Snow Leopard. But you'd hardly know it from looking. This new version, which was written using the Cocoa frameworks required for any 64-bit application, looks more or less identical to the older version. Apple says that this new Finder is much more responsive than the older model due to the complete rewrite, support for 64-bit mode, and increased threading using the new Grand Central Dispatch technologies.
The biggest changes in the Finder have to do with icons. Icons can now be as large as 512 by 512 pixels, four times as big as Leopard's largest (256 by 256). There's a slider in the bottom-right corner of any window in Icon view, which lets you crank the size of the icons in that window up or down without invoking the View -> Show View Options command and adjusting the controls there.
Apple is taking advantage of those big icons by putting live previews inside them. In Leopard, Apple introduced Quick Look (which lets you view the contents of a file by pressing the spacebar) and Cover Flow (which lets you view document previews in a Finder window). In the new Finder, you can get an even quicker look by just hovering over the icon in question with your cursor. If it's a multipage PDF, you'll be able to view the entire contents of the document, using next- and previous-page buttons to navigate. Hovering over a movie will reveal playback controls--and yes, this means you can watch a QuickTime movie in its icon.
If you use external hard drives, thumbdrives, or the like, you've probably run into one OS X's annoyances: sometimes your Mac just loves your external volumes so much that it won't let them go. If you've ever tried to eject a volume only to have OS X tell you the volume is in use and can't be ejected, or if you've ever been scolded by OS X for disconnecting a volume that was still mounted, you know what we're talking about.
In Snow Leopard, dismounting drives is vastly improved. Snow Leopard's new eject manager improves on the old method in two ways. When you first attempt to eject a disk, the eject manager actually sends out a signal to its own subsystems and other programs, asking them to relinquish their hold on the volume if that's possible. If that fails because a program really is using the drive, Snow Leopard will bring up a window telling you which program doesn't want to let you eject the disk. You can then switch to that program, quit out of it, and eject the disk.
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