You can view the current usage of disk blocks: which blocks free, which blocks are occupied by which files.

可以查看当前磁盘块的使用情况：哪些块空闲，哪些块被哪些文件占用。

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Meanwhile, I can use the free GPS on my smart phone, which tends to find me a few blocks away from where I really am, but it gives me a route that takes me where I need to go.

FORBES: Why To Think Twice Before Buying That GPS Device