The advantage of this format is that the size of the disk image is not the same as the physical file representing the image.

这种格式的优点在于磁盘映像的大小与表示映像的物理文件的大小不同。

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There is no need for a daily download of a file in a specific format that has to be supported by the physical platform of your choice.

这样就无需每天下载一个特定格式的文件，也不用管你选择的物理平台支持哪种文件。

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