PCManFM is the default file manager for the LXDE desktop.
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PCManFM is a very lightweight and simple file manager.
Pro Auto mounts drives
PCmanFM automatically detects and mounts available drives.
Pro Uses tabs
Tabs can practically be managed just as in a browser, so you don't end up with windows open all over your desktop.
Pro Can open folder as root
PCManFM can open different folders as root, this way you don't have to use the terminal to move around files for which you need root permission.
General use, and most operations, are snappy and responsive.
Con Does not include a file search option
Although you can easily search in the directory you are in by just typing in a file name, advanced searching is not possible by default.
Con Some operations are slow
Because it tries to be as lightweight as possible and tries to use very little RAM. This can unfortunately lead to it being slow sometimes.