PCManFM is the default file manager for the LXDE desktop.
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PCManFM is a very lightweight and simple file manager.
General use, and most operations, are snappy and responsive.
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.
Pro Supports "quick-directory" typing
While in a PCManFM window, typing either a "~" or a "/" will automatically start typing into the location bar, allows for tab completion, and pressing Enter goes straight to the typed directory.
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 use tabs instead of new windows
Use tabs to open fewer windows. New tabs automatically start in the same location.
Pro More RAM is available for other processes, and the system uses less swap
Overall, the system becomes faster.
Pro Auto mounts drives
PCmanFM automatically detects and mounts available drives.
Con Can't extend with scripts
Unlike Nautilus and Caja, this can't extend with scripts. If script extension is added it can become a really good FM.
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.