~~Title: Basic Concepts ~~
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There are a number of concepts in Opus that may be different from other file managers you have used. While we try to avoid the use of jargon or geeky terminology there are some terms used in this help file that you may not be that familiar with; we suggest having a quick flip through the Basic Concepts section to familiarize yourself with some of these concepts.

  * **[[:basic_concepts:the_lister|The Lister]]**: Listers are what you might call the Opus "main window" - in a traditional file manager, they would be the main window. Listers (the name is historic) contain file displays (where the contents of directories are shown), folder trees (presents your file system as a tree structure for easy navigation), toolbars, and various optional "panes" like the viewer pane, the metadata pane, etc. You can open as many Listers as you like. 
  * **[[:basic_concepts:explorer_replacement|Explorer Replacement]]**: Opus has the option to operate in Explorer Replacement mode. In this mode, most actions that normally result in the opening of an Explorer window (pressing the <kbd>Win+E</kbd> key, double-clicking on an icon on the desktop, etc.) will instead open an Opus Lister. This is the mode we recommend you run in. 
  * **[[:basic_concepts:source_and_destination|Source and Destination]]**: As well as the traditional copy/cut/paste method of file management you're probably used to, Opus provides an alternative method that uses the concept of "source" and "destination" folders. Instead of browsing to the files you want to copy, copying them to the clipboard, then browsing to the destination folder and pasting them in, this alternate method lets you display both the source and destination folders at the same time (either using two separate Listers, or with a single Lister in dual file display mode) and copy files from one to the other in a single action. 
  * **[[:basic_concepts:selecting_files|Selecting Files]]**: There are a number of ways to select files for operations; other than the standard methods using the keyboard or mouse, you can select using a wildcard match on the filename, or use a filter to select files by attributes or metadata. Opus also supports a checkbox mode which lets you manipulate files (by double-clicking or drag-and-drop) without affecting their selection state. 
  * **[[:basic_concepts:searching_and_filtering|Searching and Filtering]]**: Searching is the process of locating files or folders that may not be in the currently viewed location - Opus supports Windows Search for indexed search, as well as its own powerful search engine that lets you build complex queries to find files based on attributes and metadata as well as filenames. Filtering is the process of hiding, or masking out, files and folders from the currently viewed location. Opus provides a number of ways to do this - the easiest to use is the Filter Bar, which lets you quickly show a sub-set of files by simply typing a wildcard pattern into the file display. 
  * **[[:basic_concepts:sorting_and_grouping|Sorting and Grouping]]**: The file list can be sorted by a single field or by multiple fields, and you can also group the file list by any field with collapsible groups. 
  * **[[:basic_concepts:folder_options|Folder Format]]**: This is a powerful system that lets you control exactly how your folders will appear - you can define the view mode, sorting and grouping options, etc, and permanently assign them to a folder, a folder and its children, a "type" of folder (based either on the disk type or the contents of the folder), or multiple folders using wildcards.  
  * **[[:basic_concepts:expandable_folders|Expandable Folders]]**: Opus lets you expand folders in the main file display just like in the tree, so you can see the contents of sub-folders without having to change location.
  * **[[:basic_concepts:flat_view|Flat View]]**: The Flat View system lets you "collapse" the contents of all the child folders of the current location, and make them appear as if they are all in the same physical location. Flat View can show a truely flat list of all sub-folders, or it can display the contents of sub-folders in a hierarchical structure. 
  * **[[:basic_concepts:folder_sizes|Folder Sizes]]**: See the sizes of folders just like you can for files. Opus integrates with [[https://voidtools.com|Everything by voidtools]] for fast folder size calculation.
  * **[[:basic_concepts:virtual_file_system|Virtual File System]]**: The real file-system is where you store your files and folders - generally contained on your hard drives, USB drives, etc. The virtual file-system is a concept that Opus uses to describe file-systems that aren't stored in this traditional manner. For example, File Collections are a virtual file-system because they are a collection of files stored on traditional media, rather than the underlying folders themselves. There are a number of concepts that are specific to particular virtual file systems - File Collections, Libraries, Archives and FTP are all described in this section.