Directories are provided for data recorded on a magnetic tape in the form of files having data demarcation signals, such as filemarks. Data storage logic arranges a map of the tape in fixed regions; establishes a window at each intersection between fixed regions, the window extending into at least one of the regions; determines whether at least one data demarcation signal is located in a window; if so, selects and identifies the properties and location of one of the data demarcation signals as within the window. If no data demarcation signal is present, the directory indicates an absence of data demarcation signals within the window.