QVD files are not compressed, but they are an efficient format, especially for low cardinality data. The distinct values of each field are stored in a symbol table, and the rows are represented by pointers into the symbol table. The pointers are made up of varying bit lengths depending on the number of distinct values, so for example, a bit length of 3 can manage up to 8 distinct values, and a bit length of 10 can handle up to 1024 values. These pointers are bit-stuffed into a single binary value for each row in the QVD. So the size of a QVD is determined by the number of columns and the cardinality of the columns as well as the number of rows.
Qlikview and Qlik Sense store the data in a similar manner. Part of the value of QVDs is that they can be loaded almost directly into Qlik with a minimum of work, especially for an optimised load (no extra fields, simple "exists" filtering only).
Qlikview has an option to compress the model (QVW) to an extent set in the document properties. I am not sure what compression, if any, is used by QS in QVF files. The size of QVW/QVF files is determined by the requirements for the app layout as well as the data.
In QS Enterprise, the apps are stored in the Apps subfolder of the shared Qlik folder set up when QS was installed. The files are named as GUIDs (the internal app ID) without an extension.
Logic will get you from a to b. Imagination will take you everywhere. - A Einstein
