QVD file contains exactly one table. Conceptually it is similar to any typed file (e.g. CSV). A QVD file is composed of three elements.
1. A well formed XML header (in UTF-8 char set) describing the fields in the table, the layout of the subsequent information and some other meta data.
2. Symbol tables in a byte stuffed format.
3. Actual table data in a bit-stuffed format.
QVD file format is optimized for speed when reading data from a QlikView script but is also very compact. According to QlikTech reading from QVD is 10-100 faster than reading from other data sources.
Hope this answers your question!
Cheers - DV