As Word became the dominant word processor in the late 1990s and early 2000s, its default Word document format (.DOC) became a de facto standard of document file formats for Microsoft Office users. Though usually just referred to as "Word Document Format", this term refers primarily to the range of formats used by default in Word version 97-2003.
Word document files by using the Word 97-2003 Binary File Format implement OLE (Object Linking and Embedding) structured storage to manage the structure of their file format. OLE behaves rather like a conventional hard drive file system and is made up of several key components. Each Word document is composed of so-called "big blocks" which are almost always (but do not have to be) 512-byte chunks; hence a Word document's file size will in most cases be a multiple of 512.