Microsoft Word is a word processor and was previously considered to be the main program in Office. Its proprietary DOC format is considered a de facto standard, although Word 2007 can also use a new XML-based, Microsoft Office-optimized format called .DOCX which has been standardized by Ecma International as Office Open XML and its SP2 update will support ODF and PDF. Word is also available in some editions of Microsoft Works. It is available for the Windows and Mac platforms. The first version of Word, released in the fall of 1983, was for the DOS operating system and had the distinction of introducing the mouse to a broad population. Word 1.0 could be purchased with a bundled mouse, though one was not required. The following spring Apple introduced the Mac, and Microsoft released Word for the Mac, which became the most popular Mac application and which, like all Mac apps, required the use of a mouse.