Microsoft Certification Ebook

Introducing Master certifications
The new Microsoft Certified Master series offers advanced technical training and certifications on Microsoft technologies that go beyond any product training offered outside of Microsoft today. IT professionals who successfully complete the training program and certification testing validate their skills as product experts who successfully design and implement solutions that meet the most [...]

70-640 is basically being replaced by 83-640 in English language. 70-640 was just available until the end of May and afterwards you can only schedule and take 83-640 exam (English version, the rest versions should become available shortly).
Microsoft is using the 83-### numbering scheme to distinguish lab-based exams from the traditional multiple-choice and interactive item-type exams [...]