Intended as an upgrade path for existing MSXML 6.0, MSXML 3 and MSXML 4.
MSXML 6.0 Service Pack 1 as improved reliability, security, conformance with the XML 1.0 and XML Schema 1.0 W3C Recommendations, and compatibility with System.Xml 2.0
MSXML 6.0 SP1 is intended as an upgrade path for existing MSXML 6.0, MSXML 3 and MSXML 4.