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what are the major diffarences between jira software 6.0 and 7.0
For the updates on 6.x, see https://confluence.atlassian.com/jira064/production-releases-720413057.html
When 7 was released, there were two main changes related to the JIRA Software and JIRA Service Desk being made into "applications" which has a big effect on the way users are handled.So there are now three sets of notes. Most people have Software, so start at https://confluence.atlassian.com/jirasoftware/jira-software-release-notes-776821069.html