CentOS 7.0 is un updated build of the project's legacy branch, compiled from the source code for Red Hat Enterprise Linux 6.8. CentOS 6.9 is based on source code released by Red Hat, Inc. for Red Hat Enterprise Linux. There are many fundamental changes in this release, compared with the past CentOS 6.9 releases, and we highly recommend everyone study the upstream release notes as well as the upstream technical notes about the changes and how they might impact your installation. All updates since the upstream 6.9 release are also on the CentOS 6.9 mirrors as zero day updates. When installing CentOS 6.9 (or any other version) from any of our media, you should always run 'yum update' after the install.