Sitecore 7 has several new features that you won’t find in its predecessor. Most of them are under the hood, mainly related to search features added in the CMS and how this helps editors manage content faster, properly, and more easily.
Previous Sitecore versions have some restrictions on child items. Max children are limited to 100, but in Sitecore 7 there are Item Buckets. These item buckets do not have restrictions on the number of children and can contain millions of child items. For instance, children are not displayed in the content tree. Instead, Sitecore uses a search box tool to locate the items inside the content editor display. Field values can appear on the search results page and results can be refined with facets. Besides this, there are quick actions that can be applied to a large number of items simultaneously, which is a very helpful tool for content editors.
Sitecore 7 has implemented several search features that have become a primary tool within the CMS to manage content. In addition, Sitecore 7 includes Solar, an open source search platform. This search platform is useful for searching through large amounts of documents. Using Solr integration for search is the same as using a file-based Lucene index but instead of storing information in file-based indexes, information is stored remotely on the Solr server.
Another great feature of Sitecore 7 is better management of Datasources and references to other items. It now uses IDs instead of Paths because a Path could be changed but IDs are always the same. This will reduce many issues at the time content editors move items in the content tree, so references to its Datasources will not be lost.
The main reason most upgrade to Sitecore 7 is scalability. Most of the new features are oriented to get a better performance and manage large amounts of content. New features like search results, quick actions, and facets provide a more intuitive interface for content editors making easier for them to locate, edit and organize content.