WordPress Multisite History
With WordPress, you have ability to run multiple sites with only one installation of the WordPress platform. This was not always possible with WordPress — actually it was version 3.0 when the multisite feature was first introduced in 2010. That may seem like a long time ago; however there are still hundreds of thousands (of not hundred thousands) of WordPress users who get the idea confused with a piece of software from pre-2010 called WordPress MU (or WordPress Multi-user).
Running multiple sites under one installation of WordPress was not always possible. From August 2005 until July 2010, there was a completely separate software package (WordPress MU). In July 2010, the codebase of WordPress MU and WordPress merged, meaning that the features of WordPress MU were included in the WordPress software, rendering the WordPress MU software package obsolete. The merger of codebases brought several advantages, including the following
One codebase: Having the multisite feature available in one piece of software completely eliminates user confusion on which version of WordPress to use. Now, you use the same software package regardless of whether you want to use the multisite feature. If you do want to take advantage of the multisite feature, just a few minutes of configuration can make it happen.
Bug fixes: WordPress MU was not as popular as the original WordPress software; therefore, the MU project didn’t attract as many developers to contribute code, fixes, and additional feature development. When the merge occurred in July 2010, the multisite feature gained the massive WordPress developer community, making bug fixes and new features a quicker and easier process.
Easier interface: The interface and Dashboard features for the multisite feature in WordPress is much easier to work with, mainly because it works in tandem with the other WordPress settings and features you’re already familiar with.
In the past, the WordPress codebase would be updated, and those changes would be rolled over to WordPress MU with any additional fixes. Occasionally, WordPress MU users had to wait two to four weeks or longer for updates. Because the number of users familiar with WordPress MU was far less than WordPress, feedback for bugs was also slow. Even though more than 95 percent of the two codebases were identical, the remaining code in WordPress MU did the bulk of the work maintaining multiple blogs.