CodeIgniter is based on the popular MVC development pattern. While controller classes are a compulsory part of development in CodeIgniter. Models and views are optional in CI. CodeIgniter can be also modified to use Hierarchical Model View Controller (HMVC) which allows developers to maintain modular grouping of Controller, Models and View arranged in a sub-directory format.
CodeIgniter is a Framework for developers who build web applications using PHP. CodeIgniter has a goal to enable you to develop projects faster than you were writing code from scratch, by providing a rich set of libraries for commonly needed tasks, as well as a simple interface and logical structure to access these libraries. CodeIgniter is a very fast framework and best for development. It really has better performance than other frameworks.