Before you can get started doing Ruby on Rails development, you have to set up the software that you will need to develop, run, and test your applications. There are at least three pieces of software that you will need. They are:
The Ruby language runtime
The Rails framework
A database (such as MySQL, PostgreSQL, SQLite, Oracle, and DB2)
If you install those three components, you will have all that you need on your computer to write, run, and test Ruby on Rails Web applications. If you have past experience writing Web applications, you might be thinking that something is missing from that list, some type of HTTP and/or application server. You would be correct in that every Web application needs a server to run; however, the Rails framework includes a server that works very well for developing your applications. The server bundled with Rails is called WEBrick, and it serves as both an HTTP and an application server. This makes it very easy to set up a local development environment without having to install and configure a potentially large and complex server environment.
Sometimes, it's easier to see how the technologies fit together from a visual perspective. Figure QS.1 shows the technology stack that makes up a Web application built with the Rails framework. Each item in the stack has a dependency on what lies beneath it. The middle three layers of the diagram are the three components that you will install software for Rails, Ruby, and the database. ...