To understand Hotwire, we first need to know how a typical request-response cycle works when a browser requests a web page.

When you go to a website in the browser or click a link on a page, it makes a GET request to the server, which sends an HTML response to the requesting browser. The browser then parses the HTML and displays the web page.

The advantage of this simple architecture is that most of the application logic stays on the backend, where you’re free to choose any language you like, such as Ruby, PHP, or even JavaScript.

When you need some client-side interactivity, you sprinkle some JavaScript (or use JQuery) to get the job done. The pages load much faster, as the browser only has to render an HTML response without loading and parsing big JavaScript frameworks.

However, a disadvantage of traditional web applications is that the browser reloads the whole page when you click a link, throwing away the existing HTML. It also fetches the assets listed in the HTML, such as JavaScript, CSS, and images, even if they haven't changed.

Now, these assets are cached on the browser most of the time, which makes this process relatively fast, but the basic idea remains the same. The browser has to parse and interpret the whole HTML again. So the web application doesn’t get a native application-like feeling. It still feels like a website.

This was the original web architecture (that made the web popular and successful), and many web applications still work that way. However, with advances in browsers, a new category of web applications became popular in the last ten years, known as Single-Page Applications, or SPAs for short.