Components are smallest units of deployment. In java, they are jar files. In ruby, they are gem files and so on. 

This chapter mainly focuses on history of components, how they came into existence in the software world. 

Starting from the earliest – 

1. At first, programmers used to write their programs starting the the physical address where they would be stored in memory. Programs were not relocatable. Programmers would include the source code of library functions with the application code. This resulted in longer load time if programs were big. And eventually this approach failed for very big programs. 
2. Relocatable binaries came next to solve this problem. Compiler was changed to output binaries which included function names as metadata. These binaries also, included the address to be loaded and other flags. All this information was then given to loader. Loader would link the function names to place where it has loaded them. Now, programmers can load only the required functions using loader
3. The above approach worked well for small systems. As the number of libraries increase, the time taken by these linking loaders increased. And so linking and loading were separated. Programmers put the linking part into linker. The output of linker was link relocatable file that a relocating loader can quickly load. But still the loading time couldn’t be reduced. 
4. As storage optimized, disk became short and fast, RAM became fast and efficient, time spent linking and loading application began to shrink too fast. Next came .jar files, and applications where multiple .jar files can be loaded and linked in few seconds. This was era of component plugin architecture. Here, say you want to pin photos on google chrome, just create an extension/plugin and add it to chrome and have it working. 

These dynamically linked files are called the components of our architecture.

Thanks for stopping by! I hope this gives a good preview into components. Eager to hear your thoughts and chat, please leave comments below and we can discuss.