I often point out to clients during training the amount of code that goes into building the Magento platform. I do this not to intimidate those in attendance but to communicate the enormity of what goes into the Magento platform and to help them understand why custom Magento development can be complicated, time consuming and expensive.
Obviously, Magento comes with a ton of functionality out-of-the-box. As far as available eCommerce platforms, it comes with a wealth of features (see a full listing of Magento features here). This functionality is possible because of the various codes used to make the platform.
With over 13 million total lines, over 8 million are code, and 11 different languages used, Magento is big, very BIG.
Here is a quick breakdown of the codes that go into making this platform.