Imagine the next situation: you were coding some It-can-do-anything super function for a few days and just as you thought it is now finished your fellow Delphi programmer tells you that you have wasted your time: Delphi has that function built in. Aarhg!
Delphi Run Time Library
The raw power of Delphi is based on a considerable amount of its Run Time Library (RTL) functions and procedures. Run Time Library, or VCL routines are functions and procedure that are built into Delphi. RTL represents code that is essential to any application that we can built with Delphi. Most of RTL function and procedures are defined in the System and SysUtils unit. Both units are automatically included in every Delphi unit.
Since the RTL routines are all written in Delphi (with the help of assembler), this collection of source files makes for an excellent educational resource. To open up either of these units in the code editor in Delphi find a reference to them (e.g. in a uses clause), right-click and choose Find Declaration.
About Delphi Programming site provides a through example-reference to the RTL capabilities of Delphi. Every routine is presented with a routine header and is described in a few to-the-point words, with sample code plus a link to some "real code" article.
Browse Delphi's RTL Examples