A Gentle introduction

ROOT is a framework for data processing, born at CERN, at the heart of the research on high-energy physics.  Every day, thousands of physicists use ROOT applications to analyze their data or to perform simulations.  If you have never heard about ROOT before, this introduction should provide you a broad overview of its capabilities.  To make a tour through the framework, we will assume that you are collecting data from some source and need to store them, in order to be able to process them and show your results in some graphical form.  In the following, few sections will guide you through the following items:

• Save data.  You can save your data (and any C++ object) in a compressed binary form in a ROOT file.  The object format is also saved in the same file.  ROOT provides a data structure that is extremely powerful for fast access of huge amounts of data - orders of magnitude faster than accessing a normal file.
• Access data.  Data saved into one or several ROOT files can be accessed from your PC, from the web and from large-scale file delivery systems used e.g. in the GRID.  ROOT trees spread over several files can be chained and accessed as a unique object, allowing for loops over huge amounts of data.
• Process data.  Powerful mathematical and statistical tools are provided to operate on your data.  The full power of a C++ application and of parallel processing is available for any kind of data manipulation.  Data can also be generated following any statistical distribution, making it possible to simulate complex systems.
• Show results.  Results are best shown with histograms, scatter plots, fitting functions, etc.  ROOT graphics may be adjusted real-time by few mouse clicks.  High-quality plots can be saved in PDF or other format.
• Interactive or built application.  You can use the CINT C++ interpreter or Python for your interactive sessions and to write macros, or compile your program to run at full speed. In both cases, you can also create a graphical user interface.