CHAPTER 2  The Concept of Data:  Simple Data Types  Data  is the general term describing all that is operated on by a computer.  At the hardware and machine-code levels, all data are represented as  sequences of binary digits (bits). Higher-level languages allow the use  of abstractions  that  ignore  the  details  of representation  - by  developing the  data type  concept.  A data type defines the set of values a variable may assume and the  operations which may be applied to it. Every variable occurring in a  program is associated with one and only one type. Although data types  in Pascal can be quite sophisticated, each must be ultimately built from  unstructured, simple types.  Pascal also provides facilities for creating collections of data types  in the form of structured types and pointer types. These types are  described in Chapters 6 through 10.  Figure  2.a  Type taxonomy of data types  [llita Types  Simpl'  ~"  p~,,,  TypO'  Structured Data Types  14 