What is the difference between SAP Basis and SAP ABAP?

BASIS is like an Operating System for R/3. We can say that BASIS is a middleware between ABAP/4 (Advanced Business Application Programming) and the computer Operating system. R/2 system was mainframe based. SAP ported it to client/server environment. To do this SAP created BASIS. Creating BASIS enabled ABAP/4 code to run on other platforms as well. ABAP/4 programs cannot run directly on an Operating system (like Windows). It requires set of programs (collectively known as BASIS) to load and intreprete its input and output. Without BASIS programs ABAP/4 programs cannot run. You can relate BASIS to ABAP/4 programs, like Windows is to Windows programs. To install BASIS, the installer runs the program "r3inst" at the command prompt level of O/s. Like most installs, this also creates a directory structure and copies set of executables into it (like for e.g. when we install the Windows operating system in our computer, it creates a directory structure like program files, windows etc..and copies set of executables into it). These executables taken together form BASIS. Thus, ABAP/4 programs run within the protective BASIS environment. They are not executables that run on an Operating system. Instead BASIS reads ABAP/4 code and intrepretes it into Operating system instructions. ABAP/4 programs do not access O/S functions directly. Instead they use the BASIS function to perform the file input/output operation and display data in windows. read less