System programs provide an environment where programs can be developed and executed. In the simplest sense, system programs also provide a bridge between the user interface and system calls. In reality, they are much more complex. For example: A compiler is a complex system program.
The user view of the system is actually defined by system programs and not system calls because that is what they interact with and system programs are closer to the user interface.
An image that describes system programs in the operating system hierarchy is as follows:
In the above image, system programs as well as application programs form bridge between the user interface and the system calls. So, from the user view the operating system observed is actually the system programs and not the system calls.
System programs can be divided into seven parts. These are given as follows:
These system programs are used to manipulate system files. This can be done using various commands like create, delete, copy, rename, print etc. These commands can create files, delete files, copy the contents of one file into another, rename files, print them etc.
The status information system programs provide required data on the current or past status of the system. This may include the system date, system time, available memory in system, disk space, logged in users etc.
System programs that are used for file modification basically change the data in the file or modify it in some other way. Text editors are a big example of file modification system programs.
These system programs provide additional support features for different programming languages. Some examples of these are compilers, debuggers etc. These compile a program and make sure it is error free respectively.
The system programs that deal with program loading and execution make sure that programs can be loaded into memory and executed correctly. Loaders and Linkers are a prime example of this type of system programs.
These system programs are needed for system communications such as web browsers. Web browsers allow systems to communicate and access information from the network as required.
Application programs can perform a wide range of services as per the needs of the users. These include programs for database systems, word processors, plotting tools, spreadsheets, games, scientific applications etc.