Assembler is a system program that converts a program written in assembly language into machine language.
• An input to an assembler is an assembly language program.
• The output from the assembler is a machine code known as object program.
A program may consist of one or more subroutines. All these sub routines must be linked together to execute a program.
Linker is a system program that is used to combine the individual object modules into one single executable program.
• A linker combines all the modules into a single program so that the program can be executed.
• It loads the program into memory and starts the execution.
Assembler converts assembly language program into machine language. While Linker links the object modules into single executable program and start execution. Hence the assembler and linker are needed to work together to execute a program.