An assembler is a program that converts assembly language into machine code. It takes the basic commands and operations from assembly code and converts them into binary code that can be recognized by a specific type of processor.
Assemblers are similar to compilers in that they produce executable code. However, assemblers are more simplistic since they only convert low-level code (assembly language) to machine code. Since each assembly language is designed for a specific processor, assembling a program is performed using a simple one-to-one mapping from assembly code to machine code. Compilers, on the other hand, must convert generic high-level source code into machine code for a specific processor.
Most programs are written in high-level programming languages and are compiled directly to machine code using a compiler. However, in some cases, assembly code may be used to customize functions and ensure they perform in a specific way. Therefore, IDEs often include assemblers so they can build programs from both high and low-level languages.