A machine language defines a set of instructions that a CPU can execute to perform operations. In other words, a machine language defines what you can do with your computer. Modern processors have very complex instruction sets; however, the simple language described here can give you an understanding of what is happening "under the hood" with your computer.  Machine language is the actual data that is directly run by the processor. Writing a program in machine language can therefore be advantageous if you need to save space or highly optimize your code. However, machine language is also not portable and can be difficult to understand and maintain.  Therefore, almost all code is now written in a higher level language, such as C, C++, Java, or scripting languages such as shell or perl. These languages all have their advantages and disadvantages as well, such as varying levels of portability, maintainability, scalability, and execution speed.  One level higher than machine language is assembly language. Assembly language is basically readable machine language. Instead of writing out the code bit-by-bit, you write out the code as a sequence of human readable instructions, which are then compiled almost directly into machine language.