What happens when a program executes - from source code to hardware?

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Welcome! Today we'll explore what happens when a program executes - the incredible journey from source code to hardware. When you write a program and hit run, your computer performs a complex series of transformations to convert your human-readable code into instructions that the hardware can understand and execute. There are two main approaches to transform source code into executable instructions. Compilation translates the entire program into machine code before execution, creating an executable file. Languages like C and C++ use this approach. Interpretation, on the other hand, reads and executes the source code line by line at runtime. Languages like Python and JavaScript use interpreters that translate each instruction as the program runs. Once we have an executable program, it needs to be loaded into memory before it can run. The operating system's loader is responsible for this crucial step. It reads the executable file from storage, such as a hard drive, allocates the necessary memory space in RAM, and loads the program code and data into memory. The loader also sets up the execution environment, organizing memory into sections for program code, variables, and the execution stack. Now the CPU can begin executing the program using its fundamental three-step cycle. First, it fetches the next instruction from memory. Then it decodes the instruction to understand what operation needs to be performed. Finally, it executes the instruction, which might involve arithmetic operations, data movement, or control flow changes. This fetch-decode-execute cycle repeats continuously, with the CPU processing millions or billions of instructions per second, until the program completes. During program execution, the CPU constantly interacts with various hardware components to complete its tasks. It reads and writes data to memory, receives input from devices like keyboards and mice, sends output to screens and speakers, accesses files from storage devices, and communicates over network interfaces. This intricate dance between software and hardware is what makes modern computing possible. From the moment you write source code to when it executes on the hardware, your program has traveled through compilation or interpretation, loading into memory, and finally execution with full hardware interaction. This remarkable process happens millions of times per second in modern computers!