Bulldozer00's Blog

Someone asked on Twitter what a “native” app was. I answered with:

“There is no virtual machine or interpreter that a native app runs on. The code compiles directly into machine code.”

I subsequently drew up this little reference diagram that I’d like to share:

Given the source code for an application written in a native programming language, before you can run it, you must first compile the text into an executable image of raw machine instructions that your “native” device processor(s) know how to execute. After the compilation is complete, you command the operating system to load and run the application program image.

Given the source code for an application written in a “managed” programming language, you must also run the text through a compiler before launching it. However, instead of producing raw machine instructions, the compiler produces an intermediate image comprised of byte code instructions targeted for an abstract, hardware-independent, “virtual” machine. To launch the program, you must command the operating system to load/run the virtual machine image, and you must also command the virtual machine to load/run the byte code image that embodies the application functionality. During runtime, the virtual machine translates the byte code into instructions native to your particular device’s processor(s).

Given the source code for an application written in an “interpreted” programming language, you don’t need to pass it through a compiler before running it. Instead, you must command the operating system to load/run the interpreter, and you must also command the interpreter to load/run the text files that represent the application.

In general, moving from left to right in the above diagram, program execution speed decreases and program memory footprint increases for the different types of applications. A native program does not require a virtual machine or interpreter to be running and “managing” it while it is performing its duty. The tradeoff is that development convenience/productivity generally increases as you move from left to right. For interpreted programs, there is no need for any pre-execution compile step at all. For virtual machine based programs, even though a compile step is required prior to running the program, compilation times for large programs are usually much faster than for equivalent native programs.

Based on what I know, I think that pretty much sums up the differences between native, managed, and interpreted programs. Did I get it right?