Honestly, I don't know if this is the right place to ask a question like this but at least it's worth the try.

I've been wondering about this: When write your code and declare your functions and variables, obviously you refer to them by their name so the machine does exactly which one are you about to access or execute or so, but after compilation does your variable/function names "disappear" and be replaced by an offset address in the compled exe, dll ? Also your executable is loaded to a different part or the memory so their physical address can be very different every time you load your exe, and I suppose that the function addresses are resolved using the address of the first byte of the executable, and the adding the offset, is that correct, at all? Besides that, what happens exactly when your memory is fragmented, and say you don't have a single block of continuous memory where you can "fit" your executable into, does the executable become fragmented as well?

If yes, how does the computer resolve function and/or variable addresses, since addig the offset will not give the correct address, it has to keep track of the fragments as well.

If no, then it can't execute your program at all, right?

I'd be happy if someone knows the answer, because I'm very curious about this.

Thx

Many things in memory, after being converted from code to an EXE, doesn't always exactly lose its names. They become translated into a context that assembly understands. For example an If statement or nest could be translated into a pattern of short jumps and long jumps in assembly and your integers are kept as register values. Everything is there but in another readable language.

When things jump around they either know the address to jump to, or like you said, jump a certain amount of spaces from where it already is as an offset.

Yes. Names are high level concepts. Just like what a programming language is in the first place. It's a bridge between programmers and computers. Neither humans and computers directly know it. Humans expend time learning this language. For computers, a set of more programs convert that code in that language to something that the operating system and the processor understand.

Processors don't deal with names.

It's more complicated, so neither a yes nor no answer makes sense. It's also OS and architecture dependent, actually. The best way to really understand these details is to look at the resources involved in learning Assembly (probably x86 assembly, Windows OS, for you), not because Assembly is the enlightening answer, but because at that limited level of abstraction, you are exposed to the relevant information.

Again OS dependent. And part of learning Assembly or OS design is that you understand common strategies for memory handling. Overall, what you'll learn is that, yes, in physical memory, the program is commonly spread out in fragments.

By doing additional bookkeeping. That expensive OS you buy has a system of managing memory. There's several abstractions going on here. There's what memory looks like in say, C, C++, Python, etc.. Then there's memory according to how the OS presents to various programs. And then there's physical memory. The OS will manage physical memory, and present it in a uniform manner to programs. In fact, your processor does some additional memory management too (caching).

I know the answer isn't useful, but this is a question that's resolved in a single forum post. You'll have to delve into books and a good bit of technical reading to really understand all that's going on behind the scenes.

great coverage by Oler1s.

thought I would drop you a link for further clarification on Operating System memory management.

Page Tables

It's a complicated topic and can take a while to get your head around it. Fortunately unless your using a low level language, you won't need to know too much about it. This article can give you a quick look at the guts of it along from one implementations perspective. Other implementations are going to be similar.


Aet

This post has been edited by Aeternalis: 4 Sep, 2009 - 03:01 PM

Wow! very good posts.
Thank you very much for your help

You have to know about the working real mode and protected mode to get your answer and Yes the names of the variables are converted into file offset in the exe file and when you executes it the OS maps(called mapping)the file in memory(RAM) and assign the physical address of every data.At right this moment it is a little hard to understand for you about this.First learn about real mode and protected mode operation and offcourse about PE file structure (.Exe) and more important is Assaembly you will get all your answer.

Good Luck

This post has been edited by debjit625: 6 Sep, 2009 - 04:05 AM