Dependency of a C program on CPU and OS

1
votes

Let's think about a simple C program compiled in Windows.

  1. I can compile the program on an Intel CPU machine and run it on an AMD CPU one (same operating system). So does it mean that the instruction set of the CPU's are the same?

  2. Why doesn't the same program run on a machine with different OS and the same CPU?

3
operating-systemdependenciescpu
Regarding 2), see the answers to stackoverflow.com/questions/1442921/… - Pascal Cuoq

3 Answers

3
votes

Intel and AMD line of processors in general have a big overlap in the instruction set that they implement (e.g. sometimes one the other invent some new things and there is a gap until the other company catches up) - that is why you can run programs on both architectures. The same is the reason you cannot run it on other CPU architectures - they don't have the same instruction set for starters, but there are many things that are different.

Operating systems also have their differences. For example, when you compile a program under Windows, you generally get an .exe file. That .exe has a format that only Windows understands and is very different from the format used by Linux for example.

Also, the support that OS gives is completely different - Windows has different kernel functions that you can call compared to e.g. OpenBSD. Even on more abstract levels, it's incompatible. E.g. Windows uses drive letters such as C:\, D:\ and so on to mark drives, while e.g. under Linux it's one big filesystem where you mount different partitions, e.g. under /media or so.

There are different attempts, such as Wine and Cygwin, to execute programs from one platform on another. Using Wine, you can execute Windows executables on Linux directly, as it tries to emulate what Windows provides (not everything works, though). Cygwin is a different product - you can run Windows programs that work similarly to GNU programs on Linux, but they need to be specially compiled - just giving you a hint that it's just two worlds.

That is why Java and .NET (with Mono support on Linux) try to bring these two together. When you make a Java application, you should be able to run it on Linux with more or less same code - some things might not be the same, but majority is.

0
votes

They're the same, or at least your program is using only a common subset.

For your second question, a few common reasons include:

  1. different OSes require different formats of executables
  2. different OSes will typically have different functions for the program to use
  3. different OSes use different ways of invoking what they provide
0
votes

1) Intel CPUs and AMD CPUs are intentionally produced this way. You can not run a program compiled for, say, SPARC CPU on, say, an ARM CPU.

2) In theory it can. Say, Linux has this Wine thing to emulate Windows. Many Windows programs run perfectly on Linux under Wine.