C/C++ do use system calls. They also provide and implement an abstraction layer around the OS, more commonly referred to as the CRT (C Runtime) and STL (for C++, Standard Template Library). This abstraction layer is what eases portability, and allows the same source code to compile against and run on different platforms (Windows, MacOS, Linux, etc). The cost (overhead) of this portability is extra code "outside of the concept your program" - this is the "crud" you see when you disassemble a program with GDB or IDA.

In addition to implementing a portability layer, the CRT is also responsible for implementing language features such as static object initialization/deinitialization: think of static C++ objects - who runs their constructors/destructors and when?.

A linker is the tool (final stage of the build process) that combines your program (written by you) with the CRT/STL libraries (written by the compiler authors - Microsoft, GNU/GCC team, etc) into an executable file that one can run.

There are two (complementary, orthogonal) forms of linking: static and dynamic.

Static linking combines the multiple object files together at the time of compilation. If all object files and dependencies in a program are statically linked, then the program is monolithic and has no dependencies.

Dynamic linking decouples and defers linking of certain objects until runtime. This decoupling has two positive effects:

1. performance: code sharing and lower memory footprint - the OS can share the same copy of the CRT+STL for many programs. That is, if you have 10 programs running, all linking with the same CRT+STL, the OS only maintains a single copy of the CRT+STL in memory.
   
2. servicing: an update to the master CRT+STL copy will update all programs using it.
   

There are also negative effects to dynamic linking: missing or mismatched libraries ("DLL hell" in Windows 95/9.

Example of dynamically linked objects are .dll files on Windows, and .so files on Linux/BSD systems.

There are different reasons where one may choose static linking, dynamic linking, or some combination of both.

Hope that helps. Stay safe!

How linkers are working? Is the OS allocating memory on the RAM and loads the CRT to this entry? And when i want to call a CRT function like printf, is my program jumps to this entry?

What is the difference between linked (ELF) and not linked (object file) files? When we compile an application with '-c' tag in GCC, we get an object file as output. When we link a GNU Linker, we get an executable file. What is the difference? I have questions about loaders too but it's out of the concept of this topic.