The BIOS that runs in your computer on power up is executable code stored in ROM. It consists of machine instructions plus data. There is a compiler that assembles this BIOS from source code. This is a special case.

In the general case, it is much more practical to have the compiler produce some instructions that invoke system services provided by a kernel or a library. It makes the compiler much more lightweight. It also makes the compiled code more lightweight.

The BIOS that runs in your computer on power up is executable code stored in ROM. It consists of machine instructions plus data. There is a compiler (or assembler) that assembles this BIOS from source code. This is a special case.

Other special cases include the bootstrap program that loads the kernel and the kernel itself. These special cases are generally coded in a language other than C++.

In the general case, it is much more practical to have the compiler produce some instructions that invoke system services provided by a kernel or by library routines. It makes the compiler much more lightweight. It also makes the compiled code more lightweight.

At the other end of the spectrum is Java. In Java, the compiler does not translate the source code into machine instructions, as this term is usually understood. Instead, the source code is translated into "machine instructions" for an imaginary machine, called the Java Virtual Machine. Before a Java program can run, it must be combined with the Java runtime, which includes an interpreter for the Java Virtual Machine.