Explanation
Kernel
Kernels directly manage hardware resources (CPU, memory, files, devices) and are written mostly in C (~95%) with some assembly language (~5%) for low-level operations. The kernel source code gets compiled into machine language that the CPU executes. The final kernel runs as pre-compiled machine code, never needing runtime compilation.
For new hardware, kernels are ported by rewriting only the assembly code (~5%) and architecture-specific C code (~10-15%). The majority of C code (~80-90%) remains portable across different architectures.
System Calls
User programs can’t directly access hardware, so system calls act as an interface which allows user programs to request service from the kernel
If we think of the computer as a restaurant, we won’t tell the chef (kernel) directly what we want to eat. Instead, we’ll order our food from the counter (system calls)
Shell
Shell is command-line interface that acts as the bridge between you and system calls
Library Routines
Library routines are the pre-written functions that provide a layer between programs and system calls
Applications
The programs that we use in daily life