While I am taking the online course, I realize it would be more helpful to write a blog post for better understanding on the concept.
What is a process?
Process is an active instance of a program that is launched in the memory.
What information does a process contain? What does it look like?
A process holds its code (.text), variables (.data), dynamically created objects (.heap), and variables & function calls (stack). Variables stored in stack and .data are different.
![description of a process](/_next/image?url=%2Fcontent%2Fprocess.png&w=640&q=75)
What is the address space of a process?
Even though a process is located in memory, it uses virtual address space. Using a virtual address helps OS to manage physical memory space, access authorization to memory, and more.
'&' in C language shows a virtual address. Even when two virtual addresses are contiguous, their physical addresses do not have to be.
Context Switch
When creating a new process, OS also creates PCB (process control block). It contains information about program counter, CPU register values, and so on.
While single CPU can only run a single process, it constantly switches between processes in order to give a better experience. When a process is idle, OS will schedule a CPU to run another process. It is called context switch.
However, it is an expensive computation because it requires to load and change all information from memory and causes cold cache.
Process Creation
In most cases, processes are managed by tree-like structure in OS to keep track of all of them. There is a root process that creates child processes.
When creating a new process, parent process can either fork or exec. Fork will copy the parent PCB to a new process. Exec will create a new process with new PCB.