chapter 4: the abstraction: the Process

Question 1

what is a process?

Answer 1

a running program

Question 2

what is Time Sharing and Space Sharing?

Answer 2

sharing time and space between programs (only one or a few CPU and only one big address space

Question 3

what are the steps an OS has to do to run a program?

Answer 3

1. load its code and static data into memory, the address space of the process
2. programs initially reside on disk, SSDs in some kind of executable format.
3. OS reads those bytes from disk and place them in memory somewhere
4. memory allocated for the programs runtime stack. (local variables, function parameters, return addresses.
5. the OS fill in the parameters to main() and initialze the stack.
6. the OS allocate memory for program’s heap. (malloc() , free()). heap will be small at first, OS may get involved and add more memory if needed.
7. OS sets up I/O
8. start the program main() by jumping to the main() routine. Transfers control of CPU to process

Question 4

how was loading process done in OS before?

Answer 4

it was loaded EAGERLY, all at once before running the program. now its done LAZILY, only loading it when needed.

Question 5

Process states

Answer 5

running, ready, blocked

Question 6

how do the states change from one another

Answer 6

running to ready: descheduled
ready to running: scheduled
Blocked to ready: I/O done
running to blocked: I/O initiate

Question 7

data structures of a process

Answer 7

the OS keeps a process list: to track states of all processes
each process has a PCB: contains information of a process (stack pointer, PID, process state, parent process etc)