OS Week 3

• A program is defined as compiled code with four main components: executable format info, text segment, data segment, and BSS segment.
• The executable format info includes lib dependencies, CPE architecture, pointer to entrypoint, and is another file format such as ELF, COFF, or COM.
• The text segment contains compiled machine code and unresolved symbols for loader to resolve against shared libraries.
• The data segment contains initialized global and static variables.
• The BSS segment contains uninitialized global and static variables.
• An instance of a program consists of a program, execution context, address space, stack, heap, and additional OS resources.
• The process control block (PCB) is a kernel structure used to track all of the process state.
• In Linux, the task_struct is used to track process state.
• Context switching changes the entire process, is more expensive than mode switching, and can be initiated in three primary types of context switching: batch, cooperative, and pre-emptive multitasking.
• Batch context switching only happens when process/job terminates.
• Cooperative context switching is when ‘yield’ syscall is made.
• Pre-emptive multitasking involves using a timer interrupt to periodically regain control and a scheduler that tracks how much CPU time a thread has used and picks a different one when the current exceeds its ‘quantum’.
• All faults, traps, and interrupts trigger context switches.
• Three main states for a process & all threads are: Running, Ready, and Blocked.
• Blocking is an important concept as the OS knows it can make no useful progress so it is ineligible to run until it can.
• The main responsibilities of process management include blocking, creating, and destroying.