Module 2: OS Overview

Question 1

kernel

Answer 1

one of two core components (with the file system)

Question 2

file management system

Answer 2

one of three core components of OSs (with kernel and I/O component). all data in a computer is stored in the form of a file, and the OS helps maintain the file sizes, names, locations, directory structures, and file access rights

Question 3

CPU

Answer 3

computer processing unit; circuitry to execute program instructions

Question 4

CPU cycle

Answer 4

the cycle performed by the CPU to read a program instruction, execute it, and repeat it

Question 5

user mode

Answer 5

applications in user mode can only run instructions that affect is own application; executing functions in the application’s code

Question 6

kernel mode

Answer 6

allows privileged machine instructions to run. this mode is entered by flipping a bit on the CPU (TRAP)

Question 7

privileged machine instructions

Answer 7

have global effects on your whole computer and external devices. examples: writing data to disks and running the logic that makes one application stop running, and instead start running another application

Question 8

process

Answer 8

a program in execution. because there are limited CPU cycles and the OS needs to perform many tasks, the process concept allows OSs to switch between executing different tasks

Question 9

process context

Answer 9

the snapshotted state of a process, which includes its data, memory utilization, and execution progress. the process context must be saved when the OS wants to stop running a process, and it gets reloaded when the OS resumes running the process

Question 10

process management

Answer 10

a function of the OS kernel that manages applications using an abstraction called a process

Question 11

address space

Answer 11

the memory organization for processes. each process has its own address space of five segments:

1. code
2. data
3. heap
4. stack
5. kernel

Question 12

code

Answer 12

segment of the process address space that is stored in the memory locations specified by the lowest addresses. consists of the instructions being executed for the process

Question 13

program counter

Answer 13

register value stored in the CPU. points to the address of the next instruction to execute in the code segment

Question 14

data

Answer 14

segment of the process address space that is stored in the memory locations just above the code segment. stores statically-defined variables

Question 15

heap

Answer 15

segment of the process address space that is stored in the memory locations just above the data segment. stores dynamically allocated memory. grows and shrinks at runtime during program execution (malloc and free)

Question 16

stack

Answer 16

stored just above heap segment. stores temporary values required during function calls and pops them off once the function completes

Question 17

kernel space

Answer 17

stored just above the stack segment. reserved space for the OS and privileged code

Question 18

process identification number (pid)

Answer 18

unique number assigned to each process by the OS

Question 19

process table

Answer 19

contains an array of process control blocks and is maintained by the OS

Question 20

process control block

Answer 20

each PCB stores the context of a single process

Question 21

init process

Answer 21

the only process that exists when the OS is booted. all other processes are child processes of init

Question 22

parent and child processes

Answer 22

hierarchical structure / parent creates child

Question 23

PPID

Answer 23

PID of the process’ parent

Question 24

copy-on-write

Answer 24

on the creation of a new process, the child shares the parent’s memory address space until a modification is required. on a modification, a distinct memory page is then created for the child

Question 25

fork()

Answer 25

system call that creates a new process and gives an integer return value, which is used to differentiate between the child and parent processes that are simultaneously running the same code after the call

Question 26

exec()

Answer 26

accepts a path name to a code file as an input and allows the child to execute this new piece of code

Question 27

wait()

Answer 27

allows a process to wait for another process to finish completing, to give a signal, or to perform some other specified condition; settings are specified in the Linux man-pages

Question 28

exit()

Answer 28

terminates the process in which the exit() command is invoked

Question 29

process state

Answer 29

running: instructions for this process are being executed by the CPU
blocked: process is waiting on I/O to access, user input, or some other condition required to continue executing
ready: the process that has all it needs to run and is waiting for CPU access

Question 30

signals

Answer 30

software interrupts sent from process A to process B to communicate an event that took place in process A. Process B can be set up to watch for certain signals and respond accordingly, depending on the application being run

Question 31

superuser

Answer 31

an account with special permissions on a machine. the exact permissions depend on one’s OS

Question 32

orphan process

Answer 32

a child whose parent process has been terminated but it (the child process) is still running

Question 33

zombie process

Answer 33

if a child’s parent process has not called wait on it

Question 34

daemon process

Answer 34

system-level processes that are started to run OS-specific management tasks

Question 35

shell

Answer 35

an interface allowing the user to enter OS commands