Module 2

Question 1

Kernel

Answer 1

one of two core components of OSs (with the file system).

Question 2

File management system

Answer 2

one of two core components of OSs (with the
kernel). 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

the 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.

Question 5

User mode

Answer 5

applications in user mode can only run instructions that affect its 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.

Question 7

Privileged machine instruction

Answer 7

have global effects on your whole computer and external devices. Examples include (1) writing data to disks and (2) 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 model for processes. Each process has its own address space of five segments, including (1) Code, (2) Data, (3) Heap, (4) Stack, and (5) Kernel space.

Question 12

Code

Answer 12

a segment of the process address space that is, by convention, 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. It points to the address of the next instruction to execute in the Code segment.

Question 14

Data

Answer 14

​a segment of the process address space that, by convention, is stored in the memory locations just above the Code segment. Stores statically-defined variables.

Question 15

Heap

Answer 15

​ a segment of the process address space that, by convention, is stored in the memory locations just above the Data segment. Stores dynamically allocated memory. Grows and shrinks at runtime during program execution, for example using malloc() and free() system calls in C.

Question 16

Stack

Answer 16

a segment of the process address space that, by convention, is stored in the memory locations just above the Heap segment. Stores temporary values required during function calls and pops them off once the function completes.

Question 17

Kernel space

Answer 17

a segment of the process address space that, by convention, is stored in the memory locations 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 (PCB)

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

processes are managed in a hierarchical structure. A parent process creates child processes.

Question 23

PPID

Answer 23

PID of the process’s parent.

Question 24

File descriptors

Answer 24

handles to open files used by processes.

Question 25

Copy on write

Answer 25

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 26

Fork()

Answer 26

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 27

Exec()

Answer 27

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

Question 28

Wait()

Answer 28

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

Question 29

Exit()

Answer 29

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

Question 30

Process state

Answer 30

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

Question 31

Signals

Answer 31

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 32

Superuser

Answer 32

an account with special permissions on a machine. The exact permissions vary depending on the machine’s OS.

Question 33

Orphan process

Answer 33

process A is an orphan process if process A is the child of process B, B has terminated, but A is still running.

Question 34

Zombie process ​process

Answer 34

​process A is a zombie process if process A is the child of process B, but B has not called wait on A.

Question 35

Daemon process

Answer 35

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

Question 36

Shell

Answer 36

an interface allowing the user to enter OS commands.