chapter 2 - os structure

Question 1

System Calls are

Answer 1

programming interface to the services provided by the OS

Question 2

System Calls are accessed

Answer 2

by programs via a high-level api

Question 3

Methods of passing parameters to OS

Answer 3

1. pass the parameters into the registers
2. Store parameters in a block, table, or memory and the address of each block is passed into the register
3. parameters are pushed onto the stack by a program and then popped off by the OS

Question 4

Process Control is an OS service that

Answer 4

• Creates, terminates, ends, and aborts processes
• Loads and executes, gets and sets attributes
• Allocates and frees memory, dumps and debugs

Question 5

File Managements is an OS service that

Answer 5

• Create, delete, open, close, get and set file attributes

Question 6

Device Management is an OS service that

Answer 6

• request, release, reads, writes, and get/set device attributes
• logically attaches and detaches devices

Question 7

Information Maintenance is an OS service that

Answer 7

• get/set time or date, system data, process, file or device attributes

Question 8

Communications is an OS service that

Answer 8

• Create, and delete communication connection
• Send, and receive messages if the message passing model to hostname or process name
• shared-memory model create and gain access to memory regions
• attach and detach remote devices

Question 9

Protection is an OS service that

Answer 9

• controls access to resources
• get and set permissions
• allow and deny user access

Question 10

User mode processes:

Answer 10

executes on behalf of the user

Question 11

Kernel mode processes:

Answer 11

executes on behalf of the kernel

Question 12

Mode bit:

Answer 12

a bit in the hardware to switch between modes

Question 13

Transitioning between User/Kernel mode

Answer 13

1. user code calls a system call
2. OS checks that everything is in order and legal then switch
3. OS executes system call which may contain multiple privileged instructions
4. mode again set to user mode

Question 14

What does ‘su’ command perform

Answer 14

switch to super user account

Question 15

what does ‘sudo’ do

Answer 15

run program on behalf of the superuser
(doesn’t necessarily switch to the kernel mode)

Question 16

what does strace -c ls do

Answer 16

displays summary info on system calls invoked during the execution of the command ‘ls’

Question 17

Changing the mode bit of the CPU ___ can only be done by a privileged instruction

Answer 17

from user mode to kernel mode

Question 18

A supervisor (kernel call) is

Answer 18

• a privileged instruction that automatically transfers execution control to a well-defined location within the OS kernel
• the supervisor calls provide the interface between the OS kernel and the higher level software

Question 19

T/F: A system call is a kernel function

Answer 19

False

Question 20

MS-DOS

Answer 20

• written to provide the most functionality in the least space
• not divided into modules
• its interfaces and levels of functionality are not well seperated

Question 21

Monolithic

Answer 21

• no structure, entire kernel is in a single binary file
• is high performance, with little overhead in the system call interface and fast communication
• difficult to implement and maintain

Question 22

Layered Approach

Answer 22

• The operating system is divided into a number of layers, each built on top of lower layers
• the bottom layer is the hardware, and the highest is the UI
• easy to develop, debug and update
• less efficient, tricky to define layers