Operating system organization (week 2)

Question 1

what does an operating system provide

Answer 1

provides an environment for the safe and secure execution of application programs while doing it in an efficient and fast manner.

Question 2

operating systems are organized along 2 different lines which are ?

Answer 2

–> those that provide convenience for the user/program
–> those that ensure efficient operations of the system

Question 3

what are the 6 services that provide convenience for user/program

Answer 3

–> user interface (Batch interface, CLI, GUI)
–> program execution (load, run & terminate the program)
–> Input/Output operation (file, cd/DVD, smartcard)
–> File system manipulation (create, read, write files and permission management)
–> Communications (Local/remote inter-process communication)
–> Error detection (able to detect error and take proper action)

Question 4

what are the 3 services that provide

Answer 4

–> Resource allocation
–> Accounting
–> Protection and security

Question 5

what is resource allocation

Answer 5

–> Resources to be allocated among multiple users fairly
–> Different algorithms are used to properly allocate different resources

Question 6

what is accounting

Answer 6

–> Keep track of usage statistics eg CPU, Printer, Harddisk quota
–> Reconfigure system to improve computing services

Question 7

what is protection and security

Answer 7

–> security of the system from outsiders
–> ensures that access to all system resources is controlled
–> audit trail must also exist so that people can find out what happened

Question 8

what are the 4 core functions of the OS

Answer 8

–> device management
–> process, thread, and resource management
–> memory management
–> file management

Question 9

Based on the four functions (device management, process, thread and resource management, memory management, and memory management ), the modern OS
implements________, which provides
__________ to the respective resource that they
manage.

Answer 9

4 major managers

abstractions

Question 10

there is ___________ interaction between the 4 major managemers

Answer 10

close

Question 11

what is device management?

Answer 11

–> it refers to the way the generic devices are handled
–> special management approaches for processor and memory
–> partitioning design simplifies adding and upgrading devices

Question 12

what is process, thread and resource management

Answer 12

–> creates abstractions of processes, threads, and resources.
–> allocates processor resources equitably
–> allocates and tracks abstract resources such as queues, semaphores, and messages.
–> cooperates with the memory manager to administer the primary memory

Question 13

what is memory management

Answer 13

–> administer and allocate primary memory
–> enforces resource isolation
–> enables sharing between processes
–> provides virtual memory extensions (abstract machine’s memory appears larger than physical memory)

Question 14

what is memory management?

Answer 14

–> administer and allocate primary memory
–> enforces resource isolation
–> enables sharing between processes
–> provides virtual memory extensions (abstract machine’s memory appears larger than physical memory)

Question 15

what is file management

Answer 15

–> creates abstractions of storage devices
–> range from byte stream files to indexed records
–> file system should also allow users to access local and remote files over the internet

Question 16

how does OS manage resource sharing

Answer 16

–> time/space multiplex sharing (use this where appropriate)

–> Exclusive use of a resource (Allow processes to use a resource exclusively as required.)

–> Isolation (Allow a resource to save information without fear of it being modified or tampered with.)

–> managed sharing (sharing must be done in an orderly fashion according to the properties of the resource)

Question 17

what are the 3 mechanisms to address isolation and sharing

Answer 17

–> processor modes
–> kernels
–> method of invoking system service

Question 18

what are processor modes

Answer 18

–> processor modes help to distinguish between trusted and untrusted software
–> Determine execution capability and accessible
memory areas

Question 19

what are 2 modes that modern processors provide

Answer 19

supervisor mode
user mode

Question 20

what is supervisor mode (for OS)

Answer 20

–> it can execute all machine instructions
–> can reference all memory locations

Question 21

what is user mode (for user programs)

Answer 21

–> can execute a subset of instructions
–> Can only reference a subset of memory locations

Question 22

The processor in supervisor mode can execute all
instructions including __________ instructions

Answer 22

privileged

Question 23

privileged instructions are also called ?

Answer 23

supervisor/protected instructions

Question 24

Examples of privileged instructions are ?

Answer 24

–> I/O instructions
–> Memory-related instructions
–> Processor mode-change instructions

Question 25

Processor in user mode can execute only __________ instructions.

Answer 25

nonprivileged

Question 26

Processor in supervisor mode can access ______ and _______ memory locations

Answer 26

system and user space

Question 27

what is system space

Answer 27

refers to the memory area used by the OS

Question 28

what is user space

Answer 28

refers to the memory area used by application processes

Question 29

processor in user mode can only access ______

Answer 29

user space

Question 30

trusted os software executes in the ______

Answer 30

supervisor mode

Question 31

All other software (including some parts of the OS) executes in __________

Answer 31

user mode

Question 32

what is concept

Answer 32

allows for OS to be able to control access to resources

Question 33

how does concept work

Answer 33

--> User programs have to ask the OS to execute privileged instructions on their behalf. --> Any particular configuration can isolate or permit sharing or resources according to the administrator’s policy

Question 34

what is a kernel

Answer 34

--> part of the OS critical to correct operation (trusted software)

Question 35

how does a kernel work?

Answer 35

--> Implements the basic mechanisms that assure secure operation of the entire OS --> Executes in supervisor mode --> The trap instruction is used to switch from user to supervisor mode, entering the OS

Question 36

what is a trap table

Answer 36

--> a reference table --> user program will get permission from the kernel and indicate which trap instruction is needed to execute

Question 37

what are routines

Answer 37

In order to execute privileged instructions, user programs have to activate routines in the kernel, which can then execute on the user programs’ behalf.

Question 38

what are 2 techniques to request services from os

Answer 38

system call message passing

Question 39

what is a system call

Answer 39

--> In a system call, the relevant function is activated via a trap instruction. --> OS provides a stub function which the user program calls --> Stub function will switch the processor to the supervisor mode --> It will execute the trap instruction by branching to a trap table to the entry point of the system function to be invoked --> On completion, processor is switched back to user mode and control returns to user process --> Appears as ordinary function call to the application programmer

Question 40

what is message passing

Answer 40

--> In the message passing method, the user program constructs a message that requests the desired service. --> Uses OS send() system call --> OS kernel implements target function --> Kernel process must be started or active i.e. must be in supervisor mode, to receive message --> User process waits for result with receive() operation --> Kernel sends message back to user process on completion

Question 41

In system call, the user process/thread gains ability to execute ____________

Answer 41

privileged instructions

Question 42

In the message-passing method, the system function is executed by the ________

Answer 42

kernel process/thread

Question 43

why are System calls more efficient than message passing.

Answer 43

--> Message passing has cost of message formation/copying and process multiplexing --> System calls just requires a trap command.

Question 44

Most modern systems use _________

Answer 44

system calls

Question 45

what is a modular os architecture

Answer 45

implements each manager in its own software module Interaction among various managers via abstract data type

Question 46

what is monolithic kernel implementation

Answer 46

Four basic modules are combined into a single software module

Question 47

what is the Microkernel approach

Answer 47

--> Employs a small kernel that implements only the essential and critical functions --> Reminder functions are implemented outside the kernel, possibly in separate modules

Question 48

disadvantage of modular os

Answer 48

Frequent calls incur performance penalty Sacrifice modularity for performance

Question 49

why I/O and memory instructions are privileged instructions.

Answer 49

The OS is solely responsible for managing the memory and IO devices. User programs can only execute non-priveleged instructions. Thus, having I/O and memory instructions privileged ensures that user programs cannot directly manipulate the memory or the devices.

Question 50

Suggest some reasons why UNIX is a monolithic kernel.

Answer 50

In the early days of computing, it is much more efficient to lump the code for the various managers together. Combining the code does not require abstractions between the managers, thus reducing unnecessary code. The various managers’ tasks require a high level of interaction among them. Coupling them into a single code enables that interaction to be done efficiently.

Question 51

what is resource abstraction

Answer 51

hides the actual tasks needed to use the computer resources to use the computer resources by providing simpler commands for user programs

Question 52

What are some of the factors that differentiate between the time to do a normal procedure call from an application program to one of its own procedures, compared to the time it takes to perform a system call to an OS procedure?

Answer 52

--> In normal procedure call, the ‘jump’ from the main program to the procedure is within the user space. The processor need NOT change mode. Thus, it is simpler and takes a shorter time. --> A system call requires the processor to change mode. The processort also has to ‘jump’ from the user program to the relevant trap function. The trap table needs to be consulted to find the correct trap function to execute. All these functions involve more operations, hence is more complex and takes a longer time.

Question 53

windows NT is a ________

Answer 53

microkernel implementation