Operating Systems test 1 (ch1-2.6)

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operating system (OS)

the software that runs on the bare hardware of a computer and provides essential support for users to develop and use applications in the most efficient and safe manner

CPU

Machine instructions perform \n operations on contents of \n registers and memory locations

Main \n memory

Physical memory is a linear \n sequence of addressable bytes \n or words that hold programs \n and data

Secondary storage

Disk and other secondary \n storage devices are multi- \n dimensional structures,

The hardware/user gap is bridged by the OS or by other system software. Does this require OS support: Input a character from the keyboard?

Definitely

The hardware/user gap is bridged by the OS or by other system software. Does this require OS support: Invoking a high level matrix manipulation

Not Necessarily

The hardware/user gap is bridged by the OS or by other system software. Does this require OS support: Allocate n bytes of memory for a new data structure

Most likely

The hardware/user gap is bridged by the OS or by other system software. Does this require OS support: Load a program into memory

Definitely

The hardware/user gap is bridged by the OS or by other system software. Does this require OS support: Change the layout of a document

Not Necessarily

The hardware/user gap is bridged by the OS or by other system software. Does this require OS support: Call a shared library function

Most likely

The hardware/user gap is bridged by the OS or by other system software. Does this require OS support: Call a function defined in the current pogram

Not Necessarily

The hardware/user gap is bridged by the OS or by other system software. Does this require OS support: Exit current program

Definitely

Abstraction

the act of removing unimportant details or attributes of objects in order to construct more general and less complex objects

Virtualization

is the act of creating the illusion of having one or more objects with more desirable characteristics than the real object.

### The OS as a resource manager

One of the main tasks of an OS is to optimize the use of all computational resources to ensure good overall performance, while satisfying the requirements of specific applications, including guaranteeing acceptable response times for interactive processes, meeting deadlines of time-critical tasks, and allowing safe communication among different tasks.

***Multiprogramming*** 

 a technique that keeps several programs active in memory and switches execution among the different programs to maximize the use of the CPU and other resources

***Time-sharing*** (***multitasking)***

is an extension of multiprogramming where the CPU is switched periodically among all active computations to guarantee acceptable response times to each user.

Multiprogramming generally improves CPU utilization and throughput.

True

The main objective of time-sharing is to improve resource utilization.

False

Multiprogramming and time-sharing are not used together.

False

To achieve best CPU utilization, _____ computations should run simultaneously.

More than 2

The use of time-sharing will 

Guarantee reasonable response to each computation

Processes p1 and p2 share a single CPU and 2 independent I/O devices. Each process executes a compute-bound phase of 10 time units followed by an I/O-bound phase of 10 units. W/O multiprg

40

Processes p1 and p2 share a single CPU and 2 independent I/O devices. Each process executes a compute-bound phase of 10 time units followed by an I/O-bound phase of 10 units. WITH multiprg

30

Abstraction can be used without virtualization.

Yes, abstraction can be used without virtualization. Abstraction creates objects that are more general and less complex. Those objects do not necessarily need to be virtual objects.

Virtualization can be used without abstraction.

Virtualization can be used without abstraction. Yes, virtualization can be used without abstraction. Virtualization creates the illusion of a new object.

Abstraction and virtualization can be used together.

Yes, abstraction and virtualization can be used together. Virtualization can be used to create the illusion of a new object. Abstraction can then be used to further improve the new object by making it more general and easier to use.

What do multiprogramming and time-sharing have in common? What are differences between the two concepts?

Multiprogramming allows multiple programs to be active in memory simultaneously. While \n one is waiting for I/O completion or some other event, another can run on the CPU. The main objective is to increase CPU and device utilization

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Time sharing goes beyond multiprogramming by guaranteeing that each computation gets a

\n turn at the CPU in a timely manner, not only when other computations block to wait for a \n resource

kernel

 the minimal set of functions necessary to manage the system resources safely and efficiently. 

privileged instruction

performs critical operations that access I/O devices and the CPU's status and control registers. Thus only the OS kernel is allowed to execute privileged instructions.

Kernel Mode

  the CPU state where both privileged and non-privileged instructions may be used.

User mode

the CPU state where only non-privileged instructions may be used. Any attempt to execute a privileged instruction in user mode automatically transfers control to the kernel.

The OS kernel is the lowest level of software and provides the basic functionalities necessary for efficiently and safely executing programs

True

The kernel is extended by library functions, which invoke kernel functions to offer more convenient service functions to higher-level software.

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True

Applications and system software may invoke kernel functions directly or use the more convenient higher-level abstractions provided by library functions.

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True

Kernel functions may be invoked by

any program

Privileged instructions may be executed by

only the kernel

An application that needs to access an I/O device could not be written without

Kernel functions

The kernel can execute _____ instructions

Both non privileged and privileged

***graphical user interface*** (***GUI)***

 presets various icons on the screen, which the user can click on in different ways to invoke services associated with the icons, or to reveal pull-down menus for additional tasks.

OS shell 

 a command interpreter that accepts and interprets textual commands issued by the user via a keyboard.

shell script

a program that implements a new operation by combining multiple commands and control statement into one named unit interpreted by the shell.

A script can use an iteration variable, i. The value $i of i can be used to create a different name in each iteration. The script below creates 10 directories named D0, D1, ..., D9, where MKDIR is the command to make a directory.

To create the same directories using a GUI, the user must perform some number of right and left-clicks, type some number of characters, and press Enter several times.

10

A script can use an iteration variable, i. The value $i of i can be used to create a different name in each iteration. The script below creates 10 directories named D0, D1, ..., D9, where MKDIR is the command to make a directory.

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The required number of right-clicks is

10

A script can use an iteration variable, i. The value $i of i can be used to create a different name in each iteration. The script below creates 10 directories named D0, D1, ..., D9, where MKDIR is the command to make a directory.

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The number of characters typed is

20

A script can use an iteration variable, i. The value $i of i can be used to create a different name in each iteration. The script below creates 10 directories named D0, D1, ..., D9, where MKDIR is the command to make a directory.

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The number of times Enter is pressed is

10

 ***system call*** 

a request from an application for an OS service. A system call is implemented as a library function, which sets up the necessary parameters for the requested operation and issues a corresponding supervisor call.

 ***supervisor call*** (***kernel call***)

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

A supervisor call is similar to a function call with two special features:


1. The call switches execution from user mode to kernel mode by setting the mode bit in the CPU.
2. To prevent a call from branching to arbitrary locations within the kernel, the function to be invoked is not specified by an address but indirectly using an index into a branch vector. Thus kernel-mode execution is limited to only well-defined entry points within the kernel.

True

A system call is a

Library function

A supervisor call is a

Privileged instruction

A supervisor call can be executed 

by any program

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

from user mode to kernel mode

interrupt

an event that diverts the current execution of a program to a predefined location in the kernel in order to respond to an event. An interrupt is triggered by a hardware signal sent to the CPU from an external device.

trap

an interrupt triggered by the currently executing instruction. Dividing by zero, executing an invalid opcode, or causing an arithmetic overflow are all errors, which result in a trap and cause the OS to abort the current program execution.

***interrupt handler*** 

a kernel function, invoked whenever an interrupt occurs, that determines the cause of the interrupt and invokes the appropriate kernel function to provide the response

An application is requesting a service from the OS, which consists of several steps. The current step is: Setup parameters for the service in user mode. What is the next step?

Execute supervisor_call in user mode.

An application is requesting an I/O operation from the OS, which consists of several steps. The current step is: Setup parameters for the service in user mode. What are the next two steps?

Execute supervisor_call in user mode.

Execute kernel function in kernel mode.

What do interrupts and traps have in common?

Traps and interrupts both suspend the execution of the current instruction sequence and temporarily divert control to a dedicated area within the OS kernel

What are the differences between the two concepts?

An interrupt is caused by an event external to the current execution. Ex: The completion of an I/O operation or a time-out signal from a clock. Interrupts are asynchronous to the current execution in that the interruption may occur unpredictably between any two instructions.

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A trap is a special case of an interrupt caused by an event internal to the current execution. \n Ex: The execution of a privileged instruction or an arithmetic overow. \n Traps are synchronous to the current execution, in that the interruption is caused by the \n currently executing instruction. The interruption can be unintentional, as in the case of an \n error, or intentional, as in the case of a supervisor call.

Is multiprogramming possible without interrupts

Multiprogramming does not require interrupts. A context switch happens whenever a computation terminates or blocks to wait for I/O.

Is time-sharing possible without interrupts?

\n Time sharing requires a periodic interrupt to prevent long-running computations from monopolizing the CPU and thus delaying other computations for unpredictable amounts of \n time

Enabling hardware technology: vacuum tubes

OS type: none

Enabling hardware technology: Transistors replaced \n vacuum tubes as smaller and faster switches

OS type: Batch os

Enabling hardware technology: Integrated circuits allowed the development of microchips to replace \n individual transistors

OS type: Interactive multi user OS

Enabling hardware technology: Very large-scale integration (VLSI) allowed the placement of a \n complete microprocessor on a single chip, leading to \n the development ofpersonal computers(PCs)

OS Type: Desktop and Laptop OS

Enabling hardware technology: Networking hardware \n enabled the harnessing of the power of multiple computers

OS Type: for supercomputers, distributed systems, and \n mobile devices

The invention of transistors marks the transition to the _____ generation of computer systems.

2nd

The invention of integrated circuits marks the transition to the _____ generation of computer systems.

3rd

The invention of microprocessors marks the transition to the _____ generation of computer systems.

4th

Mainframes are considered 

General purpose computers

An advanced aircraft is likely to have a _____ on board to help control the aircraft

real time computer

What multiprocessors and multi-computers (distributed systems) have in common is

The ability to carry out operations in parallel

***process*** 

an instance of a program being executed by an OS. Ex: When a user opens a new application like a web browser or text editor, the OS creates a new process.

***process control block*** (***PCB***)

A data structure that holds information for a process, including the current instruction address, the execution stack, the set of resources used by the process, and the program being executed. 

An OS uses a PCB to represent a process

True

The PCB is created by the process when execution starts

False

The PCB becomes part of the program being executed by a process.

False

Two processes can be executing the same program.

True

The transition (ready -> running) of a process p is caused by

the OS

The transition (running -> blocked) of a process p is caused by

The process P itself

The transition (running -> ready) of a process p is caused by 

The OS

The transition (blocked -> ready) of a process p is caused by

some other process

A newly created process is placed into

new state

A process is placed into the ***terminated state***

when execution can no longer continue but before the PCB is deleted. Ex: The OS may want to examine the final state of a process that committed a fatal error.

A process may be placed into the ***suspended state***

even though the CPU and all resources are available. Ex: The OS may want to stop a process to allow debugging or to regulate performance.

When a newly created process p is ready to compete for the CPU, p moves itself from the new to the ready state.

False

When a ready process p wishes to temporarily stop competing for the CPU, p moves itself to the suspended state.

When a ready process p wishes to temporarily stop competing for the CPU, p moves itself to the suspended state.

The transition of a process p from running to terminated can be caused by p itself.

True

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When a blocked process p is suspended and the resource needed by p becomes available, p is moved to the ready state.

False

When a process p is moved from the current state (running, ready, or blocked) to the suspended state, then upon reactivation

p is either moved to the read or the blocked state

***context switch*** 

 the transfer of control from one process to another and may be triggered by the OS for scheduling reasons or caused by the inability of the current process to continue.

CPU state

consists of all intermediate values held in any CPU registers and hardware flags at the time of the interruption.

A context switch for a currently running process p may be caused by process p itself

True

A context switch for a currently running process p may be caused by the OS

True

A context switch for a currently running process p may be caused by some other process q

False

The PCB contains an up-to-date copy of the CPU state of a process p _____ .

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when p's state is ready or blocked

Is this valid or invalid? : new ➛ ready ➛ suspended ➛ blocked ➛ suspended.

Invalid

Is this valid? : suspended ➛ blocked ➛ suspended ➛ blocked ➛ ready ➛ running.

Valid

Is this valid? : running ➛ blocked ➛ ready ➛ blocked ➛ suspended.

invalid