Operating Systems Flashcards

Operating systems

Check the program format, executable or not? Identify the instruction
and data offset from program header for addressing, create a new process, and link the program. This process will actually
handle the execution of program

An OS ARCHITECTURE serves 3 types of users by

Give users a desktop environment, Give applications a more usable abstraction of the hardware, Give hardware manufacturers an abstraction of the applications

What is the hardware interface

The physical reality

What is the application Interface

The nicer abstraction

System-call interface maintains

a table indexed according to these numbers

Process is

a running instance of a program

CPU Scheduling Information contains

priorities, scheduling and queue pointers

Memory Management Information contains

memory allocated to the process

Accounting Information contains

The CPU used, clock time elapsed
since start, time limits

I/O status information contains

I/O devices allocated to process, list of open files

fork() system call creates

new process

Cascading termination means

all child, grandchild etc., are terminated by OS is parent exits

Processes can communicate only if

they share a mailbox

Non-Blocking is considered

asynchronous

Named Pipes can be accessed without a

parent-child relationship

Stub

client-side proxy for the actual procedure on the server

The client-side stub locates

the server and marshalls the parameters

The User Experience Layer

Defines the software interface that allows users to interact with the computing devices

Application frameworks layer

This layer includes the Cocoa and Cocoa Touch frameworks, which provide an API for the Objective-C and Swift programming languages

Core frameworks

This layer defines frameworks that support graphics and media including, Quicktime and OpenGL

Kernel environment

This environment, also known as Darwin, includes the Mach microkernel and the BSD UNIX kernel. We will elaborate on Darwin shortly.

What do system calls provide

An interface to the services made available by an operating system. These calls are generally available as functions written in C and C++, although certain low-level tasks may have to be written using assembly-language instructions.

A thread is

a basic unit of CPU utilization

Process creation is ________ weight

heavy

Thread creation is _______ weight

light

Concurrency

A multi-threaded application running on a traditional single-core chip would have to interleave the threads

Parallelism

On a multi-core chip, the threads could be spread across the available cores, allowing true parallel processing

OpenMP is a

set of compiler directives available for C, C++, or FORTRAN programs

OpenMP’s main function is to

Instruct the compiler to automatically generate parallel code where appropriate

Concurrent

Removed in FIFO order but several may beat the same time

CPU scheduling decisions may take place when a process

• Switches from running to waiting state, i.e., I/O request or event wait
  - Switches from running to ready state,
  - Switches from waiting to ready, i.e. I/O or events completed
  - Terminates

CPU Utilization

# of work cycle / # of (work + idle) cycle

Throughput

# of processes completed per unit time

Turnaround time

amount of time required for a particular process to complete, from submission time to completion (Wall-clock time)

Waiting time

amount of time a process has been waiting in the ready queue

Response time

The time taken in an interactive program from the issuance of a command to the commence of a response to that command

Race Condition occurs when

two or more threads have access to shared data and they try to change the data at the same time, resulting in dirty data (i.e., data inconsistency) issue

Synchronization uses

synchronized operations to ensure cooperation among multiple threads

Critical Section is a

piece of code to access/update the

shared data; only one thread can

access/update it at a time

Mutual Exclusion

ensures one thread can do something without the interference of other threads

The two parts of Mutual Exclusion are

Liveness and Safety

Liveness Violation

A thread requested access to the critical section, but failed to get it

Primitive atomic operations run

Entirely independently and uninterruptible

Locking Primitives

Reliable atomic synchronization operations

Liveness locks allow

only a single thread into critical section

Mutex stands for

Mutual Exclusion

Semaphore is like a

blocking integer

With each semaphore there is an associated

waiting queue

Monitors

A high-level abstraction that ensures a more reliable, convenient, and effective synchronization mechanism

Readers only

read the data set, they don’t perform any updates

Writers can both

read and write

The first readers-writers problem

gives priority to readers

The second readers-writers problem

gives priority to the writers

The conditions for Deadlocks are

A. Mutual Exclusion: only one thread at

a time can use a resource
B. Hold and Wait: a thread holding at

least one resource is waiting to acquire

additional resources held by other

threads
C. No Preemption
D. Circular Wait

Deadlock prevention ensures that

at least one of the necessary

conditions to cause a deadlock will

never occur

Deadlock avoidance ensures that

the system will not enter an unsafe

state