Operating Systems

Operating Systems

A program that manages hardware and provides other programs with an environment to run in

Process

program in execution

OS Kernel

Central component of O.S that performs the most important OS tasks

system call

request for service from an application to the operating system

multitasking

technique to fake simuntaneous processes on a single CPU core

virtual memory

technique to fake larger RAM memoy with hard disk

Interrupt

a signal about important event that requires immediate attention

Drivers

small program that handles communication between operating system and devices

files

related data stored in hardisk on one name

file system

collection of data about all files on the computer, including physical coordinates of files on hardisk

operating system api

set of tools the O.S providers for programmers to use, making it convienent, Extra level of abstraction

Logical Disk Partition

portion of hardisk described in a seperate file system

Networking Adaptor

A piece of hardware that recieves and sends data physically through the network

Protocol

bunch of rules on how to send/recieve and understand data

Process Control Block (PCB)

record for a single process maintained by the operating system

PID

Process Identification Number, all unique

context switch

sequence of steps that CPU goes through to switch execution from one process to another

Heap

process that does dynamic memory allocation

Stack

All data belonging to function

Process States

New State: process created, not ready to do anything
Ready Queue: collection of processes ready and willing to use CPU
Running: Process is using CPU
Waiting: I/O queue, collection of processes to use corresponding I/O device, does not wait to use CPU
Terminated: PCB remains, process terminated

POSIX

set of standards that define how Unix-like operating systems should behave to maintain compatibility across systems.

FORK

command allows us to utilize more than one core on computer

EXEC(“executable_name”)

erases all process content and loads instruction and data from executable file mentioned in parameter

exit(0)

Way to exit, the number inside is a status code

wait()

pause the process until it’s child terminates

zombie process

process that call exit but whos parent hasn’t called wait yet

orphan process

process when parent has exited

IPC (Inter-Process Communication)

Tools for allowing programs to talk to each other:

Message Passing, Shared Memory

Message Passing

OS sends the message each time to ask the O.S you need a system call
- slower

+ easier to program correctly

+ can be used by processes on different computers (networking)

Shared Memory

O.S establishes shared memory (shared RAM) between different processes and can read/write and vice versa. Only need one system call

Web Server

program that manages web pages, manages request from browsers

DNS server

gets URL and returns corresponding IP address

Networking Ports

unique numeric identifiers given to any process that wants to use the network

Well known networking ports

networking ports reserved for specific purpose, predetermined purpose

networking socket

combo of IP addresses and networking ports

Thread (thread of execution)

independent execution of program code from a seperate program counter

Ready Queue

collection of processes ready and willing to use CPU

What do threads share?

• Text section (program code)

• Data section (global & static variables)

• Heap (dynamically allocated memory, e.g. malloc, new)

What don’t threads share?

• Stack

• Stack pointer / registers

• Local variables (function calls, etc.)

Thread vs Processes

Threads are:

• Fast to create and delete

• Memory efficient (copy nothing, created inside process)

• Context switching is faster

• Shared memory by default

Processes are:

• Can run exec()

• Fault-independent

Fault independence

One process doing something bad doesn’t mean other processes are bad

Kernel Thread

threads managed with O.S helps, the O.S knows about that and can manage them seperatly and efficiently.

User Threads

Threads managed without the help of O.S → fast to manage, cannot use multiple cores, one thread books all (faster than kernel threads)

Hardware Threads

Amount of threads your CPU run simultaneously

Thread Local storage

A tool that allows you to create a variable that is global but still private for each thread

Thread pool

Maximum number of threads created then put to sleep, when a user request arrives you wake up one of the created threads, once finished using you freeze it and return it to thread pool.

Context Switch

 A sequence of steps to change CPU from running one process to running another process.

• Pause process 1

• Save all general purpose CPU register and PC of P1 (saving context)

• Load all general purpose CPU register and PC of P2 (loading next)

• Resume Process 2 (Slow because it accesses information from RAM memory)