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| If you're not sure if something is appropriate to be added to the wiki, or you have a question about the bonus marks, ask Reza. | | If you're not sure if something is appropriate to be added to the wiki, or you have a question about the bonus marks, ask Reza. |
| == Course Notes ==
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| === Lecture-1 ===
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| ====Introduction====
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| '''why is an operating system important?'''
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| *Only certain programs run on certain operating systems
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| *Customization
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| *Interface
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| We program at different levels of abstraction
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| *Abstraction - make system easy to use, divide program into smaller understandable
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| pieces
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| *most portable - the web
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| **works on almost all operating systems
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| *the web browser is an operating system (eg: chromebook)
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| '''How do programs run at the same time?'''
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| *Originally, one program used to control the whole system, now for example there are
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| around 270 threads running at once on a laptop
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| *A program executes instructions → '''the processor fetches an instruction from
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| memory, decodes it and executes it'''
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| *Similar to a political system: Authoritarian dictatorship
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| *Virtualizing the CPU: illusion that a single CPU has a large number of smaller virtual
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| CPUs.
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| *Policy: to determine which program runs first
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| '''Operating systems'''
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| *body of software to determine which programs to run, allow programs to share memory,
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| enabling programs to interact with devices
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| *the OS takes a physical resource (such as the processor, or memory, or a disk) and
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| transforms it into a more general, powerful, and easy-to-use virtual form of itself
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| *AKA virtual machine
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| *provides some interfaces (APIs) that you can call (system calls that are available to
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| applications to run programs, access memory and devices, and other related actions,
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| aka standard library)
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| *Resource manager - give programs resources based on priorities
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| '''Goals:'''
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| **High performance
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| **Minimize overhead
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| **protection between applications
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| **Isolating processes
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| **Reliability(runs nonstop)
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| **Energy efficient
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| **Secure
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| **Mobility
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| Unix
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| *Has variants - linux, minux
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| *Programmed in C
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| Windows
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| *VMS
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| *Microsoft bought a team to build an operating system
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| ====Hello World - Sample Program====
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| C programs start with '''main function'''
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| [[File:Lec1-1.png|none|800px]]
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|
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| Compile and Run:
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| [[File:Lec1-2.png|none|800px]]
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| Two different ways to compile:
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| *One does more work and it is smaller
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| *One does less work and it is larger
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| [[File:lec1-3.png|none|800px]]
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|
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| '''How many lines of code are running in a system?'''
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| * 100 million lines of code!
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| '''Questions to ask:'''
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| #Who calls main?
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| #Where do the arguments come from?
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| #Who's taking the return value?
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| #Who defines headers? Where do they come from?
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|
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| '''Mental Model'''
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| *Don’t need to know exactly what happens
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| *Know the strategy to figure it out
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| *Know when to ask the questions
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| *Know when it matters
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| *OS → the code that runs under the application
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| '''Who is in charge?'''
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| *the '''first program''' that runs on the system is in charge
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| **may delegate its powers to others
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| *make sure it only obeys your commands (self preservation)
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| **eg: if you get a command from someone else, ask me first
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| **add a level of abstraction: authorization
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| **downside: labour intensive (time consuming to approve every command)
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| *create rules to determine when authorization is needed
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| **when does the OS need to get involved
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| **this is costly, so leave instructions behind so that is can make decisions
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| **'''take charge of dangerous operations'''
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| '''Cpu modes:'''
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| *'''Supervisor mode''': access to all hardware resources
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| *'''User mode''': access to limited resources, as defined by code running in supervisor mode
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| '''Definitions:'''
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| *Kernel: code that runs in supervisor mode (If your code runs in supervisor mode, you are
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| in the kernel.)
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| *Process: “running program” (Processes run in user mode)
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| *System call: process making a request of the kernel (costly)
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| *portable: able to work on different operating systems, a program that can run in many
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| different environments.
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| '''APIs'''
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| *an application programming interface (API) is a set of subroutine definitions,
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| communication protocols, and tools for building software
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|
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| '''Memory'''
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| *read - address to access data stored there
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| *write - address and data to be stored there
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| *virtualizing memory - each process accesses its own private virtual address space
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| **The OS maps this memory to the physical memory on the machine
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| '''Concurrency'''
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| *working on many things at once in the same program
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| *multi-threaded programs
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| **thread: a function running within the same memory space as other functions
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| *race conditions
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| '''Presistence'''
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| *how do we not lose data
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| *volatile - when the system crashes, the data in this memory is lost (DRAM)
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| *hard drive - long term store
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| *solid state drive - alternative for hard drive
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| *file system - manages disk storage
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| *handling system crashes
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| **journaling or copy-on-write
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| <center>'''END OF LECTURE 1'''</center>
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| ----
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|
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| === Lecture-2===
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| <center>'''Comming Soon!'''</center>
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