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% MODIFIED by Jonathan Kew, 2008-07-06
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\title[OPS-332: OS] % (optional, use only with long paper titles)
{ Lecture 2 - Fundamental Concepts}

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\author [Bibhas Ghoshal]% (optional, use only with lots of authors)
{ Instructor : Bibhas Ghoshal (\textcolor{black}{bibhas.ghoshal@iiita.ac.in})} 



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 % Department of Computer Science and Engineering\\
 % Indian Institute of Technology, Kharagpur}

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  %Department of Theoretical Philosophy\\
  %University of Elsewhere}
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\date% (optional, should be abbreviation of conference name)
{Autumn Semester, 2015}
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%\subject{Theoretical Computer Science}
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\begin{document}

\begin{frame}
  \titlepage
\end{frame}

\begin{frame}{Lecture Outline}
  \begin{itemize}
   \item Operating System Overview : Re-visit
   \item Computer System Operation - Quick visit
   \item Interacting with services provided by the OS
	  \begin{itemize}
	   \item System calls - link between application programs and OS
	   \item System programs - users interact using programs
	  \end{itemize}
   \item Installation, customization etc.
        \begin{itemize}
         \item booting
        \end{itemize}

  \end{itemize}
        
\textcolor{red}{References and Illustrations have been used from:}
 \begin{itemize}
  \item lecture slides of the book - Operating System Concepts by Silberschatz, Galvin and Gagne, 2005 
  \item Modern Operating System by Andrew S. Tanenbaum
  \item lecture slides of CSE 30341: Operating Systems (Instructor : Surendar Chandra), 
 \end{itemize}

  
\end{frame}


\section{Operating System Overview : Re-visit}
\begin{frame}{Operating system Overview}
\begin{itemize} 
 
\item {Operating System allows the user to achieve the intended purpose of using the computer system in a fast and efficient manner}
 

        
\item {Operating system controls and coordinates use of hardware among various applications and users}

\end{itemize}
\underline{Key concerns of Operating System}
\begin{itemize}
\item Programs
\item Resources
\item Scheduling
\item Protection

%    \item Programs - load a program into memory, run the program, end execution, either normally or abnormally 
%                     (indicating error). A running program requires I/O, which may involve a file, an I/O device, shared with other programs or computers
%          
%     \item Resources - Ensuring availability of resources and allocating them to programs. 
% 
%     \item Scheduling - Deciding when and how long to devote the CPU to a program. Since, main memory is expensive, we use   
%           hierarchy and move stuff around to achieve cost benefits and speed
%    \item Protection - Protect data and programs against interference from other users and their programs
  \end{itemize}
\end{frame}


\begin{frame}{Computer System}
 \begin{figure}
  \centering
  \includegraphics[width=1.0\textwidth]{computer_system.pdf}
  \caption{Computer System}
 \end{figure}

\end{frame}
\begin{frame}{Operating System Overview}
\underline{Operating System Structure}
 \begin{itemize}
  \item Multiprogramming needed for efficiency
  \item Timesharing (multitasking)
  \item Multi-user 
  \item OS should protect the users/processes from each other as well as protect itself from users
  \item Dual-mode operation allows OS to protect itself and other system components
\end{itemize}
 \end{frame}

\begin{frame}{Issues with multi-programming}
\textbf{Problems Associated:}
 \begin{itemize}
  \item How to protect programs from one another and kernel from them all?
  \item How to handle relocation?
 \end{itemize}
\textbf{Solution : } equip CPU with special hardware\\ For example : \emph{Base register} and \emph{Limit register} to handle relocation problem
\end{frame}

\begin{frame}{Solution to re-location problem : Use of base-limit pair}
 \begin{figure}
  \centering
  \includegraphics[width=0.9\textwidth]{relocation_problem_soln.pdf}
  \caption{Use of base-limit pair}
 \end{figure}
\end{frame}


\begin{frame}{Hardware Control Aspect of the Operating System}
\begin{itemize}
  \item Acts as an intermediary between user and hardware
    
  \item Resource allocator
    
  \item Control program
  \newline 
  Operating Systems cannot make hardware \textcolor{red}{go faster}. However, OS can make hardware \textcolor{red}{appear faster}.
   
\end{itemize}
\end{frame}


\begin{frame}{Computer Hardware Review}{Hardware issues of concern to OS Designers}
\textbf{\underline{Computer System}} : CPU, Memory and I/O connected through buses to communicate among each other
 \begin{itemize}
  \item CPU : Fetches instruction from memory and executes them
       \begin{itemize}
        \item CPU has specific instruction set that it executes
        \item Registers  - General Purpose and Special Purpose (\emph{Program Counter} and \emph{Stack Pointer})
        \item \emph{Program Status Word} : contains condition code bits, CPU priority, mode (kernel/user) etc. PSW plays important role in system calls and I/O
        \item Techniques to improve performance : Pipelining, Superscalar CPU etc.
        
       \end{itemize}
  \item Memory : Should be extremely fast, abundantly large and cheap \textcolor{red}{No technology satisfies it :-(}
 \end{itemize}

\end{frame}

\begin{frame}{Storage Structure}
\begin{figure}
  \centering
  \includegraphics[width=1.0\textwidth]{storage_structure.pdf}
  \caption{Storage structure}
 \end{figure}
 
\end{frame}




\begin{frame}{Caching Principle}
\begin{itemize}
 \item Caching is an important principle, performed at many levels in a computer (in hardware, operating system, software)
 \item Information “in use” is copied from slower to faster storage temporarily
 \item Faster storage (cache) checked first to determine if information is there
       \begin{itemize}
	    \item If it is (cache hit), information used directly from the cache (fast)
	    \item If not (cache miss), data copied to cache and used there
	    \item May need to evict some other data (cache replacement)
    
       \end{itemize}
  \item Cache smaller than storage being cached
	\begin{itemize}
	 \item Cache management important design problem
	 \item Cache size and replacement policies are important
	 \item Sometimes bring data before needed (pre-fetch)
	\end{itemize}

  \end{itemize}

 
\end{frame}




\begin{frame}{Memory management and Protection}
\begin{itemize}
 \item \underline{\textbf{Memory Management}:} \\ CPU $>$ memory management unit (MMU) $>$ cache $>$ main memory
 \item \underline{\textbf{Memory Protection}:}\\ memory bound registers - LBR and UBR
\end{itemize}
\end{frame}

\begin{frame}{I/O Subsystem}
\begin{itemize}
 \item Programmed I/O
 \item Interrrupt driven I/O
 \item Direct Memory Access
\end{itemize}

\underline{\textbf{Types of Interrupt: }}
 \begin{itemize}
  
  \item Program Interrupt - conditions requiring supervisor attention
  \item I/O interrrupt - I/O completion or I/O malfunction
  \item Timer interrupt - interval timer of the system
 \end{itemize}

 \underline{\textbf{Steps in Interrupt action: }}
 \begin{itemize}
  
  \item Set interrupt code - interrupt h/w forms a code (stored in PSW) describing cause of interrupt. 
  \item save the PSW - PSW is copied into the saved PSW information area
  \item load interrupt vector
 \end{itemize}


\end{frame}

\begin{frame}{Interrrupt Processing}
 \begin{figure}
  \centering
  \includegraphics[width=0.65\textwidth]{interrupt_driven_op_kernel.pdf}
  %\caption{Interrupt operation}
 \end{figure}
\end{frame}





\section{OS Fundamentals}

\begin{frame}{Some Fundamental Concepts about OS}
\begin{itemize}
 \item Process
 \item Memory 
 \item Files
\end{itemize}

\textbf{Process}  : Program in execution\\
 \begin{itemize}
  \item Address Space - list of address locations which the process can read or write. Address space contains the following:
      \begin{itemize}
       \item program, program's data and stack
       \item registers associated with the program
       \item \emph{Program counter} and \emph{Stack Pointer}
       \item \emph{PSW}
      \end{itemize}
\item When a process is suspended temporarily (such as in time sharing system), it must be restarted in the same state in which it was stopped - information about process needs to be saved
   \begin{itemize}
    \item information of a suspended process is stored in \textbf{process table} 
   \end{itemize}

%\item Key process management system calls are those dealing with creation and termination of processes.
\textcolor{red} {Deadlock} : Two interacting process get into a stalemate position through which they cannot get out (Analogous to deadlock in traffic)
 \end{itemize}

 
\end{frame}



\begin{frame}{Operating System Generation}
\begin{itemize}
 \item Operating systems are designed to run on any of a class of machines; the system must be configured for each specific computer site
 \item SYSGEN program obtains information concerning the specific configuration of the hardware system
 \item Booting – starting a computer by loading the kernel
 \item Bootstrap program – code stored in ROM that is able to locate the kernel, load it into memory, and start its execution
\end{itemize}

 
\end{frame}


\begin{frame}{System Boot}
Operating system must be made available to hardware so hardware can start it
 \begin{itemize}
  \item Small piece of code – bootstrap loader, locates the kernel, loads it into memory, and starts it
  \item Sometimes two-step process where boot block at fixed location loads bootstrap loader
  \item When power initialized on system, execution starts at a fixed memory location - Firmware used to hold initial boot code
 \end{itemize}

\end{frame}








\begin{frame}{Interfacing with OS}
\underline{User Interface}
\begin{itemize}
 \item \textbf{Command Line Interface (CLI)} : The command line may itself perform functions or call other system programs to implement functions (e.g. in UNIX, /bin/rm to remove files). Examples are \textbf{shell} in \emph{UNIX} and \textbf{command.exe} in \emph{Windows} 
     
\item \textbf{Graphics User Interface (GUI)} :  Point and click interface. Examples are \emph{MS windows, MAC OS X Aqua, Unix X} \& variants. 
\item \textbf{Batch} :  Commands are given using a file/command script to the OS and are executed with little user interaction. Examples are  \textbf{.bat} files in \emph{DOS}, \textbf{shell scripts}
\end{itemize}

 
\end{frame}


\section{Interacting with services provided with OS}
\begin{frame}{System Calls}
\begin{itemize}
 \item Programming interface to the services provided by the OS
\item Typically written in a high-level language (\emph{C, C++})
\item Mostly accessed by programs via a high-level \textbf{Application Program Interface (API)} rather than direct system call use
\item Three most common APIs are \textbf{Win32 API} for \emph{Windows}, \textbf{POSIX API} for \emph{POSIX-based systems}
(including virtually all versions of \emph{UNIX, Linux, and Mac OS X}), and \textbf{Java API} for the \emph{Java virtual
machine (JVM)}
\item Why use APIs rather than system calls?
   \begin{itemize}
      \item Underlying systems calls (error codes) can be more complicated. API gives a uniform, portable interface
   \end{itemize}
\end{itemize}

 
\end{frame}








\begin{frame}{Example of System call}
\begin{itemize}
 \item System call sequence to copy the contents of one file to another file (POSIX like C pseudo code) (bold are API system calls)
\end{itemize}

 \textbf{write}(1, “Input file”, 11);\\
 \textbf{read}(0, \&buffer, 100);\\
 ...........\\
 fd = \textbf{open}(buffer,O\_RDONLY);\\
 outfd = \textbf{open}(buffer,O\_WRONLY$|$O\_CREAT$|$O\_TRUNC,0666);\\
 if(outfd$<$0)\textbf{abort}(``File creation failed'');\\
 ............\\
 \textbf{closefd};\\
\end{frame}

\begin{frame}{Standard C library example}
C program invoking \textbf{printf} library call which calls \textbf{write} system call
 \begin{figure}
  \centering
  \includegraphics[width=0.9\textwidth]{system_call_ex.pdf}
  \caption{Example of system call}
 \end{figure}
\end{frame}

\begin{frame}{System Call Implementation}
 \begin{itemize}
  \item A number associated with each system call
      \begin{itemize}
      \item System-call interface maintains a table indexed according to these numbers\\
            Additional info: check /usr/include/sys/syscall.h
     \end{itemize}

  \item The system call interface invokes intended system call in OS kernel and returns status of the system call and any return values

  \item The caller need know nothing about how the system call is implemented
  \begin{itemize}
      \item Just needs to obey API and understand what OS will do as a result call
\item Details of OS interface hidden from programmer by API
\item Managed by run-time support library (set of functions built into libraries included with compiler)
     \end{itemize}
 \end{itemize}

 
 
\end{frame}


\begin{frame}{API – System Call – OS Relationship}
 \begin{figure}
  \centering
  \includegraphics[width=0.65\textwidth]{api_system_call.pdf}
  \caption{api system call}
 \end{figure}
\end{frame}


\begin{frame}{System Call Parameter Passing} 
 \begin{itemize}
  \item More information is required than simply identity of desired system call
  \item Three general methods used to pass parameters to the OS
     \begin{itemize}
      \item Simplest:  pass the parameters in hardware registers
 
       \item Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register 
             (This approach taken by Linux and Solaris)
        \item Parameters placed, or pushed, onto the stack by the program and popped off the stack by the operating system.
              Block and stack methods do not limit the number or length of parameters being passed
     \end{itemize}

 \end{itemize}

\end{frame}


\begin{frame}{Parameter Passing via Table}
 \begin{figure}
  \centering
  \includegraphics[width=0.9\textwidth]{parameter_passing.pdf}
  \caption{}
 \end{figure}
\end{frame}


\begin{frame}{System programs}
\begin{itemize}
 \item Provide a convenient environment for program development and execution. Some of them are simply user interfaces to system calls; others are considerably more complex
   \begin{itemize}
    \item File management - Create, delete, copy, edit, rename, print, dump, list, and generally manipulate files and directories
    \item Programming-language support - Compilers, assemblers, debuggers and interpreters sometimes provided
    \item Program loading and execution- Absolute loaders, relocatable loaders, linkage editors, and overlay-loaders, debugging systems for higher-level and machine language
    \item Communications - chat, web browsing, email, remote login, file transfers
    \item Status information - system info such as date, time, amount of available memory, disk space, number of users
   \end{itemize}

\end{itemize}

 
\end{frame}


\begin{frame}
 
\end{frame}






\end{document}