Operating System's Layer

Operating System's Layer

1. Operating System

   • It's the system's software that manages computer resources and provides an interfase for system interaction. OS (Operating System) can be divided in two:
     • Application software: programs that help us solve real-world problems.
     • System software: programs that manage a computer system and interact with hardware.
     • Principal OS Factors
       • MEMORY MANAGEMENT: keeping track of how and where programs are loaded in main memory. Memory management follows 3 principles:
         • Single Continous MM: a program is loaded into one continous area of memory
           • Partition MM
             • Paged MM: processes are divided into fixed size pages and stored in memory frames when loaded
       • PROCESS MANAGEMENT: keeping track of information for active processes
         • Process States: the conceptual stages through which a process moves as it is managed by the OS
           • Process Control Block: the data structure used by the OS to manage information about a process
       • CPU SCHEDULING: determining which process in memory is given access to the CPU so that it may execute
         • Nonpreemptive scheduling: CPU scheduling that occurs when the currently executing process gives up the CPU voluntarily
           • Preemptive scheduling: CPU scheduling that occurs when the operating system decides to favor another process, preempting the currently executing process

2. File Systems

   • Directory: a named group of fies
     • Path: a text designation of the location of a file or subdirectory in a file system. Path's can be:
       • Absolute: it begins at the root and includes al succesive sudirectories
       • Relative: it begins at the current working directory
     • Directory tree: a structure showing the rested directory organization of file system
       • Root Directory: the topmost in which all others are contained
         • Working directory: the curretly active subdirectory
   • The file system is the OS'S logical view of the files it manages. A file is a named collection of data
     • File types: specific kind of info contained in a file
       • Text file: a file that contains characters
         • Binary file: a file that contains data in a specific format and requires special interpretation of its bits
     • File Access
       • Sequential: data in a file is accessed in a linear fashion
         • Direct: data in a file is accessed directly by specifying logical record numbers