Operative Systems

Operative Systems

1. Introduction

   • A program that interacts between an user and a machine
   • Computer System Structure
     • Hardware
     • Operative system
       • A resource allocator
       • A control program
     • Applications
     • Users

2. Operating System Structures

   • Services
     • User Interface (CLI, GUI, Batch)
     • Program execution
     • I/O Operations
     • File-system manipulation
     • Communications
     • Error detection
   • System calls
     • Programming interface to the OS services
     • Mostly acessed by APIs

3. Processes

   • A program in execution
     • Program counter
     • Stack
     • Data section
   • Process states
     • new
     • ready
     • running
     • waiting
     • terminated
   • Process Control Block
     • Information associated with each process

4. Threads

   • The basic unit of processing
   • Thread types
     • User threads (applications)
     • System threads (OS)
   • Multithreading models
     • Many-to-one
     • One-to-one
     • Many-to-many

5. Scheduling

   • Maximizes CPU usage by multiprogramming
   • Scheduling criteria
     • CPU usage
     • Throughput
     • Turnaround time
     • Waiting time
     • Response time
   • Scheduling algorithms
     • First Come First Served
     • Round Robin
     • Shortest Job Come First
     • Shortest Remaining Time First
     • Multilevel Queue
     • Priority scheduling
     • Threads

6. Synchronization

   • Problems
     • Race condition
     • Starvation
     • Inanition
   • Solutions
     • Semaphores
     • Monitors
     • Messages
     • Hardware
       • Test and Set
       • Compare and swap
   • Peterson's Algorithm

7. Deadlocks

   • Characteristics
     • Mutual exclusion
     • No preemption
     • Circular Waiting
     • Hold and Wait
   • How to prevent a Deadlock
     • Prevent it
     • Make it occur and fix it!
     • Ostrich

8. Memory

   • A program must be brought form disk to memory
   • Addessing
     • Physic
     • Logic
   • Fragmentation
     • Extern: Total space disponible for a request, but not contiguous
     • Intern: Allocated memory must be larger than requested
   • Paging
     • Divides physic memory into frames
     • Divides virtual memory into pages
   • Segmentation
     • Memory-management scheme that supports user view of memory

9. File-system

   • Contiguous logical address space
   • Operations
     • Create
     • Read
     • Write
     • Delete
     • Truncate