ITFN 3601 Operating Systems

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ITFN 3601 Operating Systems

• Byron Jeff
• byronjeff_at_clayton.eduComputer Hardware Review
• OS Concepts Overview

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Agenda

• OS Introduction
• Flavors of OS
• Hardware Review
• OS Concepts Overview
• System Calls
• Various OS Approaches

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So What is an OS?

• And Ya Cant Say
• Operating System

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OS Placement
Applications (Word, IE, Games, etc.)?
User
Low-level apps (compilers, interpreters, editors)?
Operating System
Machine Language (Binary)?
Machine
Microarchitecture (processor-level)?
Physical Devices (Hardware)?
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OS Defined

• Abstract Interface
• Service provider for hardware
• Abstracts the details of the machine
• Provides an API (system calls) to user
• Resource Manager
• Multiple users, multiple resources
• Orderly, controlled allocation of resources
• Fairness, protection, space-time, etc.

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History of Operating Systems

• Machine-centric ? Human-centric
• Vacuum Tubes (1945-1955)?
• All programming done in machine language
• No OS,
• Usage done by the same people who built the
  machine

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History of OS (cont)?

• Transistors Batch (1955-1965)?
• University, government, big-business
• Mainframes operators in dedicated rooms
• Punch cards
• Deck readers
• Input/Output bins
• Batch processing onto tape

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History of OS (cont)?

• Integrated Circuits (1965-1980)?
• Software-compatible product lines
• Birth of the modern notion of the OS
• Multi-purpose machine w/ software (OS)
  intermediary
• Multiprogramming (multiple programs/jobs sharing
  resources)?
• UNIX

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History of OS (cont)?

• Personal Computing (1980-present)?
• LSI chips
• Cheap memory, disk space, processing, etc.
• DOS, Windows, Mac OS, X
• Distributed computing
• PDA/embedded-devices

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Flavors of OS

• Mainframe
• Server
• Multiprocessor
• Personal Computer
• Real-Time
• Embedded
• Smart Card

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Mainframe OS

• High-end I/O capacity
• 1000 disks
• Gigabytes of data
• High-end web servers
• B2B (business to business) E-commerce
• High-speed VR/FMV Rendering
• Many small, simultaneous jobs

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Server OS

• Large personal computers (kahuna, zidane, etc.)?
• Print, file servers for small businesses
• Web servers
• Can load balance these to increase performance
• UNIX, Linux, Win2000 Server OS

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Multiprocessor OS

• Connect multiple computers together
• Share/distribute jobs among multiple
  machines/processors
• Specialized protocols for managing communication
• Win2000 Advanced Server

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Personal Computer OS

• Focus on single user, multiple jobs
• What youre running on your machine
• Windows XP/Vista, Win2003/2008 Pro, Linux

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Real-Time OS

• Time dominates these machines specs
• Data collection from production lines, factory
  machinery
• Hard real-time time critical in all instances
• Soft real-time OK to drop occasionally

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Embedded OS

• Personal Digital Assistants
• TVs, microwaves, mobile phones
• Very small OS, embedded on chip
• PalmOS, WinCE

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Smart Card OS

• Credit card sized devices
• Specialized OS for specialized purposes
• E-payment cards (e-cash cards)?
• Some JVM coming into play

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Hardware Review
CPU
Memory
Display
Display Controller
Bus
Keyboard
Keyboard Controller
Floppy
Floppy Controller
Hard Disk
Hard Disk Controller
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Hardware Review

• Processors
• Memory
• I/O Devices
• Bus

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Processors

• Brain of the computer
• Fetch, decode, execute cycle
• Registers
• Program Counter (PC)?
• Stack Pointer (SP)?
• Pipelining improves performance, but complexities
  of rolling back appear
• Kernel vs. User Mode (enables establishing
  limitations of instruction set available)?

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Memory

• Trade off of speed vs. cost/size
• Registers (on processor)?
• Cache (processor)?
• Cache (mainboard)?
• Main Memory
• Disk
• Other Network Cache/Machines
• Tape

Cost increases
Speed decreases
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Memory Allocation

• We need a protective and fair way of allocating
  and resizing memory blocks for processes/jobs
• Two sections of memory
• Code (typically static)?
• Data (volatile)?

Limit
User 2 Data
Base
Limit
User 1 Data
Base
Limit
Program Code
Base
OS
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I/O Devices

• Typically consist of two parts
• Controller
• Device
• Controller manages presents the API of the
  device to the OS
• The software that talks to the controller is
  called a device driver

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Invoking Device Actions

• Busy wait execute a kernel-level system call
  and wait (ties up the processor ?)?
• Ask the device to generate an interrupt (signal
  that its done or failed)?
• Doesnt tie up the processor
• Adds complexity
• DMA Direct Memory Access
• Bypasses the use of the processor
• Allows the device to write directly to memory
  once the rules of the road are established

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Bus

• Communication highway for all data to travel
  upon
• Multiple buses exist in modern machines
• Cache (fastest)?
• Local (on mainboard other busses connect to it)?
• Memory
• PCI (successor of ISA - high-speed I/O)?
• SCSI (high-speed scanners disks)?
• USB (slow peripherals)?
• IDE (disks, etc.)?
• ISA (slowest legacy)?

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OS Concepts

• Processes
• Deadlock
• Memory Management
• I/O
• Files
• Security

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Processes

• Defined as a program in execution
• AKA a job
• Contain
• Instructions (code segment)?
• SP, PC, registers, file handles
• Data segment
• Processes can spawn subprocesses threads
• The OS must ensure fairness protection,
  timeslicing managing multiple processes at a
  time

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Deadlock

• Two or more processes stalemated because they
  cant make progress

Process A Has resource 1 Waiting on resource 2
Process B Has resource 2 Waiting on resource 1
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Memory Management

• Providing protection of one process memory
  section from another process (security)?
• Providing a fair allocation of memory to multiple
  processes
• Swapping memory to disk as needed

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Input/Output

• All OS must manage I/O devices
• Two categories
• Device independent
• Device dependant (device drivers)?

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Files

• System calls
• Create, remove, read, write, etc.
• Directories subdirectories
• Create, remove, rename, move, etc.

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Security

• Allocate permissions
• Directories
• Files
• Example UNIX policies to consider
• Read, Write, Execute
• User, Group, World

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System Calls

• Services that the OS provides to the user
• Set of API that user-level programs may invoke
• Flavors of System Calls
• UNIX
• Win32

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UNIX System Calls

• pid fork() creates child process
• exit() terminates process
• fd open(file, ) opens file
• s mkdir(name, mode) creates directory
• s chmod(name, mode) sets file/dir permissions
• s kill(pid, signal) sends signal to process

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Win32 System Calls

• CreateProcess() creates new process
• ExitProcess() terminates process
• CreateFile() opens file
• CreateDirectory() creates directory

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Approaches to OS

• Monolithic
• Virtual Machines
• Client-Server (microkernel)?

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Monolithic OS Architecture

• OS written as a set of procedures
• Each procedure has well-defined interface
  (parameters)?
• Very little structure or information hiding

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Virtual Machine OS Architecture

• Replicate the hardware within software
• Trap OS calls and translate/handle them
• Breaks down if you make direct I/O calls
• Slow
• Other approach JVM (define an alternate
  instruction set and translate to various OS)?

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Client-Server OS Architecture

• Implement as much as possible in user-level
  modules
• The OS is as small as possible
• It only serves to translate and message pass
  OS-level calls to service processes

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Summary

• Various levels of OS complexities/sizes exist
  (mainframe to smart cards)?
• Important to know your hardware
• Processors, memory, I/O, buses
• Important topics in OS forthcoming
• Processes, deadlock, mem mgmt, files, etc.
• System calls provide an API to user-level
  programs
• Varied OS architecture approaches
• Monolithic, VM, client-server

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FIN