Operating System Overview

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Operating System Overview

• CS-550 Comparative Operating Systems

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Operating System

• A program that controls the execution of
  application programs
• An interface between applications and hardware

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Operating System Objectives

• Convenience
• Makes the computer more convenient to use
• Efficiency
• Allows computer system resources to be used in an
  efficient manner
• Ability to evolve
• Permit effective development, testing, and
  introduction of new system functions without
  interfering with service

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Layers of Computer System
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Services Provided by the Operating System

• Program development
• Editors and debuggers
• Program execution
• Access to I/O devices
• Controlled access to files
• System access
• Error detection and response
• Accounting

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Operating System as Resource Manager

• Responsible for managing all computer resources
• Functions same way as ordinary computer software
• It is program that is executed
• Operating system relinquishes control of the
  processor to execute other programs

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Kernel

• Portion of operating system that is in main
  memory
• Contains most-frequently used functions
• Also called the nucleus

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Operating Systems History

• Early 1950s
• Systems Univac I, II IBM 701, 704 large, very
  expensive
• Serial Processing
• No operating system
• Machines run from a console with display lights
  and toggle switches, input device, and printer
• Common concerns
• Idle time between jobs
• Setup running a job included loading the
  compiler, source program, saving compiled
  program, and loading and linking
• Every programmer writes routines to control I/O
  devices

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First Generation Simple Batch Systems

• Eastern Joint Computer Conference in 1953
  informal discussion of IBM users
• GM develops input/output system for IBM 701
• Common set of procedures for access to I/O
  devices
• Monitor concept Resides in main memory and
  controls the running programs Batches jobs
  together Program branches back to monitor when
  finished Monitor starts next job
• GM and North American Aviation jointly develop
  supervisor program for IBM 704
• Share Operating System (SOS) developed by IBM
  on 709 for Share user group
• Supervisory control, buffered I/O, symbolic
  assembly language

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First Generation Simple Batch Systems (Cont.)

• Fortran Monitor System (FMS) on IBM 709
• Based on GM/NAA OS, first OS to support
  high-level language programming
• Real-Time and Transaction processing Systems
• SAGE real-time control system (IBM AN/FSQ7
  military system)
• SABRE airline reservation system (IBM for
  American Airlines)
• Tape Operating Systems
• Card input and output temporarily stored on tape
• Commonly used procedures (compilers) kept on tape
• Examples TOS/360 for first S/360, TOS for RCA
  Spectra 70

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First Generation Simple Batch Systems (Cont.)

• Disk Operating Systems
• Direct access to large amounts of data
• Operating systems provided by computer
  manufacturer
• Components resident loader, Job Control Language
  (JCL), Input/Output Control System (IOCS)
• Examples Admiral for Honeywell 1800, EXEC I for
  Univac 1107, Scope for Control Data 6000, Master
  Control Program for Burroughs 5000, IBSYS for IBM
  709 and 7090
• ATLAS
• Developed by Manchester Univ. and Ferranti
• First use of interrupts, extracode (precursor of
  system call instruction), and one-level store
  (precursor of virtual memory)

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First Generation Batch Multiprogramming

• Batch processing each job submitted as a batch
  of cards
• Batch serial jobs processed one at a time, each
  one finishing before new one accepted
• Batch multiprogramming several programs execute
  in interleaved manner and share CPU, memory, I./O
  devices when a program waits for I/O
  completion, CPU given to other program
• SPOOLing (Simultaneous Peripheral Operation
  On-Line)
• Spooler program reads jobs from cards and tapes
  onto disk and copies output from disk to printer

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First Generation Batch Multiprogramming

• Master Control Program (MCP) for Burroughs 5000
  pioneered multiprogramming
• Virtual memory
• Priorities
• High-level languages (Algol, Cobol) supported
  using compilers
• IBM System/360 family (1964)
• Evolvable same program runs on entire family
• DOS/360 interim disk OS
• PCP early version of OS/360
• OS/MFT batch multiprogramming for small S/360s
• OS/MVT batch multiprogramming for large S/360s
• JCL Large and powerful Job Control Language

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Time-Sharing Systems

• Disadvantages of batch systems
• No direct user-program interaction
• Long turnaround time
• Interactive computing
• User and system programs on disk
• JCL commands entered by user directly on terminal
• Time-sharing systems
• Multiple users simultaneously access the system
  through terminals
• Processors time is shared among the multiple
  users
• Time slice (time quantum) limits the amount of
  time (CPU) received by each job

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Time-Sharing Systems (Cont.)

• Compatible Time-Sharing System (CTSS) developed
  in early 60s by Project MAC at MIT on IBM 709,
  then 7094
• Dartmouth Time-Sharing System (DTSS)
• Dartmouth College with General Electric
• Basic language developed for use on DTSS
• TOPS-10 developed by DEC for PDP-10
• TSS/360 developed by IBM for 360/67
• Virtual memory

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Time-Sharing Systems (Cont.)

• MULTICS developed by project MAC (MIT, Bell Labs,
  GE) as successor of CTSS (1964)
• Hardware modified GE635 (called GE645) with
  virtual memory and protection support
• Computing Utility concept
• Segmented virtual memory, linking and loading
  segments on demand, files and segments treated
  the same
• Rings of protection
• Hierarchical file system
• Device independence
• I/O redirection
• Powerful user interface
• Written in a high-level language (PL/1)

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Abstract and Virtual Machines

• T.H.E. developed by Dijkstra at the Technological
  Univ. in Eindhoven, Holland in late 1960s
• Major contributions to OS structuring and process
  synchronization
• Structuring
• Hierarchical structure made of layers
• Each layer, an abstract machine, i.e. apparent
  extension of real machine
• Interacting processes (sharing common resources)
• Semaphores for process synchronization
• Deadlock solutions

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Abstract and Virtual Machines (Cont.)

• TENEX developed by Bolt, Beranek and Newman (BBN)
  for the PDP-10 in early 1970s
• Time-sharing system with an abstract machine
  structure
• CP/CMS (Control Program/Conversational Monitor
  System) developed by IBM Research in Cambridge,
  MA
• Virtual machine concept apparent access to all
  machine features (virtual memory, CPU, I/O
  devices)
• Hardware shared by several OSs (some being
  developed)
• Hardware
• Modified S/360 model 40 (CP/40)
• Modified S/360 model 67 (CP/67)
• Product VM/370 on S/370

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Minicomputer Operating Systems

• Mid-1950s Burroughs E-101, Bendix G-15,
  Librascope LGP-30
• Machine language, no OS
• Early 1960s CDC-160, IBM-1620
• Early 1970s DEC OS-8 and TSS-8 for PDP-8
• Interrupts, DMA
• Disk Operating System for IBM 1800
• Oss named keyboard monitor and real-time
  monitor
• Interactive interface for single user
• Run one program at a time
• Typical application real-time control of lab.
  Operation
• DEC PDP-11 series
• OS (RT-11) simple single user
• RSTS time-sharing system
• RSX-11 real-time executive (multiprogramming,
  memory management, file system, powerful command
  language)

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UNIX

• Early 1970s Bell Labs winds down MULTICS
  participation, Ken Thompson and Dennis Richie
  design a new OS
• Hardware PDP-7 then PDP-11
• Key features
• Hierachical file system
• I/O devices, special cases of files
• Powerful command language Shell
• Redirection input/output from/to any
  sourse/destination in a Shell command
• Concurrent processes with inter-process
  communication
• Languages
• Assembly language initially (PL/I not available
  for PDP)
• Richie developed C (BCPL ? B ? C)
• C compiler for PDP-11 developed
• UNIX re-written in C

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Large Systems Super-Minis and Main Frame Systems

• VAX/VMS for the VAX family from DEC
• Special instructions for OS support
• Extensive system services
• File management techniques
• UNIX implemented on the VAX
• OS/MVS (Multiple Virtual Storage)
• Upgrade of OS/MVT for time-sharing (S/370) based
  on the Time-Sharing Option (TSO) developed for MVT

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Operating Systems for Micros

• Early OSs MITS, IMSAI, Apple, Tandy, Heath
  develop simple OSs (loaders, Basic language)
  running on Intel 8080, Zilogs Z-80, Motorolas
  6800
• CP/M (Control Program for Microprocessors)
• Developed by Gary Killdall at Intel on 8008, then
  8080
• Single user OS
• Simple interactive command interface
• Basic I/O device management
• Floppy disk based file system
• Programming language for microprocessors (PL/M)
• Killdall obtains rights to distribute CP/M, forms
  Digital Research
• CP/M becomes dominant OS for micros

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Operating Systems for Micros (Cont.)

• CP/M limitations
• Limited user interface, file, and device
  management
• No memory management, no multiprogramming
• SCP-DOS from Seattle Computer Products
• Running on Intel 8086 (16-bit)
• New features memory management, timer
  management, interrupt support, sophisticated file
  system
• MS-DOS Upgraded SCP-DOS to run on several
  processors (SCP-DOS acquired by Microsoft)
• PC-DOS Version of MS-DOS selected by IBM to run
  on their PC
• UNIX influence
• MS-DOS Version 2.0 Command interface like
  Shell, hierarchical file system
• Later versions of MS-DOS Multiple users,
  multiple processes

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Major Achievements

• Processes
• Memory Management
• Information protection and security
• Scheduling and resource management
• System structure

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Processes

• Definitions for the term process
• A program in execution
• An instance of a program running on a computer
• The entity that can be assigned to and executed
  on a processor
• A unit of activity characterized by a single
  sequential thread of execution, a current state,
  and an associated set of system resources
• Process components
• An executable program
• Associated data needed by the program
• Execution context of the program or process state
  (e.g., contents of various processor registers,
  priority of the process)

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Memory Management

• Process isolation
• Automatic allocation and management
• Support for modular programming
• Protection and access control
• Long-term storage

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Information Protection and Security

• Access control
• Regulating user access to the total system,
  subsystems, and data
• Regulating process access to various resources
• Information flow control
• Regulating the flow of data within the system and
  its delivery to users
• Certification
• Proving that access and flow control perform
  according to specifications and that they enforce
  desired protection and security policies

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Scheduling and Resource Management

• The operating system
• Manages the various resources main memory space,
  I/O devices, and processors, and
• Schedules their use by the active processes
• The resource allocation and scheduling policy
  must consider
• Fairness
• Give equal and fair access to all processes
• Differential responsiveness
• Discriminate between different classes of jobs
  with different service requirements
• Efficiency
• Maximize throughput, minimize response time, and
  accommodate as many users as possible

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System Structure

• The size and complexity of operating systems have
  significantly increased in time to meet the needs
  of new features and complex hardware
• CTSS 32,000 36-bit words of storage
• OS/360 1 million machine instructions
• MULTICS 20 million instructions
• Windows NT 4.0 16 million lines of code
• Windows 2000 32 million lines of code
• Methods for structuring operating system software
• Modular software
• Hierarchical structure hierarchical layers and
  information abstraction
• View the system as a series of levels
• Each level performs a related subset of functions
• Each level relies on the next lower level to
  perform more primitive functions

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Operating System Design Hierarchy
Level Name Objects Example Operations 13 Shell Use
r programming Statements in shell
language environment 12 User processes User
processes Quit, kill, suspend, resume 11 Directori
es Directories Create, destroy, attach,
detach, search, list 10 Devices External
devices Open, close, read, write printers,
displays and keyboards 9 File
system Files Create, destroy, open,
close read, write 8 Communications Pipes Create
, destroy, open. close, read, write
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Operating System Design Hierarchy

• Level Name Objects Example Operations
• 7 Virtual Memory Segments, pages Read, write,
  fetch
• 6 Local secondary Blocks of data, Read, write,
  allocate, free
• store device channels
• 5 Primitive processes Primitive process, Suspend,
  resume, wait, signal
• semaphores, ready
• list
• 4 Interrupts Interrupt-handling Invoke, mask,
  unmask, retry
• programs
• Procedures Procedures, call Mark stack, call,
  return
• stack, display
• 2 Instruction Set Evaluation stack, Load, store,
  add, subtract
• microprogram
• interpreter
• 1 Electronic circuits Registers, gates, Clear,
  transfer, activate,
• buses, etc. complement

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Characteristics of Modern Operating Systems

• Microkernel Architecture
• Only a few essential functions are assigned to
  the kernel (address space, inter-process
  communication, and basic scheduling)
• Other OS services are provided by processes
  (servers) that run in user mode
• Symmetric MultiProcessing (SMP)
• There are multiple processors
• These processors share same main memory and I/O
  facilities and are interconnected by an internal
  connection scheme
• All processors can perform the same functions

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Characteristics of Modern Operating Systems

• Multithreading process is divided into threads
  that can run concurrently
• Thread
• Dispatchable unit of work
• Includes processor context
• executes sequentially and is interruptable
• Process
• A collection of one or more threads and
  associated system resources

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Characteristics of Modern Operating Systems

• Distributed operating systems
• Provide the illusion of a single main memory and
  single secondary memory space
• State of the art for distributed operating
  systems lags that of uniprocessor and SMP
  operating systems
• Object-oriented design
• Facilitates adding modular extensions to a small
  kernel
• Enables programmers to customize an operating
  system without disrupting system integrity

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Windows 2000 (W2K) Brief History

• MS-DOS and PC-DOS
• DOS 1.0 released in 1981 had 4,000 lines of
  assembly source code, ran in 8Kbytes of memory
  on a 8086
• DOS 2.0 in 1983 ran on the IBM hard-disk based PC
  XT with 24Kbytes of memory resident OS
• Support for hard disk
• Hierarchical directories
• UNIX-like features I/O redirection and
  background printing
• DOS 3.0 in 1984 ran on the PC AT (80286) with
  36Kbytes
• DOS 3.1, also in 1984, provided support for PC
  networking
• DOS 3.3, in 1987 ran on IBM PS/2 with 46Kbytes

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Windows 2000 (W2K) Brief History

• Need for a new operating system
• MS-DOS/PC-DOS did not use the full capabilities
  of the evolving processors 80286, 80386, 80486
  and then Pentium (e.g., extended addressing,
  memory protection)
• To compete with Macintosh, in 1990 Microsoft
  developed a graphical user interface (GUI),
  Windows 3.0, that had to run on top of DOS
• Microsoft and IBM attempt to jointly develop a
  common operating system attempt fails IBM
  develops OS/2 (multitasking, multithreaded),
  Microsoft develops Windows NT

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Windows 2000 (W2K) Brief History

• Windows NT
• NT 3.1 released in 1993
• 32-bit operating system with ability to support
  older DOS and Windows applications, as well as
  provide OS/2 support
• Same GUI as Windows 3.1
• NT 3.x, several versions
• NT 4.0
• Same internal architecture as 3.x
• Same user interface as Windows 98
• Several graphics components moved to NT Executive
  (kernel mode)
• Windows 2000 (W2K)
• Same Executive and microkernel architecture as NT
  4.0
• New services and functions in support of
  distributed processing
• W2K Professional vs. W2K Server

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Single-User and Multi-User Multitasking

• W2K (like OS/2 and MacOS) was design to exploit
  the capabilities of 32-bit microprocessors to
  meet the increasing needs of new applications
• Motivations for multitasking
• Applications have become more complex and
  interrelated (e.g., use of a word processor, a
  drawing program, and a spreadsheet application
  simultaneously for a document)
• Growth of client/server computing system needs
  to support user interaction concurrently with
  inter-processor communication
• W2K Professional supports single-user
  multitasking, while W2K Server supports
  multi-user multitasking

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Windows 2000 Architecture

• Modular structure for flexibility
• Executes on a variety of hardware platforms
• Supports application written for a variety of
  other operating system
• Currently, W2K is only implemented on the
  Pentium/x86 platform
• Separates application-oriented software from
  operating system software
• OS software includes the Executive, the
  microkernel, device drivers, and the hardware
  abstraction layer and runs in kernel mode (access
  to system data and to hardware)
• Application software runs in user mode and has
  limited access to user data

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OS Organization

• Modified microkernel architecture
• Not a pure microkernel Many system functions
  outside of the microkernel run in kernel mode
  (reason performance)
• Highly modular structure
• Each system function is managed by just one
  component of the OS the rest of the OS and all
  applications access that component using a
  standard interface
• Key system data can only be accessed through the
  appropriate function
• Any module can be removed, upgraded, or replaced
  without rewriting the entire system

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OS Organization Layered Structure

• Hardware Abstraction Layer (HAL) Maps between
  generic hardware commands and responses and those
  unique to a specific platform
• Microkernel Consists of the most used and most
  fundamental components of the OS. Manages thread
  scheduling, process switching, exception and
  interrupt handling, and multiprocessor
  synchronization. It does not run in threads not
  preemptable nor pageable
• Device Drivers File system and hardware device
  drivers that translate user I/O function calls
  into specific hardware device I/O requests
• I/O Manager Dispatches requests to appropriate
  device drivers
• Object Manager Creates, manages, and deletes
  Executive objects
• Security reference monitor Enforces
  access-validation and audit-generation rules
• Process/thread manager Creates/deletes objects
  and tracks process and thread objects
• Local Procedure Call (LPC) Facility Enforces
  client/server relationship between applications
  and executive subsystems within a single system

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OS Organization Layered Structure Cont.)

• Virtual memory manager Maps virtual addresses
  in processs address space to physical pages in
  memory
• Cache manager Improves performance of file-based
  I/O (read from cache, defer write)
• Windows/graphics modules Creates the
  windows-oriented screen interface and manages the
  graphics devices
• User processes
• Special system support processes Services not
  included in W2K (e.g., logon process)
• Server processes Other W2K services (e.g., event
  logger)
• Environment subsystems Supported subsystems are
  Win32, Posix, and OS/2
• User applications Can be of five types Win32,
  Posix, OS/2, Windows 3.1 or MS-DOS

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Client/Server Model

• Operation
• A client (e.g., application program or another OS
  module) requests a service by sending a message
• Message routed through the Executive to
  appropriate server
• Server performs requested operation and returns
  results or status with another message
• Message routed through Executive back to client
• Advantages of client/server architecture
• Simplifies the Executive possible to construct a
  variety of APIs
• Improves reliability clients cannot not directly
  access hardware
• Provides a uniform means fro applications to
  communicate via LPC
• Provides base for distributed computing

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Threads and SMP

• W2K features that support threads and SMP
• OS routines can run on any available processor
  and different routines can execute simultaneously
  on different processors
• Multiple threads of execution within a single
  process may execute on different processors
  simultaneously
• Server processes may use multiple threads to
  process requests from many clients simultaneously
• W2K provides mechanisms for sharing data and
  resources between processes and flexible
  interprocess communication capabilities

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UNIX

• Brief history (cont.)
• First widely available version outside Bell Labs
  was Version 6, in 1976
• Version 7, released in in 1978, is the ancestor
  of modern UNIX systems
• Most important non-ATT development done at U. of
  C. at Berkeley, called UNIX BSD, running first on
  PDP, then VAX
• In 1982, Bell Labs combined several ATT versions
  into a system marketed as UNIX System III
• A number of new features were developed to
  produce UNIX System V
• Traditional UNIX systems System V Release 3
  (SVR3), 4.3BSD
• Traditional UNIX system characteristics
• Hardware is surrounded by the operating-system
  called kernel
• UNIX comes with a number of user services and
  interfaces (I.e., shell, other interface
  software, and the components of the C compiler)
• Runs on a single processor and has limited
  protection capabilities

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UNIX
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Modern UNIX Systems

• System V Release 4 (SVR4)
• Developed jointly by ATT and Sun Microsystems,
  combined features from SVR3, 4.3BSD, Microsoft
  Xenix System V, and SunOS
• New features real-time processing support,
  process scheduling classes, dynamically allocated
  data structures, virtual memory management,
  virtual file system, and a preemptive kernel
• Runs on machines ranging from 32-bit
  microprocessors up to supercomputers
• Solaris 2.x
• Suns SVR4-based UNIX release
• Provides a number of advanced features fully
  preemptable, multithreaded kernel, full support
  for SMP, and an object-oriented interface to file
  systems
• Is is the most widely used and most successful
  commercial UNIX implementation
• 4.4BSD
• Linux

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Modern UNIX Systems (Cont.)

• 4.4BSD
• Berkeley Software Distribution (BSD) series of
  UNIX releases has played a key role in the
  development of OS theory
• Most enhancements to UNIX first appeared in BSD
  versions
• 4.xBSD is widely used in academic installations
  and has served as the basis of a number of
  commercial UNIX products
• 4.4BSD is the final version of BSD to be released
  by Berkeley and includes a new virtual memory
  system and changes in the kernel structure
• Linux

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Modern UNIX Systems (Cont.)

• Linux
• Started as a UNIX variant for the IBM PC
  architecture written by Linus Torvalds and posted
  on Internet in 1991
• A large number of collaborators contributed to
  the development of Linux under the control of
  Torvalds
• Linux is free and the source code is available
  under the auspices of the Free Software
  Foundation (FSF)
• Today, Linux is a full-featured UNIX system
  running on a variety of platforms
• Linux key advantages
• Modular structure kernel organized as a
  collection of loadable modules a module can be
  loaded and linked into the kernel while the
  kernel is in memory and executing
• With source code available, vendors can tweak
  applications and utilities to meet specific
  requirements