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Operating System Overview. Chapter 2. Announcements. Homework 0 will be posted today, due next Wednesday (September 17) at noon Project requires the following book OSP An Environment for Operating System Project by Kifer and Smolka, Addison Wesley, 1991

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announcements
Announcements
  • Homework 0 will be posted today, due next Wednesday (September 17) at noon
  • Project requires the following book
    • OSP An Environment for Operating System Project by Kifer and Smolka, Addison Wesley, 1991
    • first project assignment will be posted next week
basic computer structure
Basic computer structure

Memory

CPU

memory bus

I/O bus

disk

Net interface

memory caches
Memory caches
  • motivated by the mismatch between processor and memory speed
  • closer to the processor than the main memory
  • smaller and faster than the main memory
  • act as “attraction memory”: contains the value of main memory locations which were recently accessed (temporal locality)
  • transfer between caches and main memory is performed in units called cache blocks/lines
  • caches contain also the value of memory locations which are close to locations which were recently accessed (spatial locality)
cache design issues
Cache design issues
  • cache size and cache block size
  • mapping: physical/virtual caches, associativity
  • replacement algorithm: LRU
  • write policy: write through/write back

cpu

word transfer

cache

block transfer

main

memory

memory hierarchy
Memory Hierarchy
  • decrease cost per bit
  • decrease frequency of access
  • increase capacity
  • increase access time
  • increase size of transfer unit

cpu

word transfer

cache

block transfer

main memory

page transfer

disks

data transfer on the bus
Data transfer on the bus
  • cache-memory: cache misses, write-through/write-back
  • memory-disk: swapping, paging, file accesses
  • memory-Network Interface : packet send/receive
  • I/O devices to the processor: interrupts

CPU

Memory

cache

memory bus

I/O bus

disk

Net interface

direct memory access dma
Direct Memory Access (DMA)
  • bulk data transfer between memory and an I/O device (disk, network interface) initiated by the processor
  • address of the I/O device
  • starting location in memory
  • number of bytes
  • direction of transfer (read/write from/to memory)
  • processor interrupted when the operation completes
  • bus arbitration between cache-memory and DMA transfers
  • memory cache must be consistent with DMA
multiprocessors
Multiprocessors
  • simple scheme: more than one processor on the same bus
  • memory is shared among processors-- cache consistency
  • bus contention increases -- does not scale
  • alternative (non-bus) system interconnect -- expensive
  • single-image operating systems

CPU

CPU

Memory

cache

cache

memory bus

I/O bus

disk

Net interface

multicomputers
Multicomputers
  • network of computers: “share-nothing” -- cheap
  • communication through message-passing: difficult to program
  • challenge: build efficient shared memory abstraction in software
  • each system runs its own operating system

CPU

CPU

Memory

Memory

cache

cache

memory bus

memory bus

I/O bus

I/O bus

network

disk

Net interface

disk

Net interface

operating system
Operating System
  • A program that controls the execution of application programs
  • An interface between applications and hardware
operating system objectives
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
services provided by the operating system
Services Provided by the Operating System
  • Program development
    • Editors and debuggers
  • Program execution
  • Access to I/O devices
  • Protected access to files
services provided by the operating system15
Services Provided by the Operating System
  • Error detection and response
    • internal and external hardware errors
      • memory error
      • device failure
    • software errors
      • arithmetic overflow
      • access forbidden memory locations
    • error recovery
services provided by the operating system16
Services Provided by the Operating System
  • Accounting
    • collect statistics
    • monitor performance
    • used to anticipate future enhancements
    • used for billing users
operating system17
Operating System
  • Functions same way as ordinary computer software
    • It is a program that is executed to service requests coming
      • from applications: system calls
      • from the hardware: interrupts
  • Operating system services the request, then relinquishes control of the processor to execute other programs
kernel
Kernel
  • Portion of operating system that is resident in main memory
  • Contains a machine-independent part (code for system calls) and a machine-dependent part (device drivers)
  • Maintains the OS state
  • Executes in privileged/supervisor mode
evolution of operating systems
Evolution of Operating Systems
  • Serial Processing
    • No operating system
    • Machines run from a console with display lights and toggle switches, input device, and printer
    • Schedule tome
    • Setup included loading the compiler, source program, saving compiled program, and loading and linking
evolution of operating systems21
Evolution of Operating Systems
  • Simple Batch Systems
    • Monitors
      • Software that controls the running programs
      • Batch jobs together
      • Program branches back to monitor when finished
      • Resident monitor is in main memory and available for execution
job control language jcl
Job Control Language (JCL)
  • Special type of programming language
  • Provides instruction to the monitor
    • what compiler to use
    • what data to use
hardware features
Hardware Features
  • Memory protection
    • do not allow the memory area containing the monitor to be altered
  • Timer
    • prevents a job from monopolizing the system
hardware features24
Hardware Features
  • Memory protection
    • do not allow the memory area containing the monitor to be altered
  • Timer
    • prevents a job from monopolizing the system
uniprogramming
Uniprogramming
  • Processor must wait for I/O instruction to complete before preceding
multiprogramming
Multiprogramming
  • When one job needs to wait for I/O, the processor can switch to the other job
time sharing
Time Sharing
  • Using multiprogramming to handle multiple interactive jobs
  • Processor’s time is shared among multiple users
  • Multiple users simultaneously access the system through terminals
main os concepts
Main OS Concepts
  • Processes
  • Memory Management
  • Information protection and security
  • Scheduling and resource management
  • System structure
processes
Processes
  • 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
difficulties with designing system software
Difficulties with Designing System Software
  • Improper synchronization
    • ensure a process waiting for an I/O device receives the signal
  • Failed mutual exclusion
  • Nondeterminate program operation
    • program should only depend on input to it, not relying on common memory areas
  • Deadlocks
process
Process
  • Consists of three components
    • An executable program
    • Associated data needed by the program
    • Execution context of the program
      • All information the operating system needs to manage the process
memory management
Memory Management
  • Process isolation
  • Automatic allocation and management
  • Support for modular programming
  • Protection and access control
  • Long-term storage
virtual memory
Virtual Memory
  • Allows programmers to address memory from a logical point of view
file system
File System
  • Implements long-term store
  • Information stored in named objects called files
paging
Paging
  • Allows process to be comprised of a number of fixed-size blocks, called pages
  • Virtual address is a page number and an offset within the page
  • Each page may be located any where in main memory
  • Real address or physical address in main memory
information protection and security
Information Protection and Security
  • Access control
    • regulate user access to the system
  • Information flow control
    • regulate flow of data within the system and its delivery to users
  • Certification
    • proving that access and flow control perform according to specifications
scheduling and resource management
Scheduling and Resource Management
  • Fairness
    • give equal and fair access to all processes
  • Differential responsiveness
    • discriminate between different classes of jobs/users
  • Efficiency
    • maximize throughput, minimize response time, and accommodate as many uses as possible
system structure
System Structure
  • 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
  • This decomposes a problem into a number of more manageable subproblems
operating system design hierarchy
Operating System Design Hierarchy
  • Level Name Objects Example Operations
  • 4 Interrupts Interrupt-handling Invoke, mask, unmask, retry
  • programs
  • Procedures Procedures, call stack, Mark stack, call, return
  • display
  • 2 Instruction Set Evaluation stack, micro- Load, store, add, subtract
  • program interpreter, branch
  • scalar and array data
  • 1 Electronic circuits Registers, gates, buses, Clear, transfer, activate,
  • etc. complement
operating system design hierarchy46
Operating System Design Hierarchy

Level Name Objects Example Operations

7 Virtual Memory Segments, pages Read, write, fetch

6 Local secondary Blocks of data, device Read, write, allocate, free

store channels

5 Primitive processes Primitive process, Suspend, resume, wait, signal

semaphores, ready

list

operating system design hierarchy47
Operating System Design Hierarchy

Level Name Objects Example Operations

13 Shell User programming Statements in shell language

environment

12 User processes User processes Quit, kill, suspend, resume

11 Directories Directories Create, destroy, attach, detach,

search, list

10 Devices External devices, such Open, close,

as printer, displays read, write

and keyboards

9 File system Files Create, destroy, open, close

read, write

8 Communications Pipes Create, destroy, open. close,

read, write

traditional os structure
Traditional OS structure
  • monolithic/layered systems
  • one/N layers all executed in “kernel-mode”
  • good performance but rigid

user

process

user

system calls

memory

system

file

system

OS kernel

hardware

characteristics of modern operating systems
Characteristics of Modern Operating Systems
  • Microkernel architecture
    • assigns only a few essential functions to the kernel
      • address space
      • interprocess communication (IPC)
      • basic scheduling
micro kernel os
Micro-kernel OS

memory

server

client

process

file

server

user mode

IPC

micro-kernel

hardware

  • client-server model, IPC between clients and servers
  • the micro-kernel provides protected communication
  • OS functions implemented as user-level servers
  • flexible but efficiency is the problem
  • easy to extend for distributed systems
extensible os kernel
Extensible OS kernel

process

process

user mode

my

memory

service

default

memory

service

extensible kernel

hardware

  • user processes can load customized OS services into the kernel
  • good performance but protection and scalability become problems
characteristics of modern operating systems52
Characteristics of Modern Operating Systems
  • Multithreading
    • process is divided into threads that can run simultaneously
  • Thread
    • dispatchable unit of work
    • executes sequentially and is interruptable
  • Process is a collection of one or more threads and associated system resources
characteristics of modern operating systems53
Characteristics of Modern Operating Systems
  • Symmetric multiprocessing
    • there are multiple processors
    • these processors share same main memory and I/O facilities
    • All processors can perform the same functions
characteristics of modern operating systems54
Characteristics of Modern Operating Systems
  • Distributed operating systems
    • provides the illusion of a single main memory and single secondary memory space
    • used for distributed file system
slide55
UNIX
  • Hardware is surrounded by the operating-system
  • Operating system is called the kernel
  • Comes with a number of user services and interfaces
    • shell
    • C compiler
modern unix systems
Modern UNIX Systems
  • System V Release 4 (SVR4)
  • Solaris 2.x
  • 4.4BSD
  • Linux