Transcript Chapter 1 Introduction

Chapter 1
Introduction
Outline
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What is an operating system?
History of operating systems
Categories of operating systems
Computer hardware review
Operating system concepts
System calls
Operating system structure
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Computer As A Complex System
• Many resources
– Hardware: processors, memory, disks, printers,
keyboard, display, network interfaces, …
– Software: office tools, multimedia players, …
• Many tasks
– Surfing web, handling emails, solving equations,
playing music, …
• Many users
– Playing with computer should be easy
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Read From Diskette …
• Basic commands: read and write
– 13 parameters, packed into 9 bytes
• Controller chips
– 23 status and error field
• Motor switch: on/off
– Don’t leave motor on too long!
• Do you want to program the hardware
directly?
– A simpler interface is needed!
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Why A Simple Interface Possible?
• Many tedious details can be handled by
default
– They are out of the user’s interest
• Only some key features are important
– Examples: file name, length of the file, etc
• A simple interface
– Present key features to programmer
– Hide many tedious details
– Meet requirements from many programs
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OS As An Extended Machine
• Extended machine/virtual machine
– Easier to program than the underlying hardware
– Provide a variety of services (system calls)
• Trade-off
– Higher efficiency in program development and
system management
– Less efficiency in program execution
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Programs Without Coordination
• Three programs want to output to a printer
– A chaos if no coordination
• How to coordinate?
– Buffer outputs on disk
– Copy complete outputs to printer one by one
• Do you want to coordinate everything in a
computer system?
– A resource manager is needed!
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OS As A Resource Manager
• Multiplexing (sharing) resources
– In time
• Users/programs take turns using resources
• CPU, printers, etc.
– In space
• Users/programs get parts of resources
• Main memory, disk, etc.
• Issues about a good manager
– Fairness, efficiency, protection, …
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What Is An Operating System?
Provide user
programs with
a simpler
Banking
system
interface
Airline
reservation
Compilers
Editors
Web
browser
Application
programs
Command
interpreter System
programs
Operating system
Machine language
Microarchitecture
Physical devices
Hardware
Manage
resources
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Outline
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What is an operating system?
History of operating systems
Categories of operating systems
Computer hardware review
Operating system concepts
System calls
Operating system structure
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History of Operating Systems
• OS and architecture of computers
– Computer evolves  so does OS
– To provide better service  OS has impact on
computer design
• Keep evolving through years
– Four generations so far
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The First Generation Computer
• Vacuum tubes and plugboards
– 1944-1955
• Applications:
– Straightforward numerical calculations
• Scenario
– Single group of people designed, built,
programmed, operated and maintained a
machine
– All in absolute machine language
• No operating system
– The people maintaining the computers are OS?!
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The Second Generation OS
• Transistors and batch systems
– 1955-1965
• Applications
– Scientific and engineering calculation
IBM 1401
IBM 7094
Read batch
of jobs onto
tape
Cards from
programmers
Input tape
Do computing
IBM 1401
Print out
Output
tape
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Ancestor of Today’s OS
• Scenario: batch systems
– Fortran
• Operating system
– Read a job from tape  run the job  write
output onto a second tape
– Load next job
• Examples:
– FMS, IBSYS
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The Third Generation OS
• Features: ICs and multiprogramming
– 1965-1980
• Applications
– Numerical calculations in science & engineering
• Word-oriented, large-scale scientific computers
– Massive commercial data processing
• Character-oriented, commercial computers
– Can we solve both problems at a single stroke?
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System/360 and OS/360
• One family
– A series of software-compatible machines
– Different only in price and performance
– Capable of both scientific & commercial apps
• Problems
– Dinosaurs: huge operating systems
– Millions of instructions, thousands of developers
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Key Advances in 3rd Gen OS
• Multiprogramming
– Run job 2 while job 1 waiting for I/O
– Keep CPU busy
• Spooling
– Read job from cards to disk asap
– Load new jobs from disk whenever old job done
• Time sharing
– CPU is allocated in turn
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Milestones
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IBM OS/360
M.I.T. CTSS
M.I.T. MULTICS
Ken Thompson UNIX
– AT&T UNIX System V
– UC Berkeley UNIX BSD
– IEEE POSIX
– Andrew S. Tanenbaum MINIX
– Linus Torvalds Linux
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The Fourth Generation OS
• Personal computers
– 1980-now
– An individual has her own computer
• Milestones
– Kildall CP/M for Intel 8080, Z80
– MS-DOS/BASIC for IBM PC
– Engelbart GUI
– MS Windows, Windows NT
– UNIX X Windows
– Network & distributed operating systems
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Outline
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•
•
•
•
What is an operating system?
History of operating systems
Categories of operating systems
Computer hardware review
Operating system concepts
System calls
Operating system structure
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Categories of Operating Systems
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Mainframe operating systems
Server operating systems
Multiprocessor operating systems
Personal computer operating systems
Real-time operating systems
Embedded operating systems
Smart card operating systems
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Mainframe Operating Systems
• Why mainframe computers
– Strong I/O capability, e.g., 1000 disks, TB space
– High-end servers
• Features of OS
– Batch
– Transaction processing
– Timesharing
• Example: IBM OS/390
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Server Operating Systems
• Hardware platforms
– Very large personal computers or workstations
• Services
– Printing
– File accessing
– Web
• Examples
– UNIX, Windows 2000, Linux
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Multiprocessor Operating Systems
• Multiple CPUs within a single system
– Parallel computers: loosely coupled
– Multi-computers: tightly coupled
– Multiprocessors: share memory
• Features of OS
– Communications and connectivity
– Variations of the server operating systems
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Personal Computer OS
• Good interface to a single user
– Word processing, spreadsheets, internet
access, …
• Examples
– Windows 98, Windows 2000
– Macintosh operating system
– Linux
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Real-time Operating Systems
• Having time as a key parameter
– Industrial process control systems
• Hard/soft real-time systems
– Hard real-time system: actions absolutely must
occur at a certain moment
• Robot at an assembly line
– Soft real-time system: missing an occasional
deadline is acceptable
• Digital audio or multimedia systems
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Embedded Operating Systems
• Very small computers
– Palmtop/PDA
– Device controllers
• Features of OS
– Kind of real-time systems
– Restrictions in size, memory, power, …
• Example: PalmOS, Windows CE
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Smart Card Operating Systems
• CPU chips on credit card-sized devices
– Proprietary systems
• Features
– Java oriented
– Multiprogramming for Java applets
– Resource management and protection
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Outline
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What is an operating system?
History of operating systems
Categories of operating systems
Computer hardware review
Operating system concepts
System calls
Operating system structure
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Components of a Computer
• System bus: connect all components
CPU
Memory
Monitor
Keyboard
Video
controller
Keyboard
controller
Floppy
disk
driver
Hard
disk
driver
Floppy
disk
controller
Hard disk
controller
Bus
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CPU
• Registers
– General registers
– Program counter: pointer to next instruction
– Stack pointer: to the top of current memory
– PSW: condition code bits
• Basic model
– Fetching instruction  decoding  executing
• Execution image: a snapshot of registers
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Pipeline and Superscalar
• Pipeline: overlap instruction execution
Fetch
unit
Decode
unit
I1
Execute I
2
unit
I3
• Superscalar: multiple execution units
Fetch
unit
Fetch
unit
Decode
unit
Decode
unit
Execute unit
Holding
buffer
Execute unit
Execute unit
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System Calls
• Two modes in CPU
– Kernel mode: full capability
– User mode: disallow I/O, memory protection
• System calls: get OS service for user
program
– Traps: OS gets control
– TRAP instruction switches from user mode to
kernel mode and starts OS
– When the work done, control is returned to user
program
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Memory Hierarchy
Typical access
time
Typical capacity
1 nsec
Register
<1 KB
2 nsec
Cache
1 MB
10 nsec
Main memory
64-512 MB
10 msec
Magnetic disk
5-50 GB
100 sec
Magnetic tape
20-100 GB
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Nonvolatile RAM
• ROM
– Programmed once, cannot be changed
afterward
– Fast and inexpensive
– Boot strap loader, fixed programs
• EEPROM and flash RAM
– Rewritable
• CMOS
– Volatile, one battery lasts for several years
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Memory Management
• Hold multiple programs in main memory
– Improve CPU utilization
• Problems
– Protection
• Program A is not allowed to fetch data within program
B
– Relocation
• Each program starts from logical address 0
• How to load and allocate them into main memory?
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Base/limit Registers
• Base register
0xFFFFFFF
– Point to the start of a program
– Its content is added to every program
address
User
program
and data
• Limit register
– Record the size of program + data
– Limit of addresses
Limit
User
program
and data
• Virtual address  physical address
Base
– Base = 4096, limit = 6114
– Virtual addr = 2000  physical addr =
6096 < limit, legal!
• MMU: memory management unit
Operating
system
0
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Registers
when
running
program 2
Split Program and Data
• Why: multiple users
may run a same
program
• How: base/limit
registers for program
and data, respectively
Registers
when
running
program 1
Limit-1
Base-1
Limit-2
Base-2
• Overhead of switching:
context switch
Limit-2
User-2
data
Base-2
User
program
Limit-1
User-1
data
Base-1
Operating
system
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I/O Devices
• Controller: physically controls the devices
– Devices are diverse and complicated
• Device driver: software talks to a controller
– Depends on operating systems
Operating system
• Installation of drivers
– Relink kernel with new driver, reboot
driver
– Register driver in system file, reboot controller
– Install on-the-fly, NO reboot
device
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Busy Waiting I/O
User program
Kernel
Driver
I/O device
Issue a system call
Call driver
Start I/O
Polling
Do I/O
Put data
Return control to
caller
Continue
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I/O by Interrupt
• Driver programs controller by writing its device registers.
Controller starts device
• Controller finishes reading/writing, and then signals the
interrupt controller
• If interrupt controller can accept the interrupt, it informs
CPU
• Interrupt controller puts the number of device on the bus,
CPU read it
Disk drive
CPU
Interrupt controller
Disk controller
3
4
2
1
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Interrupt Processing
Current instruction
Next instruction
1. Interrupt
3. Return
2. Dispatch to
handler
Interrupt
handler
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Direct Memory Access (DMA)
User program
Kernel
I/O device & memory
Issue a system call
Set up DMA chip
Suspended
Run other
programs
I/O directly
Issue interrupt when
finish
Set the program
status as “ready”
Ready to continue
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Advanced Computer With Multiple Buses
Cache bus Local bus
Level 2
cache
CPU
Memory bus
PCI
bridge
Main
memory
PCI bus
SCSI
SCSI bus Mouse
Modem
USB bus
ISA
USB
bridge
Keyboard
Sound card
IDE bus
IDE
disk
Available
Graphics PCI slot
adaptor
ISA bus Monitor
Printer
Available
ISA slot
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Plug and Play
• Problems without plug and play
– Each I/O card has a fixed interrupt level/address
– When new card comes  conflict level/address
– Use switches/jumpers to select good
level/address  more than an art
• How plug and play
– System collects info/assign level/address for I/O
devices
– BIOS does major work
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Warm-up
• Operating system = extended (virtual)
machine + resource manager
• Hardware evolving  operating system
evolving
– 4 generations
– Various hardware platform  various OS
• Important components of a computer
– CPU, bus, memory, I/O
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Outline
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What is an operating system?
History of operating systems
Categories of operating systems
Computer hardware review
Operating system concepts
System calls
Operating system structure
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Process
• A program in execution
– Address space: a list of memory locations the
process can read/write
– Registers, e.g., PC, SP, …
• Examples
– Two processes running two programs: Word,
Excel
– Two processes running the same program:
multiple web-browsers in a PC
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Information About Processes
• Process table in operating systems
– Registers, etc.
• Core image: suspended process address
space
• Process information = Process table entry +
core image
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Process Management System
Calls
• Create a new (child) process
– Process tree
A
• Interprocess communication
B
– Communication
– Synchronization
• Request/release memory
• Alarm signal
D
E
C
F
– E.g., remote communication
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Users and Processes
• User group: a group of users
– GID
• Users are identified by UID
– Superuser/system administrator
• One user can run many processes
– Processes from one user share same UID
– Processes are identified by PID
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Deadlocks
No one can make
any progress!
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Deadlock in Computer
Time Process 1
Process 2
1 Get CD-recorder
2
Get tape drive
3 Wait for tape drive
4
Wait for CD recorder
Deadlock!
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Memory Management
• Sharing main memory among processes
– Protection
• Handling virtual memory larger than physical
memory
– Reallocation: map memory space to main
memory and disk
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Files and Directories
• Directory: hierarchy of files
Root
Students
Robert
Matty
Courses
Faculty
Leo
Papers
Prof. Brwon
Grants
Prof. Green
Prof. White
Committees
Path /Faculty/Prof.Brown/Courses/CS105
CS101
CS105
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Mounted File System
Root
Root
a
b
a
c
b
d
Floppy
x
c
d
x
y
y
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Model I/O Devices As Files
• Block special files: a collection of randomly
addressable blocks, e.g., disks
• Character special files: devices
accept/output character stream, e.g.,
printers, modems
• Pipe: pseudofile connecting two processes
Process
Process
Pipe
A
B
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Outline
•
•
•
•
•
•
•
What is an operating system?
History of operating systems
Categories of operating systems
Computer hardware review
Operating system concepts
System calls
Operating system structure
58
System Calls
• Interface between OS and user programs
• Similar underlying concepts
– Details vary from OS to OS
• A procedure library for programming
languages
– Like making a special procedure call
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System Call Read
• A call in C: count=read(fd, buffer, nbytes);
– Count  # of bytes really read
– If failed, count  -1
– errno  error number
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Making System Call read()
count=read(fd, buffer, nbytes);
Count  # of bytes
really read
If failed, count  -1,
errno  error
number
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POSIX System Calls: Process
Management
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Fork()
Waitpid(pid, &statloc, options)
Execve(name, argv, environp)
Exit(status)
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POSIX System Calls: File
Management
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Open(file, how, …)
Close(fd)
Read(fd, buffer, nbytes)
Write(fd, buffer, nbytes)
Lseek(fd, offset, whence)
Stat(name, &buf)
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POSIX System Calls: Directory
and File System Management
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Mkdir(name, mode)
Rmdir(name)
Link(name1, name2)
Unlink(name)
Mount(special, name, flag)
Umount(special)
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POSIX System Calls:
Miscellaneous
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Chdir(dirname)
Chmod(name, mode)
Kill(pid, signal)
Time(&seconds)
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Win32 API Calls
Win32
CreateProcess
WaitForSigleObject
(none)
ExitProcess
CreateFile
CloseHandle
ReadFile
WriteFile
SetFilePointer
GetFileAttributesEx
UNIX
fork
waitpid
execve
exit
open
close
read
write
lseek
stat
Win32
CreateDirectory
RemoveDirectory
(none)
DeleteFile
(none)
(none)
SetCurrentDirectory
(none)
(none)
GetLocalTime
UNIX
mkdir
rmdir
link
unlink
mount
umount
chdir
chmod
kill
time
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Outline
•
•
•
•
•
•
•
What is an operating system?
History of operating systems
Categories of operating systems
Computer hardware review
Operating system concepts
System calls
Operating system structure
67
Monolithic Systems
• No structure as a good structure
– OS: a collection of procedures
• Three layers of procedures
Invoke requested
service procedure
Carry out
system calls
Help service
procedures
Main procedures
Service
procedures
Utility procedures
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Relation Among Procedures
• A main program
– Involve the requested service procedures
• A set of service procedures
– Carry out the system calls
• A set of utility procedures
– Help the service procedures
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Layered Systems
THE system
Layer
Function
5
The operator
4
User programs
3
Input/output management
2
Operator-process communication
1
Memory and drum management
0
Processor allocation and multiprogramming
professor
MULTICS
students
System calls
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Virtual Machines
• Virtual machine monitor (VM/370)
– Multiprogramming by multiple virtual machines
– Each virtual machine is exact copies of 370
• Operating systems run on virtual machines
– Two level traps
I/O incrustations here
Trap here
CMS
CMS
CMS
VM/370
370 bare hardware
System calls here
Trap here
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Exokernels
• Give each user a clone of actual computer,
but with a subset of the resources
• Two levels
– Exokernel: allocate/maintain resources to virtual
machines
– OS: run on virtual machines
• Advantages
– Save a layer of mapping
– Separate multiprogramming from user OS code
with less overhead
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Client-server Model
• Move code from kernel up into higher layers
– Kernel  minimal microkernel
– Implement most of the OS in user processes
Client
Client Process Terminal
process process server
server
…
File
server
Memory
server
Microkernel
User
mode
Kernel
mode
Client obtains service by sending
messages to server processes
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Advantages of Client-server Model
• Robust
– A bug may cause crash within a module only
• Adaptable
– Easy to implement in distributed systems
Machine 1
Machine 2
Machine 3
Machine 4
Client
File server
process server
Terminal server
kernel
kernel
kernel
kernel
Network
Message from client to server
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Summary
• Operating systems = resource managers +
extended machines
• Operating systems evolve as hardware evolving
• Review of computers hardware for good
understanding of operating systems
• Basic concepts of OS: processes, memory
management, I/O management, file system,
security
• System calls as heart of operating systems
• Structures of operating systems
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