Download CSE 30341

1/13/16
CSE30341
Opera+ngSystemPrinciples
Lecture2–Introduc5on–Con5nued
Recap–LastLecture
•  Whatisanopera+ngsystem&kernel?
•  Whatisaninterrupt?
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OS-Kernel
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OS-Kernel
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SystemArchitecture
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Interrupt
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Interrupt
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Interrupt
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Input/Output–I/O
•  Communica+onbetweenCPUand“outside
world”:
–  Storage
–  Network
–  Keyboard/mouse
–  Display
–  Printer
–  …
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Input/Output–I/O
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Interac+ngwithI/O
•  System-controlled:
–  “Writethischunkofdatatoblock8,783,486”
–  “Pleasegivemethedatafromblocks7,345,286–
7,345,289”
•  Externalevents(systemreacts):
–  Theuserispressingtheshi_key
–  Block3,285,001appearstobebad
–  Dataarrivedoveranetworkconnec+on
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Interac+ngwithI/O
•  Responsibili+esofOS:
–  Hide peculiarities of hardware devices from
the user
–  Manage hardware devices (“resources”)
efficiently
–  Prevent intentional/unintentional misuse
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Interac+ngwithI/O
•  Application requests I/O from OS
–  Uses specific interface: system calls
–  Blocking: application will wait until I/O
complete
–  Non-blocking: application will do something
else in the meantime (and receive notification
from OS when I/O complete)
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Direct Memory Access (DMA)
•  CPUresponsiblefordatamovingto/fromI/Odevices
•  Alterna+ve:letaseparatecontrollerdoit(DMA)
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DMAController
I/O
DeviceD6
Memory
CPU
Pleasecopy500bytes
ofdatafromD6tomemory
loca+on0x8570000and
interruptmewhenyouare
done
DMA
Controller
vs.
ReadfromD6
WritetoMemory
ReadfromD6
WritetoMemory
….
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Storage Structure
•  Main memory – only large storage media that the CPU
can access directly
–  Random access memory
–  Volatile
•  Secondary storage – extension of main memory that
provides large nonvolatile storage capacity
–  Magnetic disks – rigid metal or glass platters covered with
magnetic recording material
•  Disk surface - tracks, subdivided into sectors
•  The disk controller determines the logical interaction between
the device and the computer
–  Solid-state disks – faster than magnetic disks, nonvolatile
•  Various technologies
•  Becoming more popular
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Storage-Device Hierarchy
registers
cache
main memory
solid-state disk
magnetic disk
optical disk
magnetic tapes
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Storage Hierarchy
•  Storage systems organized in hierarchy
–  Size
–  Speed
–  Cost
–  Volatility
•  Caching – leverage faster storage
system; higher layer can be cache for
lower layer
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Caching
•  One of the most important principles in systems
•  Information in use copied from slower to faster
storage temporarily
•  Faster storage (cache) checked first to determine
if information is there
–  If it is, information used directly from the cache (fast)
–  If not, data copied to cache and used there
•  Cache smaller than storage being cached
–  Cache management important design problem
–  Cache size and replacement policy
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Computer-System Architecture
•  General-purpose processors (CPU) versus
special-purpose processors (controllers)
•  Multiprocessor systems are now typical
–  Parallel systems, tightly-coupled systems
–  Advantages include:
1.  Increased throughput
2.  Economy of scale
3.  Increased reliability – graceful degradation or fault
tolerance
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Symmetric Multiprocessing (SMP)
Architecture
UMA–UniformMemoryAccess
•  Allsharethesamememoryonthesamemachine,samecosttoaccess.
•  Mayhaveaprivatecache
NUMA–Non-uniformMemoryAccess
•  Eachprocessorhasitsownmemory
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Multi-Core Design
•  Multiple “cores” on same chip
–  On-chip communication is fast
–  Power consumption can be reduced
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Clustered Systems
•  Like multiprocessor systems, but multiple
systems working together
–  Connected via LAN (local-area network)
–  Storage often shared via SAN (storage-area
network)
–  Main reasons:
•  High availability
–  Asymmetric clustering (one machine in hot-standby mode)
–  Symmetric clustering (multiple machines running and
monitoring each other)
•  High performance (HPC)
–  Applications must be written to exploit parallelization
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Clustered Systems
computer
interconnect
computer
interconnect
computer
storage area
network
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Operating Systems Concepts
A von Neumann architecture
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Opera+ngSystemsConcepts
•  Mul5programming(efficiency)
–  SingleusercannotkeepCPUandI/Odevicesbusy
atall+mes
–  Jobs(code&data)organizeds.t.CPUalwayshas
atleastonetoexecute
–  Subsetofjobskeptinmemory
–  Whenajobhastowait(e.g.,forI/O),theOS
switchestoanotherjob
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Memory Layout for Multiprogrammed System
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Opera+ngSystemsConcepts
•  Timesharing(mul5tasking):
–  Switchingbetweenjobshappenssofrequentlythat
userscaninteractwitheachjobwhileitisrunning:
interac5vecompu5ng
–  Response5me(e.g.,<1second)
–  Eachuserhasatleast1programexecu+nginmemory
(process)
–  Ifseveraljobsreadytorunatthesame+me:CPU
scheduling
–  Ifprocessesdon’tfitintomemory:swapping
–  Virtualmemoryallowsofexecu+onofpar+ally
loadedprocesses
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Opera+ngSystemsConcepts
•  Accesstoresourcesneedstobecontrolled:
–  Simultaneousaccess
–  Unauthorizedaccess
–  “Improper”access(e.g.,toolong)
•  Dual-modeopera5ngsystems
–  Usermode(applica+on)
–  Kernelmode(OSandprivilegedinstruc+ons)
–  Modebitindicatescurrentmode(0=kernel)
–  Transi+onviasystemcalls
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From User to Kernel Mode
•  Timer to prevent infinite loop / process hogging resources
– 
– 
– 
– 
Set interrupt after specific period
Operating system decrements counter
When counter zero generate an interrupt
Set up before scheduling process to regain control or terminate program
that exceeds allotted time
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ProcessManagement
•  Process=programinexecu+on!
–  Program=passive
–  Process=ac+ve
•  Processneedsresources(CPU,memory,I/O,
ini+aliza+ondata,files,etc.)
•  Single-threadedprocess:oneprogram
counter(PC)
•  Mul5-threadedprocess:oneprogramcounter
perthread
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Process Management Activities
The operating system is responsible for the following
activities in connection with process management:
• 
• 
• 
• 
• 
Creating and deleting both user and system processes
Suspending and resuming processes
Providing mechanisms for process synchronization
Providing mechanisms for process communication
Providing mechanisms for deadlock handling
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Memory Management
•  All data in memory before and after processing
•  All instructions in memory in order to execute
•  Memory management determines what is in memory
and when
–  Optimizing CPU utilization and computer response to
users
•  Memory management activities
–  Keeping track of which parts of memory are currently being
used and by whom
–  Deciding which processes (or parts thereof) and data to
move into and out of memory
–  Allocating and de-allocating memory space as needed
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Storage Management
•  OS provides uniform, logical view of information storage
–  Abstracts physical properties to logical storage unit - file
–  Each medium is controlled by device (i.e., disk drive, tape drive)
•  Varying properties include access speed, capacity, data-transfer rate,
access method (sequential or random)
•  File-System management
–  Files usually organized into directories
–  Access control on most systems to determine who can access
what
–  OS activities include
• 
• 
• 
• 
Creating and deleting files and directories
Primitives to manipulate files and directories
Mapping files onto secondary storage
Backup files onto stable (non-volatile) storage media
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Mass-Storage Management
•  Usually disks used to store data that does not fit in main
memory or data that must be kept for a “long” period of time
•  Proper management is of central importance
•  Entire speed of computer operation hinges on disk subsystem
and its algorithms
•  OS activities
–  Free-space management
–  Storage allocation
–  Disk scheduling
•  Some storage need not be fast
–  Tertiary storage includes optical storage, magnetic tape
–  Still must be managed – by OS or applications
–  Varies between WORM (write-once, read-many-times) and RW
(read-write)
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Performance of Various Levels of Storage
Level
1
2
3
4
5
Name
registers
cache
main memory
solid state disk
magnetic disk
Typical size
< 1 KB
< 16MB
< 64GB
< 1 TB
< 10 TB
Implementation
technology
custom memory on-chip or
off-chip
with multiple
CMOS SRAM
ports CMOS
CMOS SRAM
flash memory
magnetic disk
Access time (ns)
0.25 - 0.5
80 - 250
25,000 - 50,000
5,000,000
Bandwidth (MB/sec)
20,000 - 100,000 5,000 - 10,000
1,000 - 5,000
500
20 - 150
Managed by
compiler
0.5 - 25
hardware
operating system operating system operating system
disk or tape
disk
main memory disk
cache
Backed by
•  Movementbetweenlevelsofstoragehierarchycanbe
explicitorimplicit
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Protection and Security
•  Protection – any mechanism for
controlling access of processes or users to
resources defined by the OS
•  Security – defense of the system against
internal and external attacks
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Recap
•  KeyPoints
–  WhatisDMA?
–  Whatisthememoryhierarchy?
–  Whatiscaching?
–  Whatisvirtualmemory?
–  WhatisaSAN?
–  Whatisthedifferencebetweenkernelanduser
mode?
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