Presentation1 cc

OPERATING
SYSTEMS

Operating System Infosys-Campus Connect M.LAVANYA M.C.A Dept

Objectives
To provide a grand tour of the major operating
systems components
To provide coverage of basic computer system
organization


What is an Operating System?

A program that acts as an intermediary between a user
of a computer and the computer hardware.
Operating system goals:
Use the computer hardware in an efficient manner.


Computer System Structure
Computer system can be divided into four
components
Hardware
Operating system
Application programs
Users


Operating System Definition
OS is a resource allocator
OS is a control program


Computer Startup
bootstrap program is loaded at power-up or reboot
Typically stored in ROM or EPROM, generally known
as firmware
Initializates all aspects of system
Loads operating system kernel and starts execution


Computer System Organization


Migration of Integer A from Disk to Register

Multitasking environments must be careful to use most recent
value, no matter where it is stored in the storage hierarchy

Multiprocessor environment must provide cache coherency in
hardware such that all CPUs have the most recent value in their
cache
Distributed environment situation even more complex
 Several copies of a datum can exist
 Various solutions covered in Chapter 17


Operating System Structure
 Multiprogramming needed for efficiency
 Single user cannot keep CPU and I/O devices busy at all times
 Multiprogramming organizes jobs (code and data) so CPU always
has one to execute
 A subset of total jobs in system is kept in memory
 One job selected and run via job scheduling
 When it has to wait (for I/O for example), OS switches to another
job
 Timesharing (multitasking) is logical extension in which CPU
switches jobs so frequently that users can interact with each job while
it is running, creating interactive computing
 Response time should be < 1 second
 Each user has at least one program executing in memory process
 If several jobs ready to run at the same time  CPU scheduling
 If processes don’t fit in memory, swapping moves them in and
out to run
 Virtual memory allows execution of processes not completely in
memory

Operating-System Operations
Interrupt driven by hardware
Software error or request creates exception or trap
 Division by zero, request for operating system service
Other process problems include infinite loop, processes
modifying each other or the operating system
Dual-mode operation allows OS to protect itself and
other system components
 User mode and kernel mode
 Mode bit provided by hardware
 Provides ability to distinguish when system is running user code or
kernel code
 Some instructions designated as privileged, only executable in
kernel mode
 System call changes mode to kernel, return from call resets it to
user


Transition 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


Process Management
 A process is a program in execution. It is a unit of work within the
system. Program is a passive entity, process is an active entity.
 Process needs resources to accomplish its task
 CPU, memory, I/O, files
 Initialization data
 Process termination requires reclaim of any reusable resources
 Single-threaded process has one program counter specifying
location of next instruction to execute
 Process executes instructions sequentially, one at a time, until
completion
 Multi-threaded process has one program counter per thread
 Typically system has many processes, some user, some operating
system running concurrently on one or more CPUs
 Concurrency by multiplexing the CPUs among the processes /
threads

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


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
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 deallocating memory space as needed

Memory Management
Single Contiguous Memory Allocation
Fixed Partition Memory Allocation
Variable Partition Memory Allocation
Relocatable Partition Memory Allocation
Simple Paged Allocation


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 dirs
 Mapping files onto secondary storage
 Backup files onto stable (non-volatile) storage media


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
 Huge range, including denial-of-service, worms, viruses, identity
theft, theft of service
Systems generally first distinguish among users, to determine
who can do what
 User identities (user IDs, security IDs) include name and
associated number, one per user
 User ID then associated with all files, processes of that user to
determine access control
 Group identifier (group ID) allows set of users to be defined and
controls managed, then also associated with each process, file
 Privilege escalation allows user to change to effective ID with
more rights


Computing Environments
 Traditional computer
 Blurring over time
 Office environment
PCs connected to a network, terminals attached to mainframe or
minicomputers providing batch and timesharing
 Now portals allowing networked and remote systems access to same
resources
 Home networks
 Used to be single system, then modems

 Now firewalled, networked


Client-Server Computing
Dumb terminals supplanted by smart PCs
Many systems now servers, responding to requests generated by
clients
 Compute-server provides an interface to client to request
services (i.e. database)
 File-server provides interface for clients to store and retrieve
files


Peer-to-Peer Computing
Another model of distributed system
P2P does not distinguish clients and servers
Instead all nodes are considered peers
May each act as client, server or both
Node must join P2P network
 Registers its service with central lookup service on network,
or
 Broadcast request for service and respond to requests for
service via discovery protocol
Examples include Napster and Gnutella


Several jobs are kept in main memory at the same time, and the
CPU is multiplexed among them.


OS Features Needed for Multiprogramming

I/O routine supplied by the system.
Memory management – the system must
allocate the memory to several jobs.
CPU scheduling – the system must choose
among several jobs ready to run.
Allocation of devices.


Distributed Systems
Distribute the computation among several
physical processors.
Loosely coupled system – each processor has its
own local memory; processors communicate with
one another through various communications
lines, such as high-speed buses or telephone
lines.
Advantages of distributed systems.
 Resources Sharing
 Computation speed up – load sharing
 Reliability
 Communications


Time-Sharing Systems–Interactive Computing

The CPU is multiplexed among several jobs that
are kept in memory and on disk (the CPU is
allocated to a job only if the job is in memory).
A job swapped in and out of memory to the disk.
On-line communication between the user and
the system is provided; when the operating
system finishes the execution of one command, it
seeks the next “control statement” from the user’s
keyboard.
On-line system must be available for users to
access data and code.


Real-Time Systems
Often used as a control device in a dedicated
application such as controlling scientific
experiments, medical imaging systems,
industrial control systems, and some display
systems.
Well-defined fixed-time constraints.
Real-Time systems may be either hard or soft
real-time.


Real-Time Systems (Cont.)
Hard real-time:
 Secondary storage limited or absent, data stored in
short term memory, or read-only memory (ROM)
 Conflicts with time-sharing systems, not supported
by general-purpose operating systems.

Soft real-time
 Limited utility in industrial control of robotics
 Useful in applications (multimedia, virtual reality)
requiring advanced operating-system features.


Processes
Process Concept
Process Scheduling
Operations on Processes
Cooperating Processes
Interprocess Communication
Communication in Client-Server Systems


Process Concept
An operating system executes a variety of
programs:
 Batch system – jobs
 Time-shared systems – user programs or tasks
Process – a program in execution;
process execution must progress in sequential
fashion.
A process includes:
 program counter
 stack
 data section


Process State
As a process executes, it changes state
 new: The process is being created.
 running: Instructions are being executed.
 waiting: The process is waiting for some event to
occur.
 ready: The process is waiting to be assigned to a
process.
 terminated: The process has finished execution.


Process Creation


Process Termination


Processes
Not-running
ready to execute
Blocked
waiting for I/O
Dispatcher cannot just select the process that has
been in the queue the longest because it may be
blocked


A Five-State Model
Running
Ready
Blocked
New
Exit


Suspended Processes
Processor is faster than I/O so all processes could be
waiting for I/O
Swap these processes to disk to free up more memory
Blocked state becomes suspend state when swapped
to disk
Two new states
Blocked/Suspend
ReadySuspend


One Suspend State

Case study -Two Suspend State

Two Suspend States


Process Control Block (PCB)
Information associated with each process.
Process state
Program counter
CPU registers
CPU scheduling information
Memory-management information
Accounting information
I/O status information


Process Scheduling Queues
Job queue – set of all processes in the system.
Ready queue – set of all processes residing in main
memory, ready and waiting to execute.
Device queues – set of processes waiting for an I/O
device.
Process migration between the various queues.


Implementation Questions
How are links established?
Can a link be associated with more than two
processes?
How many links can there be between every pair of
communicating processes?
What is the capacity of a link?
Is the size of a message that the link can
accommodate fixed or variable?
Is a link unidirectional or bi-directional?


Direct Communication
Processes must name each other explicitly:
send (P, message) – send a message to process P
receive(Q, message) – receive a message from process
Q
Properties of communication link
Links are established automatically.
A link is associated with exactly one pair of
communicating processes.
Between each pair there exists exactly one link.
The link may be unidirectional, but is usually bi-
directional.

Indirect Communication
Messages are directed and received from
mailboxes (also referred to as ports).
 Each mailbox has a unique id.
 Processes can communicate only if they share a
mailbox.
Properties of communication link
 Link established only if processes share a common
mailbox
 A link may be associated with many processes.
 Each pair of processes may share several
communication links.
 Link may be unidirectional or bi-directional.


Operations
create a new mailbox
send and receive messages through mailbox
destroy a mailbox
Primitives are defined as:
send(A, message) – send a message to mailbox
A
receive(A, message) – receive a message from
mailbox A


Mailbox sharing
P1, P2, and P3 share mailbox A.
P1, sends; P2 and P3 receive.
Who gets the message?
Solutions
Allow a link to be associated with at most two
processes.
Allow only one process at a time to execute a receive
operation.
Allow the system to select arbitrarily the receiver.
Sender is notified who the receiver was. Dept
Operating System Infosys-Campus Connect M.LAVANYA M.C.A

CPU Scheduling
Basic Concepts
Scheduling Criteria
Scheduling Algorithms
Multiple-Processor Scheduling
Real-Time Scheduling
Algorithm Evaluation


Basic Concepts
Maximum CPU utilization obtained with
multiprogramming
CPU–I/O Burst Cycle – Process execution consists of
a cycle of CPU execution and I/O wait.
CPU burst distribution


CPU Scheduler
Selects from among the processes in memory that are
ready to execute, and allocates the CPU to one of them.
CPU scheduling decisions may take place when a process:
1. Switches from running to waiting state.
2. Switches from running to ready state.
3. Switches from waiting to ready.
4.Terminates.
Scheduling under 1 and 4 is nonpreemptive.
All other scheduling is preemptive.


Dispatcher
Dispatcher module gives control of the CPU to the
process selected by the short-term scheduler; this
involves:
switching context
switching to user mode
jumping to the proper location in the user program to
restart that program
Dispatch latency – time it takes for the dispatcher to
stop one process and start another running.


Scheduling Criteria
CPU utilization – keep the CPU as busy as
possible
Throughput – # of processes that complete their
execution per time unit
Turnaround time – amount of time to execute a
particular process
Waiting time – amount of time a process has
been waiting in the ready queue
Response time – amount of time it takes from
when a request was submitted until the first
response is produced, not output (for time-
sharing environment)

Optimization Criteria

Optimization Criteria
Max CPU utilization
Max throughput
Min turnaround time
Min waiting time
Min response time


First-Come , First-Served (FCFS) Scheduling
Process Burst Time
P1 24
P2 3
P3 3
Suppose that the processes arrive in the order: P1 , P2 , P3
The Gantt Chart for the schedule is:
P1 P2 P3

0 24 27 30

Waiting time for P1 = 0; P2 = 24; P3 = 27
Average waiting time: (0 + 24 + 27)/3 = 17


FCFS Scheduling (Cont.)
Suppose that the processes arrive in the order
P2 , P3 , P1 .
The Gantt chart for the schedule is:

P2 P3 P1

0 3 6 30

Waiting time for P1 = 6; P2 = 0; P3 = 3
Average waiting time: (6 + 0 + 3)/3 = 3
Much better than previous case.
Convoy effect short process behind long process

Shortest-Job-First (SJR) Scheduling
Associate with each process the length of its next CPU
burst. Use these lengths to schedule the process with the
shortest time.
Two schemes:
 nonpreemptive – once CPU given to the process it cannot be
preempted until completes its CPU burst.
 preemptive – if a new process arrives with CPU burst length
less than remaining time of current executing process,
preempt. This scheme is know as the
Shortest-Remaining-Time-First (SRTF).
SJF is optimal – gives minimum average waiting time for a
given set of processes.


Example of Non-Preemptive SJF
Process Arrival Time Burst Time
P1 0.0 7
P2 2.0 4
P3 4.0 1
P4 5.0 4
SJF (non-preemptive)
P1 P3 P2 P4

0 3 7 8 12 16

Average waiting time = (0 + 6 + 3 + 7)/4 - 4


Example of Preemptive SJF
Process Arrival Time Burst Time
P1 0.0 7
P2 2.0 4
P3 4.0 1
P4 5.0 4
SJF (preemptive)
P1 P2 P3 P2 P4 P1

0 2 4 5 7 11 16

Average waiting time = (9 + 1 + 0 +2)/4 - 3


Operating System Infosys-Campus Connect
M.LAVANYA M.C.A Dept

Determining Length of Next CPU Burst
Can only estimate the length.
Can be done by using the length of previous CPU
bursts, using exponential averaging.
1. tn = actual lenght of nthCPU burst
2. τ n +1 = predicted value for the next CPU burst
3. α , 0 ≤ α ≤ 1
4. Define :

τ n=1 = α tn + (1 − α )τ n .


Priority Scheduling
A priority number (integer) is associated with each
process
The CPU is allocated to the process with the highest
priority (smallest integer ≡ highest priority).
 Preemptive
 nonpreemptive
SJF is a priority scheduling where priority is the predicted
next CPU burst time.
Problem ≡ Starvation – low priority processes may never
execute.
Solution ≡ Aging – as time progresses increase the priority
of the process.

Round Robin (RR)
Each process gets a small unit of CPU time (time
quantum), usually 10-100 milliseconds. After this time has
elapsed, the process is preempted and added to the end of
the ready queue.
If there are n processes in the ready queue and the time
quantum is q, then each process gets 1/n of the CPU time
in chunks of at most q time units at once. No process
waits more than (n-1)q time units.
Performance
 q large ⇒ FIFO
 q small ⇒ q must be large with respect to context switch,
otherwise overhead is too high.


Example of RR with Time Quantum = 20
Process Burst Time
P1 53
P2 17
P3 68
P4 24
 The Gantt chart is:

P1 P2 P3 P4 P1 P3 P4 P1 P3 P3

0 20 37 57 77 97 117 121 134 154 162

 Typically, higher average turnaround than SJF, but better
response.


Traditional UNIX Scheduling
Multilevel feedback using round robin within each of
the priority queues
If a running process does not block or complete
within 1 second, it is preempted
Priorities are recomputed once per second
Base priority divides all processes into fixed bands of
priority levels


Memory Management
Background
Swapping
Contiguous Memory Allocation
Paging
Structure of the Page Table
Segmentation
Example: The Intel Pentium


Objectives
To provide a detailed description of
various ways of organizing memory
hardware
To discuss various memory-management
techniques, including paging and
segmentation
To provide a detailed description of the
Intel Pentium, which supports both pure
segmentation and segmentation with
paging


Background
Program must be brought (from disk) into
memory and placed within a process for it to be
run
Main memory and registers are only storage
CPU can access directly
Register access in one CPU clock (or less)
Main memory can take many cycles
Cache sits between main memory and CPU
registers
Protection of memory required to ensure
correct operation


Base and Limit Registers
A pair of base and limit registers define the
logical address space


Binding of Instructions and Data to Memory
Address binding of instructions and data to memory
addresses can happen at three different stages
 Compile time: If memory location known a priori,
absolute code can be generated; must recompile code
if starting location changes
 Load time: Must generate relocatable code if
memory location is not known at compile time
 Execution time: Binding delayed until run time if the
process can be moved during its execution from one
memory segment to another. Need hardware support
for address maps (e.g., base and limit registers)


Logical vs. Physical Address Space
The concept of a logical address space that is
bound to a separate physical address space is
central to proper memory management
 Logical address – generated by the CPU; also
referred to as virtual address
 Physical address – address seen by the memory
unit
Logical and physical addresses are the same in
compile-time and load-time address-binding
schemes; logical (virtual) and physical addresses
differ in execution-time address-binding scheme


Memory-Management Unit (MMU)
Hardware device that maps virtual to physical
address

In MMU scheme, the value in the relocation
register is added to every address generated by
a user process at the time it is sent to memory

The user program deals with logical addresses;
it never sees the real physical addresses


Dynamic Loading
Routine is not loaded until it is called
Better memory-space utilization; unused
routine is never loaded
Useful when large amounts of code are needed
to handle infrequently occurring cases
No special support from the operating system is
required implemented through program design


Dynamic Linking
Linking postponed until execution time
Small piece of code, stub, used to locate the
appropriate memory-resident library routine
Stub replaces itself with the address of the
routine, and executes the routine
Operating system needed to check if routine is
in processes’ memory address
Dynamic linking is particularly useful for
libraries
System also known as shared libraries


Swapping
 A process can be swapped temporarily out of memory to a backing store, and
then brought back into memory for continued execution

 Backing store – fast disk large enough to accommodate copies of all memory
images for all users; must provide direct access to these memory images

 Roll out, roll in – swapping variant used for priority-based scheduling
algorithms; lower-priority process is swapped out so higher-priority process
can be loaded and executed

 Major part of swap time is transfer time; total transfer time is directly
proportional to the amount of memory swapped

 Modified versions of swapping are found on many systems (i.e., UNIX, Linux,
and Windows)
 System maintains a ready queue of ready-to-run processes which have
memory images on disk


Schematic View of Swapping


Contiguous Allocation (Cont.)
 Multiple-partition allocation
 Hole – block of available memory; holes of various
size are scattered throughout memory
 When a process arrives, it is allocated memory from a
hole large enough to accommodate it
 Operating system maintains information about:
a) allocated partitions b) free partitions (hole)

OS OS OS OS

process 5 process 5 process 5 process 5
process 9 process 9

process 8 process 10

process 2 process 2 process 2 process 2

Operating System Infosys-Campus Connect M.LAVANYA M.C.A
Dept

Dynamic Storage-Allocation Problem
How to satisfy a request of size n from a list of free holes
First-fit: Allocate the first hole that is big enough
Best-fit: Allocate the smallest hole that is big
enough; must search entire list, unless ordered by
size
 Produces the smallest leftover hole
Worst-fit: Allocate the largest hole; must also
search entire list
 Produces the largest leftover hole

First-fit and best-fit better than worst-fit in terms of
speed and storage utilization


Paging
 Logical address space of a process can be noncontiguous;
process is allocated physical memory whenever the latter
is available
 Divide physical memory into fixed-sized blocks called
frames (size is power of 2, between 512 bytes and 8,192
bytes)
 Divide logical memory into blocks of same size called
pages
 Keep track of all free frames
 To run a program of size n pages, need to find n free
frames and load program
 Set up a page table to translate logical to physical
addresses
 Internal fragmentation


Address Translation Scheme
 Address generated by CPU is divided into:

 Page number (p) – used as an index into a page table which
contains base address of each page in physical memory

 Page offset (d) – combined with base address to define the
physical memory address that is sent to the memory unit

page number page offset
p d
m-n n
 For given logical address space 2m and page size 2n


Operating System Infosys-Campus
Connect M.LAVANYA M.C.A
Dept

32-byte memory and 4-byte pages

Before allocation After allocation

Implementation of Page Table
 Page table is kept in main memory
 Page-table base register (PTBR) points to the page
table
 Page-table length register (PRLR) indicates size of
the page table
 In this scheme every data/instruction access requires
two memory accesses. One for the page table and one
for the data/instruction.
 The two memory access problem can be solved by the
use of a special fast-lookup hardware cache called
associative memory or translation look-aside
buffers (TLBs)
 Some TLBs store address-space identifiers (ASIDs) in
each TLB entry – uniquely identifies each process to
provide address-space protection for that process


Associative Memory
Associative memory – parallel search
Page # Frame #

Address translation (p, d)
If p is in associative register, get frame # out
Otherwise get frame # from page table in
memory


Effective Access Time
Associative Lookup = ε time unit
Assume memory cycle time is 1 microsecond
Hit ratio – percentage of times that a page
number is found in the associative registers;
ratio related to number of associative registers
Hit ratio = α
Effective Access Time (EAT)
EAT = (1 + ε) α + (2 + ε)(1 – α)
=2+ε–α
CASE STUDY-UNIX and Solaris
Memory Management

UNIX and Solaris Memory Management
Page Replacement
Refinement of the clock policy


Memory Protection
Memory protection implemented by
associating protection bit with each frame

Valid-invalid bit attached to each entry in
the page table:
“valid” indicates that the associated page is in
the process’ logical address space, and is thus
a legal page
“invalid” indicates that the page is not in the
process’ logical address space


Shared Pages
Shared code
One copy of read-only (reentrant) code
shared among processes (i.e., text editors,
compilers, window systems).
Shared code must appear in same location in
the logical address space of all processes

Private code and data
Each process keeps a separate copy of the
code and data
The pages for the private code and data can
appear anywhere in the logical address space


Segmentation scheme that supports user
Memory-management
view of memory
A program is a collection of segments. A segment is
a logical unit such as:
main program,
procedure,
function,
method,
object,
local variables, global variables,
common block,
stack,
symbol table, arrays


1

4
1

2

3 2
4

3

user space physical memory space

Operating System Infosys-Campus Connect M.LAVANYA
M.C.A Dept

Segmentation Architecture
Logical address consists of a two tuple:
<segment-number, offset>,
Segment table – maps two-dimensional
physical addresses; each table entry has:
 base – contains the starting physical address
where the segments reside in memory
 limit – specifies the length of the segment
Segment-table base register (STBR) points
to the segment table’s location in memory
Segment-table length register (STLR)
indicates number of segments used by a
program;
segment number s is legal if s <
STLR
Dept

Segmentation Architecture (Cont.)
Protection
With each entry in segment table associate:
 validation bit = 0 ⇒ illegal segment
 read/write/execute privileges

Protection bits associated with segments;
code sharing occurs at segment level
Since segments vary in length, memory
allocation is a dynamic storage-allocation
problem
A segmentation example is shown in the
following diagram
Dept

Example: The Intel Pentium
Supports both segmentation and segmentation with
paging
CPU generates logical address
Given to segmentation unit
 Which produces linear addresses
Linear address given to paging unit
 Which generates physical address in main memory
 Paging units form equivalent of MMU

Dept

Background
Virtual memory – separation of user logical
memory from physical memory.
Only part of the program needs to be in memory
for execution.
Logical address space can therefore be much
larger than physical address space.
Allows address spaces to be shared by several
processes.
Allows for more efficient process creation.

Virtual memory can be implemented via:
Demand paging
Demand segmentation
Connect
Dept
M.LAVANYA M.C.A

⇒

Dept

Demand Paging
Bring a page into memory only when it is needed
Less I/O needed
Less memory needed
Faster response
More users

Page is needed ⇒ reference to it
invalid reference ⇒ abort
not-in-memory ⇒ bring to memory

Dept

Performance of Demand Paging
Page Fault Rate 0 ≤ p ≤ 1.0
if p = 0 no page faults
if p = 1, every reference is a fault

Effective Access Time (EAT)
EAT = (1 – p) x memory access
+ p (page fault overhead
+ [swap page out ]
+ swap page in
Connect
+ restart overhead)
M.LAVANYA M.C.A
Dept

Copy-on-Write
Copy-on-Write (COW) allows both parent and child
processes to initially share the same pages in memory

If either process modifies a shared page, only then is
the page copied

COW allows more efficient process creation as only
modified pages are copied

Free pages are allocated from a pool of zeroed-out
pages Connect
Dept
M.LAVANYA M.C.A

Page Replacement
Prevent over-allocation of memory by modifying
page-fault service routine to include page
replacement

Use modify (dirty) bit to reduce overhead of page
transfers – only modified pages are written to disk

Page replacement completes separation between
logical memory and physical memory – large virtual
memory can be provided on a smaller physical
memory Operating System
Connect
Infosys-Campus
M.LAVANYA M.C.A
Dept

Basic Page Replacement
1. Find the location of the desired page on disk

2. Find a free frame:
- If there is a free frame, use it
- If there is no free frame, use a page
replacement algorithm to select a victim
frame

3. Read the desired page into the (newly) free
frame. Update the page and frame tables.

4. Restart the process
Operating System
Connect
Infosys-Campus
M.LAVANYA M.C.A
Dept

NTFS(New Technology File System
Features of NTFS
Security and access control
Size of the files/The number of Files
Recovery/Reliability
Long file names

Dept

NTFS(New Technology File System
Overview of the partition structure
Limitations of NTFS

Dept

Device Management
I/O Channels
I/O devices and the CPU can execute concurrently.
Each device controller is in charge of a particular device
type.
Each device controller has a local buffer.
CPU moves data from/to main memory to/from local
buffers
I/O is from the device to local buffer of controller.
Device controller informs CPU that it has finished its
operation by causing an interrupt.
Dept

Common Functions of Interrupts
Interrupt transfers control to the interrupt service
routine generally, through the interrupt vector .
Incoming interrupts are disabled while another
interrupt is being processed to prevent a lost
interrupt.
A trap is a software-generated interrupt caused
either by an error or a user request.
An operating system is interrupt driven.

Dept

Interrupt Handling
The operating system preserves the state of the CPU
by storing registers and the program counter.
Determines which type of interrupt has occurred:
polling
vectored interrupt system
Separate segments of code determine what action
should be taken for each type of interrupt

Dept

I/O Structure
After I/O starts, control returns to user program only
upon I/O completion.
 Wait instruction idles the CPU until the next interrupt
 Wait loop (contention for memory access).
 At most one I/O request is outstanding at a time, no
simultaneous I/O processing.
After I/O starts, control returns to user program
without waiting for I/O completion.
 System call – request to the operating system to allow
user to wait for I/O completion.
 Device-status table contains entry for each I/O device
indicating its type, address, and state.
 Operating system indexes into I/O device table to
determine device status and to modify table entry to
include interrupt.

Dept

Synchronous Asynchronous

Dept

Device Management
User Program e.g. printf(“hello”)
language I/O interface
Run-time Library
System Call interface:
… write stream of
chars
Identify device,
I/O Manager check permissions
Operating
System
Device Driver
Hardware interface:
…write character
Interface Hardware
… put bits on screen
… write disk block
Dept

Device Speeds
Device Transfer Rate CPU Instructions per
(bytes per second)byte transferred (*)
Keyboard 10 10 million

56K modem
6.8 K ~15 thousand

Ethernet 1M+ 100
(Cable modem? (~63K) (~1500)
ADSL?)
Disk Drive 10 M ~10
(CD ROM?) (few M) (tens)
Screen
10s M ~2
(Printer?)
(*) assume 100 MIPS.
CPU speed: instructions/second (cf with clock speed: MHz)
E.g.: Pentium 1GHz: up to 3000 MIPS, but, ...

Dept

I/O Hardware
Variety of devices (WO, RO, RW)
Communicate with the machine via a
connection point: port (e.g., serial port)
Devices within a computer are connected
via a bus.
Controller: electronics that can operate a
port, a bus, or a device.
SCSI bus controller - host adapter circuit board:
processes SCSI protocol messages

Dept

An Input/Output interface
Input Buffer
Memory

Output Buffer

Control

input ready
CPU Status

output ready
Bus

Dept

Synchronising CPU and I/O
Polling:
CPU loops waiting for I/O ready
simple, reliable
slow if many quiescent devices
wastes CPU time
not good for time-critical systems

Interrupts:
CPU initiates I/O action
CPU does other stuff
I/O interface signals ready by interrupting CPU
needs hardware support

Dept

Interrupt Actions (Bacon, figs 3.4, 3.5)
Interrupt
Program Service
Routine

Memory
ISR

Program Vector CPU
Table
PC
PSR

Dept

Interrupt Priorities
Some events:
routine
urgent
 should interrupt routine events
critical
 should interrupt urgent and routine events


Priorities in action
Medium
Priority
Low Priority High
Program ISR
ISR
Priority
ISR

Issues:
High Priority • how should we hold PC/PSR/etc?
ISR • low priority interrupts during
high priority ISR’s
Program
Low Priority
ISR

Dept

Assigning Interrupt Priorities
High Priorities
What type of devices?

Lower Priorities
What type of devices?

Dept

File System Management
MS-DOS File System
File –Organization in MS-DOS
Data Access in MS-DOSn
Volume Structure of the Disk in MS-DOS
MS-DOS Booting Process
UNIX File System

Dept

The UNIX Filesystem
· The UNIX filesystem and directory structure.
· File and directory handling commands.
· How to make symbolic and hard links.
· How wildcard filename expansion works.
· What argument quoting is and when it should be
used.

Dept

The UNIX Filesystem
UNIX filesystem belongs to one of four types:
Ordinary files
Directories
Devices
Links

Dept

Typical UNIX Directory Structure

Dept

Specifying multiple filenames
'?' matches any single character in that position in the
filename.
'*' matches zero or more characters in the filename
('[' and ']') will match any filename that has one of
those characters in that position.
A list of comma separated strings enclosed in curly
braces ("{" and "}") will be expanded as a Cartesian
product with the surrounding characters.

Dept

Quotes
Try insert a '' in front of the special character.
Use double quotes (") around arguments to prevent
most expansions.
Use single forward quotes (') around arguments to
prevent all expansions.

Dept

Directory and File Handling Commands
 $ pwd
/usr/bin
implies that /usr/bin is the current working directory.

ls (list directory)
$ ls
bin dev home mnt share usr var
boot etc lib proc sbin tmp vol
 $ ls –a
$ ls -a -l
(or, equivalently,) Connect
Operating System Infosys-Campus M.LAVANYA M.C.A Dept

File Premissions

Dept

Basic Commands in UNIX
$ man ls
$ info ls
$ cd path
$ cd
$ cd –
$ mkdir directory
$ rmdir directory
$ cp source-file(s) destination
$ cp -rd source-directories destination-directory
Dept

Basic Commands in UNIX
$ mv source destination
$ rm target-file(s)
$ rm -rf / home/will
$ cat target-file(s)
$ more target-file(s)

Dept

Direct Memory Access Structure
Used for high-speed I/O devices able to transmit
information at close to memory speeds.
Device controller transfers blocks of data from buffer
storage directly to main memory without CPU
intervention.
Only one interrupt is generated per block, rather than
the one interrupt per byte.

Dept

Storage Structure
Main memory – only large storage media that the
CPU can access directly(RAM)-DRAM:LOAD &SORE.
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 is logically divided into tracks, which are
subdivided into sectors.
The disk controller determines the logical interaction
between the device and the computer.
Dept

PARTS OF MAGNETIC DISK
SPINDLE
TRACK
SECTOR
CYLINDER
PLATTER
ARM

Dept

Storage Hierarchy
Storage systems organized in hierarchy.
Speed
Cost
Volatility
Caching – copying information into faster storage
system; main memory can be viewed as a last cache
for secondary storage.

Dept

Caching
Important principle, performed at many levels in a
computer (in hardware, operating system, software)
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
Dept

Performance of Various Levels of Storage

Movement between levels of storage hierarchy can be
explicit or implicit

Dept

Subject of Comparison NTFS FAT16 FAT32
Operating system A computer running File access is available to File access is available only
compatibility Windows Vista, Windows computers running to computers running
Server 2003, Windows 2000, Microsoft® MS-DOS®, all Microsoft® Windows 95
or Windows XP can access versions of Windows, OSR2, Windows 98,
files on an NTFS partition. A Windows NT, Windows XP, Windows Me,
computer running Windows Vista, and OS/2. Windows 2000,
Windows NT 4.0 with Windows XP, and
Service Pack 4 or later can Windows Vista.
access files on the partition,
but some NTFS features,
such as Disk Quotas, are not
available. Other operating
systems allow no access.

Volume size Recommended minimum Volumes up to 4 GB. Volumes from 512 MB to
volume size is Cannot be used on floppy 2 terabytes.
approximately 10 MB. disks. In Windows Vista, you can
Recommended practical format a FAT32 volume only
maximum for volumes is up to 32 GB.
2 terabytes. Much larger Cannot be used on floppy
sizes are possible. disks.
Cannot be used on floppy
disks.
File size Maximum file size Maximum file size 4 GB Maximum file size 4 GB
16 terabytes minus 64 KB
(244 minus 64 KB)
Files per volume 4,294,967,295 (232 minus 1 65,536 (216 files)
Operating System Infosys-Campus Approximately 4,177,920
files)
Dept

FAT FAT32 (vFAT) NTFS

Systems DOS, Windows9x, all NTs Windows98, NT5 NT4, NT5

Maximal volume size 2 GBytes near by unlimited near by unlimited

Maximal files count around 65000 near by unlimited near by unlimited
Long names (up to 255 Long names (up to 255
Long names (up to 255
File name chars), system character chars), unicode character
chars), system character set.
set. set.
File attributes Basic set Basic set All that programmers want
yes (capability of physical
Security No no encryption, starting from
NT5.0)
Compression no no yes
Fault tolerance middle low fully (automatic)
improved (small
Economy minimal maximal
clusters)
as for FAT, but also
very effective for all
Performance high for small files count additional penalty for
volumes
Operating System big volumes
Infosys-Campus
Dept

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