Presentation1 cc

OPERATING SYSTEMS

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

ObjectivesTo provide a grand tour of the major

operating systems componentsTo 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 StructureComputer system can be divided into

four componentsHardware Operating systemApplication programs Users



Operating System DefinitionOS is a resource allocatorOS is a control program


Computer Startupbootstrap program is loaded at power-up or

rebootTypically stored in ROM or EPROM, generally

known as firmwareInitializates all aspects of systemLoads 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 complexSeveral copies of a datum can existVarious 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 OperationsInterrupt driven by hardwareSoftware error or request creates exception or trap

Division by zero, request for operating system serviceOther process problems include infinite loop,

processes modifying each other or the operating system

Dual-mode operation allows OS to protect itself and other system componentsUser 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 ModeTimer to prevent infinite loop / process

hogging resourcesSet interrupt after specific periodOperating system decrements counterWhen counter zero generate an interruptSet up before scheduling process to regain

control or terminate program that exceeds allotted time


Process ManagementA 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 taskCPU, memory, I/O, files Initialization data

Process termination requires reclaim of any reusable resourcesSingle-threaded process has one program counter specifying

location of next instruction to executeProcess executes instructions sequentially, one at a time,

until completionMulti-threaded process has one program counter per threadTypically system has many processes, some user, some

operating system running concurrently on one or more CPUsConcurrency by multiplexing the CPUs among the processes

/ threads


Process Management ActivitiesThe operating system is responsible for the following

activities in connection with process management:Creating and deleting both user and system

processesSuspending and resuming processesProviding mechanisms for process synchronizationProviding mechanisms for process communicationProviding mechanisms for deadlock handling


Memory ManagementAll data in memory before and after processingAll instructions in memory in order to executeMemory management determines what is in memory

whenOptimizing CPU utilization and computer response to

usersMemory 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 ManagementSingle Contiguous Memory AllocationFixed Partition Memory AllocationVariable Partition Memory AllocationRelocatable Partition Memory AllocationSimple Paged Allocation


Storage ManagementOS provides uniform, logical view of information

storageAbstracts physical properties to logical storage unit -

fileEach 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 directoriesAccess control on most systems to determine who can

access whatOS 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 SecurityProtection – any mechanism for controlling access of

processes or users to resources defined by the OSSecurity – defense of the system against internal and

external attacksHuge range, including denial-of-service, worms, viruses,

identity theft, theft of serviceSystems generally first distinguish among users, to

determine who can do whatUser identities (user IDs, security IDs) include name

and associated number, one per userUser ID then associated with all files, processes of that

user to determine access controlGroup 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 ComputingAnother model of distributed systemP2P does not distinguish clients and servers

Instead all nodes are considered peersMay each act as client, server or bothNode 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 SystemsDistribute 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 ReliabilityCommunications


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 SystemsOften 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-timeLimited utility in industrial control of roboticsUseful in applications (multimedia, virtual

reality) requiring advanced operating-system features.


ProcessesProcess ConceptProcess SchedulingOperations on ProcessesCooperating ProcessesInterprocess CommunicationCommunication in Client-Server

Systems


Process ConceptAn operating system executes a variety of

programs:Batch system – jobsTime-shared systems – user programs or

tasksProcess – a program in execution; process execution must progress in

sequential fashion.A process includes:

program counter stackdata section


Process StateAs 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


Process Termination


ProcessesNot-running

ready to executeBlocked

waiting for I/ODispatcher cannot just select the process that

has been in the queue the longest because it may be blocked


A Five-State ModelRunningReadyBlockedNewExit



Suspended ProcessesProcessor is faster than I/O so all processes

could be waiting for I/OSwap these processes to disk to free up more

memoryBlocked state becomes suspend state when

swapped to diskTwo new states

Blocked/SuspendReadySuspend


One Suspend State

Case study -Two Suspend StateOperating System Infosys-Campus Connect M.LAVANYA M.C.A Dept

Two Suspend States




Process Control Block (PCB)Information associated with each

process.Process stateProgram counterCPU registersCPU scheduling informationMemory-management informationAccounting informationI/O status information




Process Scheduling QueuesJob 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 QuestionsHow 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 CommunicationProcesses must name each other explicitly:

send (P, message) – send a message to process Preceive(Q, message) – receive a message from

process QProperties 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 CommunicationMessages 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.


Indirect CommunicationOperations

create a new mailboxsend and receive messages through mailboxdestroy a mailbox

Primitives are defined as:send(A, message) – send a message to mailbox Areceive(A, message) – receive a message from mailbox A


Indirect CommunicationMailbox sharing

P1, P2, and P3 share mailbox A.P1, sends; P2 and P3 receive.Who gets the message?

SolutionsAllow 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.


CPU SchedulingBasic ConceptsScheduling Criteria Scheduling AlgorithmsMultiple-Processor SchedulingReal-Time SchedulingAlgorithm Evaluation


Basic ConceptsMaximum CPU utilization obtained with

multiprogrammingCPU–I/O Burst Cycle – Process execution

consists of a cycle of CPU execution and I/O wait.

CPU burst distribution




CPU SchedulerSelects 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.


DispatcherDispatcher module gives control of the CPU

to the process selected by the short-term scheduler; this involves:switching contextswitching to user modejumping to the proper location in the user

program to restart that programDispatch latency – time it takes for the

dispatcher to stop one process and start another running.


Scheduling CriteriaCPU utilization – keep the CPU as busy as

possibleThroughput – # of processes that

complete their execution per time unitTurnaround time – amount of time to

execute a particular processWaiting time – amount of time a process

has been waiting in the ready queueResponse 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 CriteriaMax CPU utilizationMax throughputMin turnaround time Min waiting time Min response time


First-Come , First-Served (FCFS) SchedulingProcess Burst TimeP1 24 P2 3 P3 3

Suppose that the processes arrive in the order: P1 , P2 , P3 The Gantt Chart for the schedule is:

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

P1 P2 P3

24 27 300


FCFS Scheduling (Cont.)Suppose that the processes arrive in the order

P2 , P3 , P1 .The Gantt chart for the schedule is:

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

P1P3P2

63 300


Shortest-Job-First (SJR) SchedulingAssociate 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.


Process Arrival Time Burst TimeP1 0.0 7 P2 2.0 4 P3 4.0 1 P4 5.0 4

SJF (non-preemptive)

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

Example of Non-Preemptive SJF

P1 P3 P2

73 160

P4

8 12


Example of Preemptive SJFProcess Arrival Time Burst Time

P1 0.0 7 P2 2.0 4 P3 4.0 1 P4 5.0 4

SJF (preemptive)

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

P1 P3P2

42 110

P4

5 7

P2 P1

16



Determining Length of Next CPU BurstCan only estimate the length.Can be done by using the length of previous

CPU bursts, using exponential averaging.

:Define 4.10 , 3.

burst CPU next the for value predicted 2.burst CPU of lenght actual 1.

1n

thn nt

.t nnn 11


Priority SchedulingA priority number (integer) is associated with each

processThe CPU is allocated to the process with the highest

priority (smallest integer highest priority).Preemptivenonpreemptive

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.

Performanceq large FIFOq small q must be large with respect to context

switch, otherwise overhead is too high.


Example of RR with Time Quantum = 20Process Burst Time

P1 53 P2 17 P3 68 P4 24

The Gantt chart is:

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

P1 P2 P3 P4 P1 P3 P4 P1 P3 P3

0 20 37 57 77 97 117 121 134 154 162


Traditional UNIX SchedulingMultilevel feedback using round robin within

each of the priority queuesIf a running process does not block or

complete within 1 second, it is preemptedPriorities are recomputed once per secondBase priority divides all processes into fixed

bands of priority levels


Memory ManagementBackgroundSwapping Contiguous Memory AllocationPagingStructure of the Page TableSegmentationExample: The Intel Pentium


ObjectivesTo 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


BackgroundProgram 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 cyclesCache sits between main memory and

CPU registersProtection of memory required to ensure

correct operation


Base and Limit RegistersA pair of base and limit registers define

the logical address space


Binding of Instructions and Data to MemoryAddress binding of instructions and data to

memory addresses can happen at three different stagesCompile 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 SpaceThe concept of a logical address space that is

bound to a separate physical address space is central to proper memory managementLogical address – generated by the CPU; also

referred to as virtual addressPhysical address – address seen by the

memory unitLogical 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 LoadingRoutine is not loaded until it is calledBetter memory-space utilization; unused

routine is never loadedUseful 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 LinkingLinking postponed until execution timeSmall 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


SwappingA 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

process 5

process 8

process 2

OS

process 5

process 2

OS

process 5

process 2

OS

process 5

process 9

process 2

process 9

process 10


Dynamic Storage-Allocation ProblemFirst-fit: Allocate the first hole that is big

enoughBest-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

How to satisfy a request of size n from a list of free holes

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


PagingLogical 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 framesTo run a program of size n pages, need to find n

free frames and load programSet 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

For given logical address space 2m and page size 2n

page number page offset

p d

m - n n




32-byte memory and 4-byte pagesOperating System Infosys-Campus Connect M.LAVANYA M.C.A Dept

Before allocation After allocation


Implementation of Page TablePage table is kept in main memoryPage-table base register (PTBR) points to

the page tablePage-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 MemoryAssociative memory – parallel search

Address translation (p, d)If p is in associative register, get frame # outOtherwise get frame # from page table in

memory

Page # Frame #



Effective Access TimeAssociative Lookup = time unitAssume memory cycle time is 1 microsecondHit ratio – percentage of times that a page

number is found in the associative registers; ratio related to number of associative registers

Hit ratio = Effective Access Time (EAT)

EAT = (1 + ) + (2 + )(1 – )= 2 + –


CASE STUDY-UNIX and Solaris Memory Management

UNIX and Solaris Memory ManagementPage Replacement

Refinement of the clock policy


Memory ProtectionMemory 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 PagesShared 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 dataThe pages for the private code and data can

appear anywhere in the logical address space



SegmentationMemory-management scheme that supports

user 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

3

2

4

1

4

2

3

user space physical memory space


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 memorylimit – 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


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




Example: The Intel PentiumSupports both segmentation and

segmentation with pagingCPU 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



BackgroundVirtual 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




BackgroundVirtual 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





Demand PagingBring a page into memory only when it is

neededLess I/O neededLess memory needed Faster responseMore users

Page is needed reference to itinvalid reference abortnot-in-memory bring to memory





Performance of Demand PagingPage 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+ restart overhead)


Copy-on-WriteCopy-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


Page ReplacementPrevent 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



Basic Page Replacement1. 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




NTFS(New Technology File SystemFeatures of NTFS

Security and access controlSize of the files/The number of FilesRecovery/ReliabilityLong file names


NTFS(New Technology File SystemOverview of the partition structureLimitations of NTFS


Device ManagementI/O ChannelsI/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 buffersI/O is from the device to local buffer of controller.Device controller informs CPU that it has finished

its operation by causing an interrupt.Operating System Infosys-Campus Connect M.LAVANYA M.C.A 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.Operating System Infosys-Campus Connect M.LAVANYA M.C.A Dept

Interrupt HandlingThe operating system preserves the state of

the CPU by storing registers and the program counter.

Determines which type of interrupt has occurred:pollingvectored interrupt system

Separate segments of code determine what action should be taken for each type of interrupt



I/O StructureAfter I/O starts, control returns to user

program only upon I/O completion.Wait instruction idles the CPU until the next

interruptWait 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.


Synchronous Asynchronous




Device ManagementUser Program

Run-time Library

Operating System

I/O Manager

Device Driver

Interface Hardware

e.g. printf(“hello”)

Identify device,check permissions

language I/O interface

System Call interface:… write stream of chars

Hardware interface:…write character… put bits on screen… write disk block


Device SpeedsDevice Transfer Rate

(bytes per second)CPU Instructions per

byte transferred (*)

Keyboard 10

56K modem

Ethernet(Cable modem?

ADSL?)Disk Drive(CD ROM?) Screen(Printer?)

6.8 K

10 million

~15 thousand

1 M +(~63K)

10 M(few M)

100 (~1500)

~10(tens)

~210s M

(*) assume 100 MIPS.CPU speed: instructions/second (cf with clock speed: MHz) E.g.: Pentium 1GHz: up to 3000 MIPS, but, ...


I/O HardwareVariety 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


An Input/Output interfaceMemory

CPU

Input Buffer

Output Buffer

Control

Status input ready

output ready

Bus


Synchronising CPU and I/OPolling:

CPU loops waiting for I/O readysimple, reliableslow if many quiescent deviceswastes CPU timenot good for time-critical systems

Interrupts:CPU initiates I/O actionCPU does other stuffI/O interface signals ready by interrupting

CPUneeds hardware support


Interrupt Actions (Bacon, figs 3.4, 3.5)

ProgramInterruptServiceRoutine

MemoryISR

Program VectorTable

CPU

PC

PSR


Interrupt PrioritiesSome events:

routineurgent

should interrupt routine eventscritical

should interrupt urgent and routine events


Priorities in action

Program Low PriorityISR

Medium Priority

ISR HighPriority

ISR

Program

High PriorityISR

Low PriorityISR

Issues:• how should we hold PC/PSR/etc?• low priority interrupts during

high priority ISR’s


Assigning Interrupt PrioritiesHigh Priorities

What type of devices?

Lower PrioritiesWhat type of devices?

File System ManagementMS-DOS File SystemFile –Organization in MS-DOSData Access in MS-DOSnVolume Structure of the Disk in MS-DOSMS-DOS Booting ProcessUNIX File System


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.


The UNIX FilesystemUNIX filesystem belongs to one of four types:

Ordinary filesDirectoriesDevicesLinks


Typical UNIX Directory Structure


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.


QuotesTry 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.


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,) $ ls -al


File Premissions


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


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


Direct Memory Access StructureUsed 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.


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

PARTS OF MAGNETIC DISKSPINDLETRACKSECTORCYLINDERPLATTERARM


Storage HierarchyStorage systems organized in hierarchy.

SpeedCostVolatility

Caching – copying information into faster storage system; main memory can be viewed as a last cache for secondary storage.


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

Dept

CachingImportant principle, performed at many levels in a

computer (in hardware, operating system, software)Information in use copied from slower to faster

storage temporarilyFaster storage (cache) checked first to determine if

information is thereIf it is, information used directly from the cache (fast)If not, data copied to cache and used there

Cache smaller than storage being cachedCache management important design problemCache size and replacement policy


Performance of Various Levels of Storage

Movement between levels of storage hierarchy can be explicit or implicit



Subject of Comparison NTFS FAT16 FAT32Operating system compatibility

A computer running Windows Vista, Windows Server 2003, Windows 2000, or Windows XP can access files on an NTFS partition. A computer running Windows NT 4.0 with Service Pack 4 or later can access files on the partition, but some NTFS features, such as Disk Quotas, are not available. Other operating systems allow no access.

File access is available to computers running Microsoft® MS-DOS®, all versions of Windows, Windows NT, Windows XP, Windows Vista, and OS/2.

File access is available only to computers running Microsoft® Windows 95 OSR2, Windows 98, Windows Me, Windows 2000, Windows XP, and Windows Vista.

Volume size Recommended minimum volume size is approximately 10 MB.Recommended practical maximum for volumes is 2 terabytes. Much larger sizes are possible.Cannot be used on floppy disks.

Volumes up to 4 GB.Cannot be used on floppy disks.

Volumes from 512 MB to 2 terabytes. In Windows Vista, you can format a FAT32 volume only up to 32 GB.Cannot be used on floppy disks.

File size Maximum file size 16 terabytes minus 64 KB (244 minus 64 KB)

Maximum file size 4 GB Maximum file size 4 GB

Files per volume 4,294,967,295 (232 minus 1 files)

65,536 (216 files) Approximately 4,177,920


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

File nameLong names (up to 255 chars), system character set.

Long names (up to 255 chars), system character set.

Long names (up to 255 chars), unicode character set.

File attributes Basic set Basic set All that programmers want

Security No noyes (capability of physical encryption, starting from NT5.0)

Compression no no yes

Fault tolerance middle low fully (automatic)

Economy minimalimproved (small clusters)

maximal

Performance high for small files countas for FAT, but also additional penalty for big volumes

very effective for all volumes

Documents

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