Advanced Operating Advanced Operating SystemsSystems

Prof. Muhammad Saeed

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Course Name: Advanced Operating SystemsCourse Structure: 3 + 0 Course Code: CS703

Text Books/Reference Books:1) Modern Operating Systems by A. S. Tanenbaum 3rd Edition2) Distributed Systems: Concepts and Design by Coulouris, Dollimore, and

Kindberg, 3rd Edition. 3) Distributed Operating Systems: Concepts and Design by Paradeep K. Sinha4) Advanced Concepts in Operating Systems by Singhal and Shiviratri

3Computer Science

Def. in nutshellIt manages hardware resources and provides abstract set of resources.

Web Browser

E-mail ReaderVideo Player

User Interface Program

Operating System

Hardware

User Mode

Kernel Mode

What is an Operating System ?What is an Operating System ?

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• Program developmento Editors and debuggers

• Program execution• Access to I/O devices• Controlled access to files• System access

Services Provided by the Operating SystemServices Provided by the Operating System

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• Error detection and response internal and external hardware errors• memory error• device failure

software errors• arithmetic overflow• access forbidden memory locations

operating system cannot grant request of application

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1) Charles Babbage hired Ada Lovelace as world’s first programmer.2) Vacuum Tubes. Electronic Circuits. 1945-553) Transistors.During 1955-65 Batch System was implemented. Punch Cards introduced.

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4) 1965-80, IC’s and Multiprogramming, spooling (Simultaneous Peripheral Operation On Line), introductory timesharing. IBM System 360, PDP series, MULTICS ( Multiplexed Information and Computing Service)

System V and BSD versions of UNIX (UNICS).5) 1980- ,LSI ,Microcomputers.

i) CPM(Control Program for Microcomputers), Kildall wrote for 8080 and Zilog Z80,

ii) IBM PC Bill Gates provided DOS(Disk Operating System)/Basic package for IBM PC.

iii) Engelbert invented GUI at Stanford Research Institute in the 60’s.iv) Steve Jobs used GUI in Apple Macintosh.v) in 1985 Microsoft developed Windows. Windows 95 was a real GUI

based System.vi) UNIX System with X Windows.vii) Network and Distributed Operating Systemsviii) Multiprocessor Operating Systems.ix) Handheld Computer Operating Systems.x) Embedded Operating Systems.xi) Sensor Node Operating Systems.xii) Real-Time Operating Systems.xiii) Smart Card Operating Systems.

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Processor - traditionally controls the operation of the computer and performs the data processing function

Memory - Stores data and programs, typically volatile (aka real or primary memory)

I/O modules - move data between computer and external environment (i.e. disks, network)

System Bus - communication among processors, memory, and I/O modules

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A processor is hardware that executes machine-languageCPU executes the instructions of a programCoprocessor executes special-purpose instructions• Ex., graphics or audio coprocessors

Registers are high-speed memory located on processors• Data must be in registers before a processor can

operate on itInstruction length is the size of a machine-language

instruction• Some processors support multiple instruction

lengths.

Holding Buffer

Execute Unit

Execute Unit

Execute Unit

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Computer time is measured in cyclesOne complete oscillation of an electrical signalProvided by system clock generatorProcessor speeds are measured in GHz (billions of cycles

per second)• Modern desktops execute at hundreds of megahertz or

several GHz

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The memory hierarchy is a scheme for categorizing memoryFastest and most expensive at the top, slowest and least

expensive at the bottom Registers L1 Cache L2 Cache Main Memory

Secondary and tertiary storage (CDs, DVDs and floppy disks)

Main memory is the lowest data referenced directly by processor

Volatile – loses its contents when the system loses power

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Core 1

L1

Core 2

L1

Core 3

L1

Core 4

L1

L 2 Cache

Core 1

L1

Core 2

L1

Core 3

L1

Core 4

L1

L 2 L 2

L 2 L 2

A quad-core chip with shared L2 Cache A quad-core chip with separate L2 Cache

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Use of high-speed memory to hold recently-accessed data.

Requires a cache management policy.Careful selection of the cache size and of a

replacement policy can result in 80 to 99 percent of all accesses being in cache greatly improving performance

Caching introduces another level in storage hierarchy. This requires data that is simultaneously stored in more than one level to be consistent.

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Device port. Serial Port. Parrallel Port USB (Universal Serial Bus)

The computer acts as the host.Up to 127 devices can connect to the host, either directly or by way of USB hubs.Individual USB cables can run as long as 5 meters; with hubs, devices can be up to 30 meters.With USB 2.0,the bus has a maximum data rate of 480 megabits per second . With USB 3.0, data rate is 5 gbits/sec.

While USB 2.0 can only send data in one direction at a time, USB 3.0 can transmit data in both directions simultaneously. USB of 256 GB capacity are available.

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A bus is a collection of tracesTraces are thin electrical connections that

transport information between hardware devices

A port is a bus that connects exactly two devices

An I/O channel is a bus shared by several devices to perform I/O operations• Handle I/O independently of the system’s

main processors

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Starting up a computerInitial program, or bootstrap program, is runStored in ROM or EPROM within the computer hardwareInitializes all aspects of the computer (registers,

controllers, memory etc.)Loads the operating system and executes it

• Locates and loads the OS kernelOnce loaded, the OS waits for an event to occur

• Events usually signaled by an interrupt from either the hardware or software

Hardware sends a signal to the CPU via the system bus Software triggers an interrupt by executing a system call

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Interrupts enable software to respond to signals from hardwareMay be initiated by a running process• Interrupt is called a trap – software generated caused by

error or user request for an OS service• Dividing by zero or referencing protected memory

May be initiated by some event that may or may not be related to the running process• Key is pressed on a keyboard or a mouse is moved

Low overhead Polling is an alternative approach– Processor repeatedly requests the status of each device– Increases in overhead as the complexity of the system increases

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After receiving an interrupt, the processor completes execution of the current instruction, then pauses the current process

The processor will then transfer to a fixed location and executes the service routine for the interrupt

The interrupt handler determines how the system should respond

Interrupt handlers are stored in an array of pointers called the interrupt vectorTo handle the interrupt quickly, a table of pointers is

generally stored in low memory which hold the addresses of the ISR for the various devices

This array, or interrupt vector, of addresses is then indexed by a unique device number to provide the address of the ISR for the interrupting device

After the interrupt handler completes, the interrupted process is restored and execution continues from the address of the interrupted instruction (stored on stack) or the next process is executed

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To start an I/O operation, the CPU loads the appropriate registers within the device controller

The device controller examines the values and determines what action to take (e.g. read, write)

When the transfer is complete, the device controller informs the CPU via an interrupt

The device driver returns control to the OSReturns the data or pointer to the data if a read was doneFor other operations it returns status information

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Synchronous: After I/O starts, control returns to user program only

upon I/O completion.Wait instruction or tight loop (Loop: jmp Loop)

idles the CPU until the next interruptAt most one I/O request is outstanding at a time, no

simultaneous I/O processing. Asynchronous:

After I/O starts, control returns to user program without waiting for I/O completion.

Increased system efficiency by increasing CPU utilization

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.

If the device is busy with a request, the type of request and other parameters are stored in the table entry for that device

A queue will contain a list of all those requests waiting for a device

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• Processor has more than one program to execute• The sequence the programs are executed depend on

their relative priority and whether they are waiting for I/O

• After an interrupt handler completes, control may not return to the program that was executing at the time of the interrupt

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Uniprogramming Multiprogramming

Processor use 22% 43%

Memory use 30% 67%

Disk use 33% 67%

Printer use 33% 67%

Elapsed time 30 min. 15 min.

Throughput rate 6 jobs/hr 12 jobs/hr

Mean response time 18 min. 10 min.

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• Reduce setup time by batching jobs with similar requirements.• Add a card reader, Hire an operator• User is NOT the operator• Automatic job sequencing

Forms a rudimentary OS.• Resident Monitor

Holds initial control, control transfers to job and then back to monitor.

• Problem Need to distinguish job from job and data from program.

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• Programs queued for execution in FIFO order.• Like multiprogramming, but timer device interrupts after a quantum (time

slice). Interrupted program is returned to end of FIFO Next program is taken from head of FIFO

• Control card interpreter replaced by command language interpreter.

• Interactive (action/response) When OS finishes execution of one command, it seeks the next control

statement from user.• File systems Online file system is required for users to access data and code.• Virtual memory

Job is swapped in and out of memory to disk.

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Monolithic SystemsLayered SystemsMicrokernelsClient-Server ModelVirtual MachinesExokernels.

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Monolithic Systems

Entire Operating System as kernel. All individual procedures first compiled then linked

together. No information hiding. One service procedure for each system call. There may be some user mode and kernel mode. loadable I/O device drivers loaded on demand.

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Layered Systems

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Microkernels:

Splitting into well-defined modules Very few instructions in kernel modeA few of microkernel systems are QNX, Symbian,

MINIX 3 etc.Lesser bugs and rare system crash.

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Client-Server Model: Divided into client processes and server processes Communication between client and server generally

done by message passing. Client and server can be on the same computer.. Web operates in this way

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Virtual Machines:

Copy of hardware, kernel/user mode, I/o, interrupts etc.

Can run any operating system coexisting with other operating systems

Any call is trapped in the operating system of the virtual machine.

Virtualization in the web hosting world uses virtual machines to implement virtualization.

CPU must be virtualizable to run previleged instructions.

Type 1 hypervisor run on hardware but type II hypervisor runs on top of host operating system.

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Exokernals: Rather than cloning the machine

partitioning is used, giving users subset of resources.

Exokernal allocates resources to virtual machines.

Remapping is not needed.

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