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Task 01

Task 1.1)

Graphical User Interface (GUI):

GUI is sort form for Graphical User Interface; generally this is a part of computer’s operating system which is

characterized by WIMPs and WYSIWYG.

WIMPs are Windows, Icons, Menus, and Pointing devices (such as a mouse or a trackball).WYSIWYG or What You See is What You Get, refers to the ability to print out exactly what you see on the screen

this made effective desktop publishing possible.

The GUI is based on the principle that pointing in menus to a command you want to computer to do is easie

than having to remember hundreds of key words like in command line operating systems such as MS DOS or

UNIX. The GUI is based on the idea that pointing to something is the most basic human motion, and the mouse

is easier to use than a keyboard.

(Referance: *1)

The GUI replaced the command line interface because cooperating with a computer using a mouse pointer haseveral benefits over typed commands such as: Intuitive, Multitasking, Application Interface, Rich Media, &

Visualizing Concept.

Intuitive: A GUI is natural; a person who never used computer before can perform basic process with a GU

after few minute training. Users simply click the item they want to work together with. Right-click an item to

open a context menu and see the other things you can do with it. A command line interface is more unclear and

needs memorization the commands.

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Gayan Sachith Kumara | Networking with Windows

Multitasking: One of the key advantages is that GUI-based operating systems are designed for do the

multitasking. You can change the size of any window as needed and place windows side-by-side Or Horizontally

or vertically to see and interact with different programs at the same time. Command line operating systems

generally use full-screen applications; although it may be possible to run multiple applications and switch

between them, it is generally not possible to view them simultaneously.

Rich Media: GUI-based operating systems are designed with rich media such as images, videos and music in

mind and these operating systems utilize programming frameworks such as Microsoft DirectX and Adobe Flash

to make rich media applications easier to develop. Though it is possible to play a video or listen to music on a

command line-based operating system but it is more difficult than GUI.

Application Interface: Applications are designed for GUI-based operating systems tend to have simila

interfaces. For example, many Windows applications have bars at the top of the screen with options such as

"File," "Edit," "Tools" and "Help." If you have used these functions in one Windows application, you know how to

use them in another application even if you have never used that application before.

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Visualizing Concepts: Cooperating with the items on a computer involves several intellectual concepts tha

might be difficult for some to understand. GUI-based operating systems give these concepts visua

representations. New users quickly learn that folders contain files and that you can double-click a folder to open

the folder & to what it holds. A file frequently has a specific icon indicating its type; for example, an audio file

might have an icon depicting a music note.

(Referance: *2)

Command Line Interface (CLI):

A command line interface is a user interface to a computer's operating system or an application in which the

user responds to a visual prompt by typing in a command on a specified line, receives a response back from the

system, and then enters another command, and so forth. The MS-DOS Prompt application in a Windows

operating system is an example of the provision of a command line interface.

(Referance: *3)

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CLI vs. GUI

Topic Command line (CLI) GUI

Simplicity Memorization and familiarity needed to

operate with command line interface; new

users have a difficult time navigating and

operating a command line interface.

Though new users may have a difficult time

learning to use the mouse and all GUI

features, but it is much easier when compared

to the command line interface.

Control Users have more control of the system andoperating system in a command line

interface. As an example, users can copy a

file from one location to another in a one-

command line.

Although a GUI proposals quite of control of afile system and operating system, the more

advanced tasks may still need a command line.

Multitasking Many command line environments are

capable of multitasking; but they do not

provide the ability to view multiple things

at one time.

GUI users have windows that enable a user to

view, control, and use multiple things at once

and are much faster to navigate when

compared with a command line.

Speed Command line users only need to use their

keyboards to navigate a command line

interface and often only need to execute afew lines to perform a task.

A GUI may be easier to use because of the

mouse. However, using a mouse and keyboard

to navigate and control your operating systemfor many things is going to be much slower

than someone who is working in a command

line.

Properties A computer that is only using the command

line takes a lot less of the computers

system resources than a GUI.

A GUI requires more system resources

because of each of the elements that need to

be loaded such as icons, fonts, etc. In addition,

video drivers, mouse drivers, and other drivers

that need to be loaded will also take

additional resources.

Scripting A command line interface enables a user to

script a sequence of commands to perform

a task or execute a program.

Although A GUI enables a user to create

shortcuts, tasks, or other similar actions, it

doesn't even come close in comparison to

what is available through a command line.

Remote access When accessing another computer or

networking device over a network, a user

will only be able to manipulate the device

or its files using a command line interface.

Although remote graphical access is possible.

Not all computers and especially not all

network equipment will have this ability.

Diverse After you've learned how to navigate and

use a command line, it's not going to

change as much as a new GUI. Although

new commands may be introduced, the

original commands always remain the

same.

Each GUI has a different design and structure

of how to perform different tasks. Even

different versions of the same GUI, such as

Windows, can have hundreds of different

changes between each version.

Stress The command line allows the user to keep

their hands on the keyboard and rarely

have to move from the keyboard to the

mouse. Moving back and forth between a

keyboard and mouse can cause additional

strain and may help contribute to Carpal

Tunnel.

Although shortcut keys can be learned to help

reduce the amount of times you have move

from the keyboard to the mouse, you will still

be moving much more between the keyboard

and mouse with a GUI.

(Referance: *4)

http://www.computerhope.com/jargon/r/resource.htm

http://www.computerhope.com/jargon/d/driver.htm

http://www.computerhope.com/jargon/c/carpaltu.htm


http://www.computerhope.com/shortcut.htm

http://www.computerhope.com/shortcut.htm



http://www.computerhope.com/jargon/d/driver.htm

http://www.computerhope.com/jargon/r/resource.htm

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Task 1.2)

Windows O/S

Windows is a major graphical interface operating systems developed and sold by ‘Microsoft”.

Microsoft introduced an operating environment call Windows on November 20, 1985 as a “graphical operating

system shell” for “MS-DOS” in reply to the growing interest in graphical user interfaces (GUI). Windows O/S

came to rule the world's personal computer market with over 90% market share, overtaking Mac OS, which hadbeen introduced in 1984.

October 2013, the most recent versions of Windows for personal computers, smartphones, server computers

and embedded devices are respectively Windows 8.1, Windows Phone 8, Windows Server 2012 R2 and

Windows Embedded 8.

(Referance: *5)

Windows O/S Client side issues:

Insecurity

Variability

Customizability

Compatibility

Insecurity: Due to the brand and closed source nature of Microsoft, the programs don’t experience the hearty

scrutiny and testing Linux systems endure at the hands of the open source community. The limited number o

staff to write and edit the source code for vulnerabilities leaves the systems more prone to attack and due to its

popularity, many more viruses are targeted to hit Microsoft programs these viruses have been known to cause

devastating and costly network losses including the destruction or corruption of confidential corporate files

Further utilizing the resources of an entire community, Linux Vulnerabilities are quickly and correctly patched. In

some cases, Microsoft vulnerabilities are only patched after seeing a problem and many provide only a quick fix

and are in need of further attention in the future.

Variability: As the design flaws of Windows are consistently misused, the stability of the operating system is

under constant threat. These problems are not exclusive to virus and worm exploitation but also the way in

which Windows interacts with other technology. Windows is infamous for not working well with third party

vendor products causing slow processing time and system crashes. Also, letting the end useful administrative

control to machine can result in the inadvertent corruption of system data.

Customizability: Windows does not give the access to customize the program depending specific needs of the

user. If a specific program does not contain all the functionality, style, compatibility, or security desired

organization have to purchase additional products to do the job.

Compatibility: wide range of software available for Windows PCs often is not fully compatible with certain

hardware, causing inconvenience, monetary losses, and system lock-up or software crash.

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Server side

Windows Server requires more system resources.

Need a powerful machine to run Windows Server.

Windows Server does not have a good reputation in terms of server stability.

The costs of the applications are usually higher than UNIX.

No, many free applications in Windows Server world.

Additional Hardware Resources: One disadvantage to using Windows Server is that it requires more resources

for the machine to operate properly. Usually purchasing software will also involve upgrading the hardware. Fo

instance, many software products require more internal memory and a faster, more powerful processor. It also

requires several updates and security patches, usually referred to as service packs. Sometimes, after th

installation of these service packs, problems can occur with the operating system, rendering the server unusable

until the problem is resolved.

Support Costs: There are high costs. The administration of Server 2003 involves having trained support staff. The

staff must be well trained to take advantage of the system, which can be costly. There are licensing costs for

using the software that are not only related to the server itself but also to the client workstations.

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Task 1.3)

MS-DOS (Microsoft disk operating system):

Originally developed by Microsoft for IBM, MS-DOS was the standard operating system for IBM-compatible

personal computers. The initial versions of DOS were very simple and resembled another operating system

called CP/M. Subsequent versions have become increasingly sophisticated as they incorporated features o

minicomputer operating systems.

Windows 1.0 – 2.0 (1985-1992):

Introduced in 1985, Microsoft Windows 1.0 was named due to the computing boxes, or "windows" that

represented a fundamental aspect of the operating system. Instead of typing MS-DOS commands, windows 1.0

allowed users to point and click to access the windows.

In 1987 Microsoft released Windows 2.0, which was designed for the designed for the Intel 286 processor. This

version added desktop icons, keyboard shortcuts and improved graphics support.

Windows 3.0 – 3.1 (1990– 1994)

Microsoft released Windows 3.0 in May, 1900 offering better icons, performance and advanced graphics with 16

colors designed for Intel 386 processors. This version is the first release that provides the standard "look and

feel" of Microsoft Windows for many years to come. Windows 3.0 included Program Manager, File Manager and

Print Manager and games (Hearts, Minesweeper and Solitaire). Microsoft released Windows 3.1 in 1992.

Windows 95 (August 1995)

A major release of the Microsoft Windows operating system released in 1995. Windows 95 represents a

significant advance over its precursor, Windows 3.1. In addition to sporting a new user interface, Windows 95

also includes a number of important internal improvements. Perhaps most important, it supports 32-bi

applications, which means that applications written specifically for this operating system should run much

faster.

Although Windows 95 can run older Windows and DOS applications, it has essentially removed DOS as the

underlying platform. This has meant removal of many of the old DOS limitations, such as 640K of main memory

and 8-character filenames. Other important features in this operating system are the ability to automatically

detect and configure installed hardware (plug and play).

Windows 98 (June 1998)

Windows 98 offers support for a number of new technologies, including FAT32, AGP, MMX, USB, DVD, and ACPI

Its most visible feature, though, is the Active Desktop, which integrates the Web browser (Internet Explorer

with the operating system. From the user's point of view, there is no difference between accessing a documenresiding locally on the user's hard disk or on a Web server halfway around the world.

Windows ME - Millennium Edition (September 2000)

The Windows Millennium Edition, called "Windows Me" was an update to the Windows 98 core and included

some features of the Windows 2000 operating system. This version also removed the "boot in DOS" option.

Windows NT 31. - 4.0 (1993-1996)

Windows NT (New Technology) is a 32-bit operating system that supports preemptive multitasking. There are

actually two versions of Windows NT: Windows NT Server, designed to act as a server in networks, and Window

NT Workstation for stand-alone or client workstations.

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Windows 2000 (February 2000)

Often abbreviated as "W2K," Windows 2000 is an operating system for business desktop and laptop systems to

run software applications connect to Internet and intranet sites, and access files, printers, and network

resources. Microsoft released four versions of Windows 2000: Professional (for business desktop and laptop

systems), Server (both a Web server and an office server), Advanced Server (for line-of-business applications

and Datacenter Server (for high-traffic computer networks).

Windows XP (October 2001)

Windows XP was first introduced in 2001. Along with a redesigned look and feel to the user interface, the new

operating system is built on the Windows 2000 kernel, giving the user a more stable and reliable environmen

than previous versions of Windows. Windows XP comes in two versions, Home and Professional. Microsof

focused on mobility for both editions, including plug and play features for connecting to wireless networks. The

operating system also utilizes the 802.11x wireless security standard. Windows XP is one of Microsoft's best

selling products.

Windows Vista (November 2006)

Windows Vista offered advancement in reliability, security, ease of deployment, performance and manageability

over Windows XP. New in this version was capabilities to detect hardware problems before they occur, security

features to protect against the latest generation of threats, faster start-up time and low power consumption of

the new sleep state. In many cases, Windows Vista is noticeably more responsive than Windows XP on identica

hardware. Windows Vista simplifies and centralizes desktop configuration management, reducing the cost o

keeping systems updated.

Windows 7 (October, 2009)

Windows 7 made its official debut to the public on October 22, 2009 as the latest in the 25-year-old line of

Microsoft Windows operating systems and as the successor to Windows Vista (which itself had followed

Windows XP). Windows 7 was released in conjunction with Windows Server 2008 R2, Windows 7's serve

counterpart. Enhancements and new features in Windows 7 include multi-touch support, Internet Explorer 8improved performance and start-up time, Aero Snap, Aero Shake, support for virtual hard disks, a new and

improved Windows Media Center, and improved security.

Windows 8 (Codename, Expected Release 2012)

Windows 8 is a completely redesigned operating system that's been developed from the ground up with

touchscreen use in mind as well as near-instant-on capabilities that enable a Windows 8 PC to load and start up

in a matter of seconds rather than in minutes. Windows 8 will replace the more traditional Microsoft Windows

OS look and feel with a new "Metro" design system interface that first debuted in the Windows Phone 7 mobile

operating system. The Metro user interface primarily consists of a "Start screen" made up of "Live Tiles," which

are links to applications and features that are dynamic and update in real time. Windows 8 supports both x86PCs and ARM processors. Online media sites indicate that this version will be available in 2012, with October and

fall being the most often quoted time frame

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Task 1.4)

Multitasking is the ability of a computer to run more than one program, or task, at the same time. Multitasking

contrasts with single-tasking, where one process must entirely finish before another can begin. MS-DOS is

primarily a single-tasking environment, while Windows 3.1 and Windows NT are both multi-tasking

environments.

On a single-processor multitasking system, multiple processes don't actually run at the same time since there's

only one processor. Instead, the processor switches among the processes that are active at any given time.

Because computers are so fast compared with people, however, it appears to the user as though the computer

is executing all of the tasks at once. Multitasking also allows the computer to make good use of the time it would

otherwise spend waiting for I/O devices and user input--that time can be used for some other task that doesn't

need I/O at the moment.

Multitasking on a multiple-processor system still involves the processors switching between tasks because there

are almost always more tasks to run than there are processors. Note, however, that there can be as many tasks

running simultaneously as there are processors in the system. For the moment, we'll discuss multitasking on a

single-processor system.

Review: Preemptive and Non-Preemptive Multitasking

Within the category of multitasking, there are two major sub-categories: preemptive and non-preemptive (o

cooperative). In non-preemptive multitasking, use of the processor is never taken from a task; rather, a tas

must voluntarily yield control of the processor before any other task can run. Windows 3.1 uses non-preemptive

multitasking for Windows applications.

Programs running under a non-preemptive operating system must be specially written to cooperate in

multitasking by yielding control of the processor at frequent intervals. Programs that do not yield sufficiently

often because non-preemptive systems to stay "locked" in that program until it does yield. An example of failed

non-preemptive multitasking is the inability to do anything else while printing a document in Microsoft Word foWindows 2.0a. This happens because Word does not give up control of the processor often enough while

printing your document. The worst case of a program not yielding is when a program crashes. Sometimes,

programs which crash in Windows 3.1 will crash the whole system simply because no other tasks can run unti

the crashed program yields.

Preemptive multitasking differs from non-preemptive multitasking in that the operating system can take contro

of the processor without the task's cooperation. (A task can also give it up voluntarily, as in non-preemptive

multitasking.) The process of a task having control taken from it is called preemption. Windows NT uses

preemptive multitasking for all processes except 16-bit Windows 3.1 programs. As a result, a Window NT

application cannot take over the processor in the same way that a Windows 3.1 application can.

A preemptive operating system takes control of the processor from a task in two ways:

When a task's time quantum (or time slice) runs out. Any given task is only given control for a set

amount of time before the operating system interrupts it and schedules another task to run.

When a task that has higher priority becomes ready to run. The currently running task loses control o

the processor when a task with higher priority is ready to run regardless of whether it has time left in it

quantum or not.

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Switching Among Tasks

At any given time, a processor (CPU) is executing in a specific context. This context is made up of the contents of

its registers and the memory (including stack, data, and code) that it is addressing. When the processor needs to

switch to a different task, it must save its current context (so it can later restore the context and continue

execution where it left off) and switch to the context of the new task. This process is called context switching .

When Windows NT switches tasks, it saves all of the registers of the task it's leaving and re-loads the registers of

the task to which it's switching. This process also enables the proper address space for the task to which

Windows NT is switching.

Processes and Threads

Preemptive multitasking differs from non-preemptive multitasking in that the operating system can take contro

of the processor without the task's cooperation. (A task can also give it up voluntarily, as in non-preemptive

multitasking.) The process of a task having control taken from it is called preemption. Windows NT uses

preemptive multitasking for all processes except 16-bit Windows 3.1 programs. As a result, a Window NT

application cannot take over the processor in the same way that a Windows 3.1 application can.

A preemptive operating system takes control of the processor from a task in two ways:

When a task's time quantum (or time slice) runs out. Any given task is only given control for a set

amount of time before the operating system interrupts it and schedules another task to run.

When a task that has higher priority becomes ready to run. The currently running task loses control o

the processor when a task with higher priority is ready to run regardless of whether it has time left in it

quantum or not.

Switching Among Tasks

At any given time, a processor (CPU) is executing in a specific context. This context is made up of the contents ofits registers and the memory (including stack, data, and code) that it is addressing. When the processor needs to

switch to a different task, it must save its current context (so it can later restore the context and continue

execution where it left off) and switch to the context of the new task. This process is called context switching .

When Windows NT switches tasks, it saves all of the registers of the task it's leaving and re-loads the registers of

the task to which it's switching. This process also enables the proper address space for the task to which

Windows NT is switching.

Processes and Threads

In addition to being a preemptive multitasking operating system, Windows NT is also multithreaded, meaningthat more than one thread of execution (or thread ) can execute in a single task at once.

A process comprises:

A private memory addresses space in which the process's code and data are stored.

An access token against which Windows NT makes security checks.

System resources such as files and windows (represented as object handles).

At least one threads to execute the code.

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A thread comprises:

A processor state including the current instruction pointer.

A stack for use when running in user mode.

A stack for use when running in kernel mode.

Since processes (not threads) own the access token, system resource handles, and address space, threads do

NOT have their own address spaces nor do they have their own access token or system resource handles

Therefore, all of the threads in a process SHARE the same memory, access token, and system resources

(including quota limits) on a "per-process" rather than a "per-thread" basis. In a multithreaded program, the

programmer is responsible for making sure that the different threads don't interfere with each other by using

these shared resources in a way that conflicts with another thread's use of the same resource. (As you might

suspect, this can get a little tricky.)

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Task 1.5)

Multiprocessing is the use of two or more central processing units (CPUs) within a single computer system. The

term also refers to the ability of a system to support more than one processor and/or the ability to allocate task

between them. There are many differences on this basic theme, and the definition of multiprocessing can vary

with setting, mostly as a function of how CPUs are defined (multiple cores on one die, multiple dies in one

package, multiple packages in one system unit, etc.).

Multiprocessing sometimes refers to the performance of multiple concurrent software processes in a system as

opposed to a single process at any one instant. However, the terms multitasking or multiprogramming are more

appropriate to describe this concept, which is implemented mostly in software, whereas multiprocessing is more

appropriate to describe the use of multiple hardware CPUs. A system can be both multiprocessing and

multiprogramming, only one of the two, or neither of the two of them

Processor symmetry

Instruction and data streams

Processor symmetry: In a multiprocessing system, all CPUs may be equal, or some may be reserved for specia

purposes. A combination of hardware and operating system software design considerations determine thesymmetry (or lack thereof) in a given system. For example, hardware or software considerations may require

that only one particular CPU respond to all hardware interrupts, whereas all other work in the system may be

distributed equally among CPUs; or execution of kernel-mode code may be restricted to only one particular CPU

whereas user-mode code may be executed in any combination of processors. Multiprocessing systems are often

easier to design if such restrictions are imposed, but they tend to be less efficient than systems in which all CPUs

are utilized.

Systems that treat all CPUs equally are called symmetric multiprocessing (SMP) systems. In systems where al

CPUs are not equal, system resources may be divided in a number of ways, including asymmetri

multiprocessing (ASMP), non-uniform memory access (NUMA) multiprocessing, and clustered multiprocessing.

Instruction and data streams: In multiprocessing, the processors can be used to execute a single sequence o

instructions in multiple contexts (single-instruction, multiple-data or SIMD, often used in vector processing)

multiple sequences of instructions in a single context (multiple-instruction, single-data or MISD, used fo

redundancy in fail-safe systems and sometimes applied to describe pipelined processors or hyper-threading), o

multiple sequences of instructions in multiple contexts (multiple-instruction, multiple-data or MIMD).

Processor coupling: Tightly-coupled multiprocessor systems contain multiple CPUs that are connected at the

bus level. These CPUs may have access to a central shared memory (SMP or UMA), or may participate in a

memory hierarchy with both local and shared memory (NUMA).

The IBM p690 Regatta is an example of a high end SMP system. Intel Xeon processors dominated the

multiprocessor market for business PCs and were the only major x86 options until the release of AMD's Opteronrange of processors in 2004. Both ranges of processors had their own onboard cache but provided access to

shared memory; the Xeon processors via a common pipe and the Opteron processors via independent pathways

to the system RAM.

Chip multiprocessors, also known as multi-core computing, involves more than one processor placed on a single

chip and can be thought of the most extreme form of tightly-coupled multiprocessing. Mainframe systems with

multiple processors are often tightly-coupled.

Loosely-coupled multiprocessor syst ems are based on multiple standalone single or dual processor commodity

computers interconnected via a high speed communication system (Gigabit Ethernet is common).

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A Linux Beowulf cluster is an example of a loosely-coupled system. Tightly-coupled systems perform better and

are physically smaller than loosely-coupled systems, but have historically required greater initial investment

and may depreciate rapidly; nodes in a loosely-coupled system are usually inexpensive commodity computer

and can be recycled as independent machines upon retirement from the cluster. Power consumption is also a

consideration. Tightly-coupled systems tend to be much more energy efficient than clusters. This is because

considerable economy can be realized by designing components to work together from the beginning in tightly

coupled systems, whereas loosely-coupled systems use components that were not necessarily intended

specifically for use in such systems.

Operating System Support: Each processor in a multiprocessor is capable of executing work independently o

the others. Separate, independent threads may be dispatched, one per processor, and run in parallel. Only one

copy of the Windows 2000 operating system is running, controlling what runs on all the processors. From a

performance monitoring perspective, you will see multiple instances of the processor object reported in bot

Task manager and System Monitor.

The specific type of multiprocessor support offered beginning in Windows NT 4.0 is known as symmetric

multiprocessing, often abbreviated as SMP. Symmetric in this context, means that every thread is eligible to

execute on any processor. Prior to NT 4.0, Windows NT supported only asymmetric multiprocessing. In an NT

3.5x machine, interrupts could only be processed on CPU 0. CPUs 1, 2, 3, could only run user and kernel code

never interrupt service routines (ISRs) and Deferred Procedure Calls (DPCs). This asymmetry ultimately limits the

scalability of NT 3.5x multiprocessor systems, because the CPU 0 engine is readily overloaded under some

workloads while the remaining microprocessors are idling. In an SMP, in theory, all the microprocessors should

run out of capacity at the same time. One of the key development projects associated with the NT 4.0 release

was changes to the kernel to support SMPs. In addition, the development team fine-tuned the OS code to run

much better in a multiprocessing environment. (Later in this chapter, we discuss some of the coding technique

that are appropriate in a multiprocessing environment.) Windows 2000 also incorporates further improvements

inside the operating system to boost performance on large n-way multiprocessor configurations.

Thread scheduling: Since multiple programs are loaded in Windows 2000 memory anyway, it seems like it

should be a relatively simple matter for Windows 2000 to run two (or three or four or eight) programs at a time.

Unfortunately, shared-memory and coordination issues associated with the need to maintain cache coherence

make things considerably more complicated. Even though the separate processors operate largely

independently of each other, there are some occasions where the hardware must communicate and coordinate

There are also times when it is necessary to prevent multiple independent processors from running in parallel

Indeed, shared memory multiprocessors require some mechanism to ensure that threads execute serially as

they access and update global shared-memory data structures. A brief look at how the Windows 2000 Schedule

works in a multiprocessor configuration will illustrate the data integrity concerns. It will also serve both to

highlight the cache coherence problem and put the performance implications of multiprocessing into

perspective.

The Windows 2000 OS kernel is multithreaded, which means it is capable of working in parallel if the hardware iavailable. During installation, the presence of a multiprocessor is detected and a multiprocessing version of

ntoskrnl.exe, the OS kernel, is loaded. During OS initialization, about 20 additional kernel threads are allocated

for each additional processor that is detected. Windows 2000 internal data structures provide native support fo

up to 32 processing engines. Meanwhile, Windows 2000 maintains a single copy of the Scheduler's dispatching

queue for ISRs, DPCs, and kernel and normal program threads that is shared across all processors. There is only

one Dispatcher Ready Queue, even on a multiprocessor.

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Processor affinity: Logically, the structure of the Ready Queue and the relative priority of threads waiting to

execute is identical whether Windows 2000 is executing on an single processor or on multiple processors. The

main difference is that multiple threads can run concurrently on a multiprocessor, a little detail that leads to

many complications. In the regular course of events, the Windows 2000 Scheduler selects the highest priority

waiting thread to run on each available processor. In addition, certain execution threads may have an affinity to

execute on specific processors. Windows 2000 supports both hard affinity , where a given thread is eligible to

run only on specific processors, and soft affinity , where Windows 2000 favors scheduling specific threads on

specific processors, usually for performance reasons.

Hard affinity is specified at the process and thread level using a processor affinity mask. The Win32 API calls to

accomplish this are straightforward. First, a thread issues a Get Process Affinity Mask call referencing a process

handle, which returns a 32-bit System Affinity Mask. Each bit in the System Affinity Mask represents a

configured processor. Then, the program calls Set Process Affinity Mask with a corresponding 32-bit affinity

mask that indicates the processors that threads from the process can be dispatched on. Figure 5-4 illustrates the

use of this function in Task man, which allows you to set a process's affinity mask dynamically, subject to the

usual security restrictions that allow Task man to operate only on foreground-eligible processes by default

There is a corresponding Set Thread Affinity Mask call to override the process settings for specific threads. Once

hard affinity is set, threads are eligible to be dispatched only on specific processors. This chapter concludes with

a section discussing when setting a processor affinity mask for certain applications can be very desirable fo

performance reasons. Along the way, it is necessary to tackle several related multiprocessing topics to conside

this important configuration and tuning strategy.

Figure 5-4. Setting a process's processor affinity mask using Task man

Suppose that following an interrupt, an application program thread becomes ready to run, and multiple

processors are idle. First, Windows 2000 must select the processor on which to run the ready thread. This

decision is based on performance. If the thread was previously dispatched within the last Scheduler quantum

(you remember the Scheduler time-slice quantum, don't you?), Windows 2000 attempts to schedule the thread

on that processor, which works as long as the current thread has a higher priority than the thread that is already

running there or the ideal processor happens to be idle. This is known as soft affinity. By scheduling the thread

back on the same processor where it just ran, Windows 2000 hopes that a good deal of the thread's code and

data from the previous execution interval are still present in that processor's cache. The difference in instruction

execution rate between a cache "cold start," when a thread is forced to fault its way through its frequently

accessed code and data, and a "warm start," when the cache is preloaded, can be substantial. However

Windows 2000 is willing to schedule the waiting thread on a different processor if the desired processor is busy

with a higher-priority task.

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Serialization and locking: The Scheduler code in Windows 2000 can run in multiple threads concurrently

Therefore, Windows 2000 must ensure that two processors do not try and run the same ready thread at the

same time. This is just one example of a more general integrity issue in a multiprocessor. Because shared

memory data structures can be accessed by multiple threads concurrently, a serialization or locking mechanism

is necessary to ensure that independent processors do not, for example, select the same thread off the Ready

Queue at the same time. To prevent this, the shared-memory locations associated with the Windows 2000

Scheduler's dispatching queue are locked so that threads are only added or removed from the Ready Queue one

at a time. We look at this serialization mechanism more closely in a moment. Serialization services are one ofthe key functions performed by the Windows 2000 operating system. (The current fashion in OS design is tha

about the only function performed in the low-level operating system microkernel is serialization. That is how

fundamental serialization and locking are!) Windows 2000 must ensure that kernel threads running on multiple

processors serialize before accessing its shared internal data structures. Windows 2000 also provides

serialization services to application programs with similar requirements.

Shared-memory multiprocessor programming model: One reason shared-memory multiprocessors are so

popular is that, with minor exceptions, programs that run on uniprocessors can run unmodified on shared

memory multiprocessors. In additionally, almost any multithreaded application will likely benefit from having a

choice of processors to run on--any thread can run on any available processor in an SMP. However, extreme

care must be exercised to prevent multiple threads in your application from accessing and changing shared data

structures in parallel. To help developers, the Windows 2000 operating system provides a complete set o

platform-independent serialization services, courtesy of the HAL, for use by both application programs and

kernel mode drivers. These thread synchronization services are used to ensure that Windows 2000 application

are "thread-safe," i.e., capable of executing correctly on a multiprocessor. This set of thread synchronization

services allows programmers to implement complex, multithreaded applications without having to understand

the underlying hardware mechanisms on a multiprocessor, which are platform-specific. Understanding the

performance ramifications of shared-memory multiprocessors does require some knowledge of the hardware

task 1.pdf

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