User's view and Systems view

User's View

The user view of the computer varies by the interface being used. Most computer users sit in front of a PC, consisting of a monitor, keyboard, mouse and system unit. Such a system is designed for one user to monopolize its resources, to maximize the work that the user is performing. In this case,the operating system is designed mostly for ease of use, with some attention paid to performance, and none paid to resource utilization.

Some users sit at a terminal connected to a mainframe or minicomputer. Other users are accessing the same computer through other terminals. These users share resources and may exchange information. The operating system is designed to maximize resource utilization.

Other users sit at workstations, connected to networks of other workstations and servers. These users have dedicated resources at their disposal, but they also share resources such as networking and servers.

Recently, many varieties of handheld computers have come into fashion. These devices are mostly standalone, used singly by individual users. Some are connected to networks, either directly by wire or through wireless modems. Due to power and interface limitations they perform relatively few remote operations. These operating systems are designed mostly for individual usability, but performance per amount of battery life is important as well.

Some computers have little or no user view. For example, embedded computers in home devices and automobiles may have numeric keypad, and may turn indicator lights on or off to show status, but mostly they and their operating systems are designed to run without user intervention.

Systems View

We can view an operating system as a resource allocator. A computer system has many resources - hardware and software - that may be required to solve a problem. The operating system acts as the manager of these resources.

An operating system can also be viewed as a control program that manages the execution of user programs to prevent errors and improper use of the computer. It is especially concerned with the operation and control of I/O devices.

We have no universally accepted definition of what is part of the operating system. A simple viewpoint is that it includes everything a vendor ships when you order “the operating system”.

A more common definition is that the operating system is the one program running at all times on the computer (usually called the kernel), with all else being application programs. This is the one that we generally follow.

Goals of OS

It is easier to define an operating system by what it does than what it is, but even this can be tricky. The primary goal of some operating system is convenience for the user. The primary goal of other operating system is efficient operation of the computer system. Operating systems and computer architecture have influenced each other a great deal. To facilitate the use of the hardware, researchers developed operating systems. Users of the operating systems then proposed changes in hardware design to simplify them. In this short historical review, notice how identification of operating-system problems led to the introduction of new hardware features.

• To hide details of hardware by creating abstraction
  An abstraction is software that hides lower level details and provides a set of higher-level functions. An operating system transforms the physical world of devices, instructions, memory, and time into virtual world that is the result of abstractions built by the operating system. There are several reasons for abstraction.
  First, the code needed to control peripheral devices is not standardized. Operating systems provide subroutines called device drivers that perform operations on behalf of programs for example, input/output operations.
  Second, the operating system introduces new functions as it abstracts the hardware. For instance, operating system introduces the file abstraction so that programs do not have to deal with disks.
  Third, the operating system transforms the computer hardware into multiple virtual computers, each belonging to a different program. Each program that is running is called a process. Each process views the hardware through the lens of abstraction.
  Fourth, the operating system can enforce security through abstraction.


• To allocate resources to processes (Manage resources)
  An operating system controls how processes (the active agents) may access resources (passive entities).
  
  
• Provide a pleasant and effective user interface
  The user interacts with the operating systems through the user interface and usually interested in the “look and feel” of the operating system. The most important components of the user interface are the command interpreter, the file system, on-line help, and application integration. The recent trend has been toward increasingly integrated graphical user interfaces that encompass the activities of multiple processes on networks of computers.

Batch processing - is execution of a series of programs ("jobs") on a computer without human interaction.

Batch jobs are set up so they can be run to completion without human interaction, so all input data is preselected through scripts or command line - parameters. This is in contrast to "online" or interactive programs which prompt the user for such input. A program takes a set of data files as input, process the data, and produces a set of output data files. This operating environment is termed as "batch processing" because the input data are collected into batches on files and are processed in batches by the program.

Multiprogrammed Systems - a number of programs were resident in memory and the CPU could choose which one to run. One way to choose is to just keep executing the current program until an I/O delay is pending - instead of just waiting, the CPU would move onto the next program ready to be run.

• Keep multiple jobs resident in memory
• OS chooses which job to run
• When job waits for I/O switch to another resident job

Result: Job scheduling policies, Memory management and protection, improves throughput and utilization, still not interactive.

Time-Sharing Systems Interactive Computing - while multiprogrammed systems used resources more efficiently i.e. minimized CPU idle time, a user could not interact with a program. By having the CPU switch between jobs at relatively short intervals, we can obtain an interactive system.That is, a system in which a number of users are sharing the CPU (or other critical resource) with a timing interval small enough not to be noticed e.g. no more than 1 second. We say that a time-sharing system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time-shared computer.

• The CPU multiplexed among several jobs in memory and on disk (CPU allocated only to jobs in memory). The CPU switches to the next job that can be run whenever the current job enters a wait state or after the current job has used a standard unit of time.When viewed over a relatively long time frame, we obtain the appearance that the CPU is simultaneously running multiple programs.
• Job swapped in and out of memory to disk. If the time-sharing computer does not have enough semiconductor memory installed to hold all of the desired programs, then a backing store must be used to temporarily hold the contents relating to some programs when other programs are present in semiconductor memory. In effect, we are now ``memory sharing'' between competing users (programs). This idea leads to a mechanism called virtual memory.
• On-line communication between user and system provided; when OS finishes execution of a command, it awaits next ``control statement'' from user.

The sensible sharing of resources such as CPU time and memory must be handled by the operating system, which is just another program running on the computer. For this control program to always be in control, we require that it never be blocked from running. The operating system, which might in fact be organized like a small number of cooperating programs, will lock itself into memory and then control CPU allocation priority in order that it never be blocked from running.

Advantages of Parallel System

In terms of disproportionality, Parallel systems usually give results which fall somewhere between pure plurality/majority and pure PR systems. One advantage is that, when there are enough PR seats, small minority parties which have been unsuccessful in the plurality/majority elections can still be rewarded for their votes by winning seats in the proportional allocation. In addition, a Parallel system should, in theory, fragment the party system less than a pure PR electoral system.

It is much faster than sequential processing when it comes to doing repetitive calculations on vast amounts of data. This is because a parallel processor is capable of multithreading on a large scale, and can therefore simultaneously process several streams of data. This makes parallel processors suitable for graphics cards since the calculations required for generating the millions of pixels per second are all repetitive. GPUs can have over 200 cores to help them in this.The CPU of a normal computer is a sequential processor - it's good in processing data one step at a time. This is needed in cases where the calculation the processor is performing depends on the result of the previous calculation and so on; in parallel processing these kinds of calculations will slow it down, which is why CPUs are generally optimised for sequential operations and have only 1-8 cores.In summary, the one advantage of parallel processing is that it is much faster (about 200 times faster in the best cases) for simple, repetitive calculations on vast amounts of similar data.

Symmetric and Asymmetric Multiprocessing

The difference between symmetric and asymmetric multiprocessing:

Asymmetric multiprocessing - In asymmetric multiprocessing (ASMP), the operating system typically sets aside one or more processors for its exclusive use. The remainder of the processors run user applications. As a result, the single processor running the operating system can fall behind the processors running user applications. This forces the applications to wait while the operating system catches up, which reduces the overall throughput of the system. In the ASMP model, if the processor that fails is an operating system processor, the whole computer can go down.

Symmetric Multiprocessing - Symmetric multiprocessing (SMP) technology is used to get higher levels of performance. In symmetric multiprocessing, any processor can run any type of thread. The processors communicate with each other through shared memory.

SMP systems provide better load-balancing and fault tolerance. Because the operating system threads can run on any processor, the chance of hitting a CPU bottleneck is greatly reduced. All processors are allowed to run a mixture of application and operating system code. A processor failure in the SMP model only reduces the computing capacity of the system.

SMP systems are inherently more complex than ASMP systems. A tremendous amount of coordination must take place within the operating system to keep everything synchronized. For this reason, SMP systems are usually designed and written from the ground up.

All processors of symmetric multiprocessing are peers; the relationship between processors of asymmetric multiprocessing is a master-slave relationship. More specifically, each CPU in symmetric multiprocessing runs the same copy of the OS, while in asymmetric multiprocessing, they split responsibilities typically, therefore each may have specialized (different) software and roles.

Client Server and Peer-to-Peer Systems

Client-Server System

Client-server systems are not limited to traditional computers. An example is an automated teller machine (ATM) network. Customers typically use ATMs as clients to interface to a server that manages all of the accounts for a bank. This server may in turn work with servers of other banks (such as when withdrawing money at a bank at which the user does not have an account). The ATMs provide a user interface and the servers provide services, such as checking on account balances and transferring money between accounts.

A server based network.

To provide access to servers not running on the same machine as the client, middleware is usually used. Middleware serves as the networking between the components of a client-server system; it must be run on both the client and the server. It provides everything required to get a request from a client to a server and to get the server's response back to the client. Middleware often facilitates communication between different types of computer systems. This communication provides cross-platform client-server computing and allows many types of clients to access the same data.

or groupware system.

Peer-to-Peer System

Peer-to-peer (P2P) networking is a method of delivering computer network services in which the participants share a portion of their own resources, such as processing power, disk storage, network bandwidth, printing facilities. Such resources are provided directly to other participants without intermediary network hosts or servers. Peer-to-peer network participants are providers and consumers of network services simultaneously, which contrasts with other service models, such as traditional client-server computing.

A peer-to-peer based network.

P2P networks are typically used for connecting nodes via largely ad hoc connections. Such networks are useful for many purposes. Sharing content files containing audio, video, data or anything in digital format is very common, and real time data, such as telephony traffic, is also passed using P2P technology.

Stand Alone PC and Workstation

Stand Alone PC - stand alone operating system is a system that is independent of another for example windows 3.1 ,95,98 were all a shell based on the ms-dos operating system to put it in simpler terms windows was a dressed up version of ms-dos with all the bells and whistles to be more appealing to the eye and be more user friendly . later versions of windows were independent of the ms-dos operating system hence they are known as "stand alone operating systems" .

Workstation - a type of computer used for engineering applications (CAD/CAM),desktop publishing, software development, and other types of applications that require a moderate amount of computing power and relatively high quality graphics capabilities.

Workstations generally come with a large, high-resolution graphics screen, at least 64 MB (megabytes) of RAM, built-in network support, and a graphical user interface. Most workstations also have a mass storage device such as a disk drive, but a special type of workstation, called a diskless workstation, comes without a disk drive. The most common operating systems for workstations are UNIX and Windows NT.

In terms of computing power, workstations lie between personal computers and minicomputers, although the line is fuzzy on both ends. High-end personal computers are equivalent to low-end workstations. And high-end workstations are equivalent to minicomputers.

Like personal computers, most workstations are single-<user computers. However, workstations are typically linked together to form a local-area network, although they can also be used as stand-alone systems.

In networking, workstation refers to any computer connected to a local-area network. It could be a workstation or a personal computer.

Essential Properties of OS

Batch - group of jobs submitted to machine together. A job was originally presented to the machine (and its human operator) in the form of a set of cards - these cards held information according to how ``punched'' out of the cardboard. The operator grouped all of the jobs into various batches with similar characteristics before running them (all the quick jobs might run, then the slower ones, etc.).

• Operator collects job, orders efficiently, runs one at a time
• Amortize setup costs over many jobs
• Keep machine busy while programmer thinks
• User must wait for results until batch collected and submitted

Result: Improved system throughput and utilization, but lost interactivity.

Time-sharing - is sharing a computing resource among many users by multitasking. Its introduction in the 1960s, and emergence as the prominent model of computing in the 1970s, represents a major historical shift in the history of computing. By allowing a large number of users to interact simultaneously on a single computer, time-sharing dramatically lowered the cost of providing computing, while at the same time making the computing experience much more interactive.

It refers to the concurrent use of a computer by more than one user -- users share the computer's time. Time sharing is synonymous withmulti-user. Almost all mainframes and minicomputers are time-sharingsystems, but most personal computers and workstations are not.

Real time - occurring immediately. The term is used to describe a number of different computer features. For example, real-time operating systemsare systems that respond to input immediately. They are used for such tasks as navigation, in which the computer must react to a steady flow of new information without interruption. Most general-purpose operating systems are not real-time because they can take a few seconds, or even minutes, to react.

Real time can also refer to events simulated by a computer at the same speed that they would occur in real life. In graphics animation, for example, a real-time program would display objects moving across thescreen at the same speed that they would actually move.

Network - is a group of two or more computer systems linked together. There are many types of computer networks, including:

local-area networks (LANs) : The computers are geographically close together (that is, in the same building).

wide-area networks (WANs) : The computers are farther apart and are connected by telephone lines or radio waves.

campus-area networks (CANs): The computers are within a limited geographic area, such as a campus or military base.

metropolitan-area networks MANs): A data network designed for a town or city.

home-area networks (HANs): A network contained within a user's home that connects a person's digital devices.

In addition to these types, the following characteristics are also used to categorize different types of networks:

topology : The geometric arrangement of a computer system. Common topologies include a bus, star, and ring. See theNetwork topology diagrams in the Quick Reference section of Webopedia.

protocol : The protocol defines a common set of rules and signals that computers on the network use to communicate. One of the most popular protocols for LANs is called Ethernet. Another popular LAN protocol for PCs is the IBM token-ring network .

architecture : Networks can be broadly classified as using either a peer-to-peer or client/server architecture.

Computers on a network are sometimes called nodes. Computers anddevices that allocate resources for a network are called servers.

Distributed - refers to any of a variety of computer systems that use more than onecomputer, or processor, to run an application. This includes parallel processing, in which a single computer uses more than one CPU toexecute programs. More often, however, distributed processing refers tolocal-area networks (LANs) designed so that a single program can run simultaneously at various sites. Most distributed processing systemscontain sophisticated software that detects idle CPUs on the networkand parcels out programs to utilize them.

Another form of distributed processing involves distributed databases,databases in which the data is stored across two or more computer systems. The database system keeps track of where the data is so that the distributed nature of the database is not apparent to users.

Handheld - is a portable computer that is small enough to be held in one's hand. Although extremely convenient to carry, handheld computers have not replaced notebook computers because of their small keyboards and screens. The most popular hand-held computers are those that are specifically designed to provide PIM (personal information manager)functions, such as a calendar and address book.

Some manufacturers are trying to solve the small keyboard problem by replacing the keyboard with an electronic pen. However, these pen-based devices rely on handwriting recognition technologies, which are still in their infancy.