OPERATING SYSTEM OVERVIEW

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OPERATING SYSTEM OVERVIEW

• Operating systems are programs designed to
  control the operation of a computer system. As a
  group, they are easily some of the most complex
  programs created.

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OPERATING SYSTEM OVERVIEW

• Every portion of the system must be controlled
  and coordinated so that the millions of
  operations that occur every second are carried
  out correctly and on time.
• In addition, it is the job of the operating
  system to make the complexity of the PC as
  invisible as possible to the user.

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OPERATING SYSTEM OVERVIEW

• The operating system acts as an intermediary
  between nearly as complex software applications,
  and the hardware they run on.
• Finally, the operating system accepts commands
  from the computer user and carries them out to
  perform some desired operation.

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OPERATING SYSTEM OVERVIEW

• This control is so precise that for applications
  to run correctly, they must be written within the
  control parameters of an OS, and are not portable
  to other OSs.
• For example, an application, such as Microsoft
  Excel written for Windows NT 4, will not function
  on an UNIX computer.

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OPERATING SYSTEM OVERVIEW

• Literally thousands of different operating
  systems are in use with microcomputers. The
  complexity of each operating system typically
  depends on the complexity of the application the
  microcomputer is designed to fill.

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OPERATING SYSTEM OVERVIEW

• The operating system for a fuel mixture
  controller in an automobile is relatively simple,
  but an operating system for a multi-user computer
  system that controls many terminals is relatively
  complex.

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OPERATING SYSTEM OVERVIEW

• In the large, multi-user system, the operating
  system is likely to be stored on disk and have
  sections loaded into RAM when needed.
• This type of operating system must control
  several pieces of hardware, manage files created
  and used by various users, provide security for
  each users information, and manage
  communications between different stations.

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OPERATING SYSTEM OVERVIEW

• A disk operating system (DOS) is a collection of
  programs used to control overall computer
  operation in a disk-based system.
• These programs work in the background to enable
  the user of the computer to input characters from
  the keyboard, to define a file structure for
  storing records, or to output data to a monitor
  or printer. The DOS is responsible for finding
  and organizing your data and applications on the
  disk.

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OPERATING SYSTEM OVERVIEW

• The disk operating system (DOS) can be
  divided into three distinct sections
• Resource management - Manages the hardware
  including CPU, memory, secondary storage, and I/O
  peripherals.
• File management - Controls the creation,
  deletion and access of program and data files.
• Task management - Manages the execution of tasks
  required to accomplish user-directed requests by
  giving each task a slice of CPU time and
  directing CPU interrupts.

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OPERATING SYSTEM OVERVIEW

• Prior to the invention of the network operating
  system, the functionality of network
  communication had to be added to an existing
  operating system.
• This addition usually came in the form of some
  sort of communication software packages or OS
  add-on used to extend the functionality of
  standalone operating systems to be shared with
  other users.

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OPERATING SYSTEM OVERVIEW

• For a system to communicate in a networked
  manner, the original OS and the Network Operating
  System (NOS) extensions had to be present on a
  single computer.
• Microsofts LAN Manager is an excellent example
  of this type of technology. It was an add-on to
  MS-DOS, Windows 3.x, and OS/2 computers to enable
  networked communications.

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OPERATING SYSTEM OVERVIEW

• It wasnt long before true NOSswhich were able
  to manage the activities on both standalone
  computers and network communicationsreplaced OS
  add-ons.
• Such network operating systems include Novells
  NetWare, UNIX and Microsofts Windows 2000.

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OPERATING SYSTEM OVERVIEW

• NOSs require a lot of computing power.
• To get the most power out of a hardware
  configuration, many network operating systems,
  and some non-network operating systems, make use
  of a process called multitasking, which allows an
  operating system to run numerous
  processescontrol more than one task
  simultaneously.

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OPERATING SYSTEM OVERVIEW

• A true multitasking OS is able to support as
  many simultaneous processes as there are CPUs.
  However, when a computer only
• has one CPU, multitasking can be simulated
  through a technique called time slicing.

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OPERATING SYSTEM OVERVIEW

• Time slicing involves dividing CPU computing
  cycles (hundreds to millions of cycles per
  second) between multiple tasks.
• You do this by giving each task a certain amount
  of process cycles, then halting that task to make
  the next task active. This process repeats until
  each task is finished.

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OPERATING SYSTEM OVERVIEW

• It is important to note that there are two types
  of multitasking
•  
• Preemptive -The operating system controls which
  processes are
• allowed access to the CPU and for how long. Once
  the assigned
• time slice expires, the current process is
  halted and the next
• process is given its computing time.
•  
• Cooperative -The operating system cannot stop a
  process once
• CPU control is given to a process, it retains
  control until the
• process is complete. During this time, no other
  process is allowed to access the CPU

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OPERATING SYSTEM OVERVIEW

• A true high-performance NOS employs preemptive
  multitasking. Otherwise, the NOS couldnt
  complete many time-dependent tasks and would fail
  to complete tasks repeatedly.

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OPERATING SYSTEM OVERVIEW

• An important issue for Network Operating Systems
  is the ability to restrict access to network
  resources. This is called network security.
• It provides the means to control which resources
  users can access, the extent of that access, and
  how many users can access that resource
  simultaneously at any given time. This control
  provides privacy and protection, and maintains an
  efficient networking environment.

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OPERATING SYSTEM OVERVIEW

• In addition to providing control of network
  resources, a NOS does the following
•  
• - Provides logon authentication for users 
• - Manages users and groups 
• - Stores management, control, and auditing tools
  for network administration 
• - Provides fault tolerance for protection of
  network integrity

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OPERATING SYSTEM OVERVIEW

• System-wide services are the main facility a
  network operating system provides. These services
  come in many flavors and types.
• Services are functions provided by the operating
  system and forms a backbone used by those
  applications, which need to interact beyond the
  simplistic boundaries imposed by the process
  concept.

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OPERATING SYSTEM OVERVIEW

• A service is provided by a server and accessed
  by clients. A server is a process or task that
  continuously monitors incoming service requests
  (similar to telephone operators).
• When a service request comes in, the server
  process reacts to the request, performs the task
  requested and then returns a response to the
  requestor.

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OPERATING SYSTEM OVERVIEW

• Often, one or more such server processes run on
  a computer and the computer is called a server.
  However, a server process does not have to run on
  a server and the two terms are often, confusingly
  used interchangeably.

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OPERATING SYSTEM OVERVIEW

• Network operating systems do provide a set of
  static, predefined services, or system calls like
  the regular operating system, but in addition
  provides a much larger, richer set of dynamically
  creatable and configurable services.

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OPERATING SYSTEM OVERVIEW

• Any process making a request to a server process
  is called a client. A client makes a request by
  sending a message to a server containing details
  of the request and awaiting a response.
• For each server, there is a well-defined
  protocol defining the requests that can be made
  to that server and the responses that are
  expected. In addition, any process can make a
  request that is anyone can become a client, even
  temporarily.

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OPERATING SYSTEM OVERVIEW

• Services provided by a network operating system
  include file service, name service, object
  service, time service, memory service and so on.

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OPERATING SYSTEM OVERVIEW

• The following is a listing of the more common
  operating systems that have been used in the past
  along with the more recent models

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OPERATING SYSTEM OVERVIEW

• DOS
• 16-bit operating system, originally single-user,
  single task, limited ability to share resources
  across machines.
• Version 3.1 introduced some multi-user
  functions, thus, a network operating system (NOS)
  could access DOS functions like file management
  and record-blocking.

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OPERATING SYSTEM OVERVIEW

• OS/2
• Originally developed by IBM and Microsoft.
• 32-bit operating system.
• True multitasking.
• OS/2 Warp Connect includes networking
  capabilities.

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OPERATING SYSTEM OVERVIEW

• Windows for Workgroups 3.11
• Operating environment (not an operating system)
  working with DOS.
• E-mail.
• Scheduling.
• Peer-to-peer networking.
• Easy to attach to Novell Netware or LAN Manager.

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OPERATING SYSTEM OVERVIEW

• Windows 98
• Designed to run 16-bit and 32-bit applications.
• True multitasking.
• Built-in TCP/IP and PPP.
• Users who do not need the heavy duty features
  and requirements of NT.
• plug and play concept to allow users to add
  peripheral devices.

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OPERATING SYSTEM OVERVIEW

• Windows NT (New Technology)
• 32-bit operating system designed to support
  client operations in a distributed environment.
• Built-in support for TCP/IP and SNMP network
  management.
• Built-in file-sharing and printer sharing
  capabilities.
• APIs (application program interface) and RPCs
  (remote procedure call) for transparent
  interfacing to distributed applications.

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OPERATING SYSTEM OVERVIEW

• Windows 2000 Advanced Server
• Easy to integrate with Windows running on
  desktop PCs.
• Strong tools like Visual Basic, Visual C, OLE.
  
• Offers remote access for up to 64 incoming
  ports.
• Runs on different processor architectures.
• Limitations in terms of scalability.

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OPERATING SYSTEM OVERVIEW

• Novell NetWare
• Novell Directory Services (NDS)
• Global, hierarchical, object-oriented naming
  service that allows replication and distribution.
  
• Enhanced security.
• File compression and data migration.

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OPERATING SYSTEM OVERVIEW

• Novell Netware (cont..)
• Its own proprietary nonstandard, non layered set
  of network protocols.
• NLMs (Netware Loadable Modules) can be added to
  enhance network services.
• Fast for transaction processing.

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OPERATING SYSTEM OVERVIEW

• UNIX
• Supports multiple users, multiple tasks, open
  architecture, multiple platforms.
• TCP/IP is its internet suite of protocols.
• Choice for LAN servers running large databases
  and other enterprise-scale jobs.