Network Operating Systems

1. Network Operating Systems Windows NT Dr Milan Simic

2. Windows NT Networking • Windows NT operating system was designed with fully integrated networking capabilities. • In MS-DOS, OS/2 and UNIX network capabilities are installed separately from the core of operating system • Windows NT runs across different processor architectures, such as • complex instruction set computing (CISC), like Intel x86 processors and • reduced instruction set computing (RISC), like MIPS, DEC, PowerPC. • Support for single-processor and multi-processor computing • Support for distributed computing • Built-in networking • Industry standard compliance, such as POSIX (portable OS Interface - IEEE standard for OS ) Dr Milan Simic

3. Other Windows NT Features • Modularity • Reliability and Robustness. Applications run in their own address space. OS in the kernel is isolated from applications, which interact with the kernel using only well defined user-mode application programming interfaces (APIs). • Performance, ie speed of activity. • Compatibility: NT supports MS-DOS, OS/2, Windows 3.x and POSIX applications • Security. Dr Milan Simic

4. Client / Server Computing • Client / Server Computing generally means connecting a single user (client) to multiuser, general-purpose servers, with the processing load shared between both. • The clint request services and the server responds by providing the services. • Client/server approach results in a modular OS. • The servers are small and self-contained. • OS components can be distributed across multiple processors on a single CS or across multiple computers on a network (distributed computing). Dr Milan Simic

5. Object Based Computing • Software objects are combination of computer instructions and data that models the behaviour of things. • Object are composed of the following elements: • Attributes, in the form of program variable, • Behaviour, in the form of code modules, or methods, • An identity that distinguishes one object from others. • Objects interact with each other by passing messages. The sending object is known as the client and the receiving object is known as the server. Dr Milan Simic

6. Multitasking and Multiprocessing • Multitasking is sharing a single processor among multiple threads of execution. • Multiprocessing refers to more than one processor. • Muptiprocessing OS can be asymmetric (ASMP) or symmetric (SMP). • In ASMP OS sets aside one or more processors for its exclusive use. Other processors run user applications. • In SMP any processor can run any type of thread. • Windows NT is an SMP system. • SMP systems provide better load-balancing and fault tolerance. Dr Milan Simic

7. Kernel and User Mode • In an OS applications are separated from OS itself. • The OS code runs in a privileged processor mode known as kernel, and has access to the system data and hardware. • Applications run in a nonprivileged processor mode known as user mode and have limited access to system data and hardware through a set of tightly controlled APIs. • Executive is the kernel-mode portion of the Windows NT, and except for a user interface, is a complete OS itself. • Executive components are: I/O manager, Object manager, Security reference monitor, Process manager, Local procedure call facility, VM manager, Window manager, Graphics device interface, Graphics device drivers. Dr Milan Simic

8. Windows NT OS Architecture Dr Milan Simic

9. Protected Subsystems • The protected subsystems are user mode servers. • There are two types: Integral and Environment. • An Integral Subsystem is a server that performs an important system function such as security. • An Environment Subsystem is a server that provides support to applications written for different OSystems. • Windows NT currently supports: • Win32 subsystem as native OS for Windows NT, • POSIX subsystem • OS/2 subsystem Dr Milan Simic

10. Client Network Software • Client network software is the portion of the NOS (Network Operating System) installed on the client computer. • A redirector is a software component on a server, or a client network operating system that operates at the Presentation layer, by examining requests, to determine if the requested resources can be accessed locally, or remotely (network). • A designator is a NOS module that keeps track of the drive letters assigned locally to the remote drives. Dr Milan Simic

11. Server Network Software • Server network software is the NOS installed on the computers that host network resources to be shared. • Server, or Server NOS features: • Protection and allocation of resources, • Management of users and groups, • Logon authentication, • Management, control and auditing tools to administer the network, • Fault tolerance. Dr Milan Simic

12. Network Access • NT Server provides control of what network users can do, while giving them access to resources. The following features control access: • User accounts • User rights • User groups • Subjects and impersonations • Security information about objects ( permission ) Dr Milan Simic

13. Installing a NOS • Issues to be considered before installing a NOS: • Type of network (topology) • Size of network • Job requirements of the server • File systems to be used • Identification or naming conventions • Types of operating systems used on servers and clients • Data storage devices Dr Milan Simic

14. References • Microsoft Windows NT Server Networking Guide, Microsoft Press, 1996 • A guide to Networking Essentials, Tittel Johnson, Course Technology, 1998 Dr Milan Simic