Windows NT architecture.ppt

CIS 620

Advanced Operating

Systems

Lecture 12 – Windows Architecture

Prof. Timothy Arndt

Windows NT Design Goals

• Windows NT had a number of design goals:

 Compatibility: Windows 95 interface, support

for the FAT file system, MS-DOS, OS/2,

Windows 3.x and POSIX applications and for a wide variety of devices and networks.

 Portability: Windows NT runs on both CISC

and RISC processors.

 Scalability: NT takes full advantage of

Windows NT Design Goals

 Security: Windows NT has a uniform security

architecture designed to provide a safe environment to run mission-critical

applications. It has met the requirements for C2 level security.

 Distributed Processing: NT is designed with

networking built into the base OS. NT supports a number of transport protocols and named

Windows NT Design Goals

 Reliability and Robustness: this means that the

architecture must protect the OS and

applications from damage. Applications cannot read or write outside of their own address

space. The OS is isolated from applications.

 Localization: NT is offered in many countries

around the world, in local languages, and supports Unicode.

 Extensibility: the modular design of NT allows

Windows NT Architectural

Modules

 Windows NT 4.0 architecture is divided into

two main sections: user mode and kernel mode.

• Kernel mode is a highly privileged mode of

operation in which the code has direct access to all hardware and all memory, including the address spaces of all user processes. The part of Windows NT running in kernel mode is called the Windows NT Executive. It includes the the Hardware

Windows NT Architectural

Modules

• User mode is a less privileged processor mode with no direct access to hardware. Code running in user mode acts directly only in its own address space. It uses well-defined operating system application

program interfaces (APIs) to request system

services. The environment and integral subsystems run in user mode.

• In Windows NT 4.0, the Windows Manager, the Graphics Device Interface (GDI), and graphics device drivers have been moved from the Win32 subsystem to the Windows NT Executive. This was done to improve performance, but it reduces the

Windows NT Architectural

Modules

 Windows NT 4.0 moves further away from a

pure microkernel architecture.

 Pure microkernel architectures are modular,

and they keep the number of components running in kernel mode to a minimum.

 These architectures are inherently more

reliable, but they may suffer from performance problems due to constant context switches.

 Windows NT is a modified microkernel

Windows NT 3.51

Architecture

Manager File Systems

I/O Manager Cache Manager Device Drivers Network Drivers Microkernel NT Executive

Hardware Abstraction Layer (HAL)

Namespace and Object

Management

 An OS namespace gives applications the ability

to identify and share resources. The file-system namespace is a well known part. Other

resources include synchronization resources and shared memory.

 NT’s Object Manager subsystem implements

NT’s namespace.

• The Object Manager is a collection of kernel

Namespace and Object

Management

• Kernel subsystems define Object Manager objects to represent the subsystem’s resource types, and rely on the Object Manager’s support routines for

naming and security.

• Processes are represented as process objects, files as file objects, etc.

• The Object Manager notifies subsystems that own an object when applications close, open, or query the object. This is done via method functions

registered when the object type is defined. • In response, subsystems can perform actions

Namespace and Object

Management

 UNIX’s object-tracking mechanism is not as

formal as NT’s. It is based on i-nodes.

 Remember that files represent devices and

sockets as well as “normal” files.

 The kernel notifies file system drivers of actions

that applications perform on i-nodes.

 This is done by calling functions registered in a

table that the file system associates with i-nodes.

Process Management

 NT and UNIX are time-sharing OSs that try to

divide CPU time fairly between applications competing for the CPU.

 Neither OS is suitable for a “hard” real-time

environment.

 NT defines an application using a process

object, which serves as a container for all information about the application.

Process Management

 The NT scheduler divides time between threads

(not between applications). Applications can create additional threads, and all of an

application’s threads share resources and memory space.

 The scheduler attempts to give CPU time to the

highest-priority thread available.

 There are two classes of threads: dynamic (with

Process Management

 Real-time priority values are fixed; the

scheduler does not adjust those priority values.

• Typically, only a few OS-owned threads execute in the real-time range.

 Same priority threads are scheduled in a

preemptive, round-robin manner.

 The NT scheduler can also preempt the kernel.

Further, multiple threads can execute kernel code on separate CPUs.

Process Management

 Process management in modern UNIX systems

is similar to NT process management.

 UNIX schedulers usually implement three

priority classes - realtime, system, and dynamic - that span priority numbers from 0 to 100.

 The kernels of most UNIX implementations are

fully preemptible and reentrant.

Memory Management

 An OSs memory manager is responsible for

defining virtual address spaces for application code and data, and for sharing the physical

memory resource of the computer among applications.

 NT’s Memory Manager defines a 32-bit virtual

address map for 4GB of virtual memory.

Usually, NT assigns the low 2GB to the user mode and the upper 2GB to the kernel mode.

Memory Management

• Some versions of NT (e.g., NT Server 4.0,

Enterprise Edition) support a switch that changes the virtual address space division to 3GB for user space and 1GB for kernel space.

• The kernel space permanently maps the NT kernel and device drivers, but user-space mapping changes to reflect the map of the currently executing thread.

 NT’s Memory Manager implements

demand-paged virtual memory, in which the Memory Manager brings code and data into physical

Memory Management

 The Memory Manager implements the features

of a modern OS

• Applications can share portions of their address map with other applications.

• Copy-on-write is enabled, for efficient

implementation of shared memory when changes to shared memory need to remain private.

Memory Management

 NT assigns each application an upper and lower limit

on physical memory. NT calls this amount of physical

memory the application’s working set.

 When an application reaches its working set’s upper

limit and accesses more code or data, the Memory Manager uses a least-recently-used algorithm to find data in the working set to replace.

Memory Management

 Some define an even split between user and

kernel space and some give the majority to applications, leaving only a few hundred MB for the kernel.

• UNIX memory managers differ from NT in that they manage memory globally - they do not constrain

applications to upper and lower limits. The

least-recently-used algorithm is applied to all

applications. This can lead to thrashing.

Security

 NT’s security capabilities have earned it a

C2-capable rating (as a standalone non-networked system).

 The NT Object Manager’s centralized security

support means that the Object Manager can implement any object - including

synchronization objects, shared memory, and files - with security.

 NT can audit successful and failed attempts to

Security

 The traditional UNIX security model is much

less powerful.

 The lack of ACLs and auditing prevent

traditional UNIX from achieving a C2-capable security rating.

• Major UNIX vendors have implemented proprietary versions which implement these features.

Thin-Client Computing

 UNIX has supported thin-client computing

(X-terminals) for many years. Until recently, however, NT was a single user system.

 Thin-client systems allow a terminal to display

applications that run on a server somewhere on the network.

 Citrix modified NT Server 3.51 to let multiple

Thin-Client Computing

 Citrix developed the Independent Computing

Architecture (ICA) protocol to allow clients to communicate with the server.

 A portion of the RAM and disk are allocated to

each session. The OS keeps track of individual user’s activity.

 The OS transmits screen output using ICA to

the client. The client’s keyboard input is transmitted to the server.

Thin-Client Computing

 In 1997, Microsoft licensed ICA technology

from Citrix. Microsoft developed another protocol called Remote Desktop Protocol (RDP).

 RDP runs on Windows CE-based terminals and

Windows-based PCs.

 ICA supports Windows-based PCs and other

thin-client devices.

 RDP is supported in Windows NT Server 4.0,

Thin-Client Computing

 The Object Manager and Virtual Memory manager

have been modified to perform in a multi-user environment.

• Every object name created within a session is

appended with a unique identifier number associated with the individual session that created it (SessionID).

 The fact that all processes share the kernel

address space resulted in kernel resource limitations when supporting multiple

Thin-Client Computing

 In Windows NT Server 4.0, Terminal Server

Edition, these limitations were addressed by creating a special address range in the kernel, called "SessionSpace," that can be mapped on a per-session basis.

 A new Windows NT service called “Terminal

Server” is the controlling process in the Terminal Server architecture.

• It is primarily responsible for session management, initiation, and termination of user sessions and

Thin-Client Computing

 The Terminal Server service is entirely

protocol-independent, so it can function using RDP or a third-party add-on

protocol such as Citrix’s ICA.

 A user mode protocol extension provides

assistance to the Terminal Server

service. It is the responsibility of this component to provide protocol-specific

functions and services, such as licensing, session shadowing, client font