Page 309 - DCAP403_Operating System

Operating System

Notes attacks by using hardware protection for virtual memory, and software protection mechanisms
for operating system resources.

Windows 2000 comes with a native file system; the NTFS file system that recovers automatically

from many kinds of fi le-system errors after a system crash. Windows NT Version 4.0 has a C-2
security classifi cation from the U.S. government, which signifi es a moderate level of protection
from defective software and malicious attacks. Windows 2000 is currently under evaluation by

the government for that classification as well.
Windows 2000 provides source-level compatibility to applications that follow the IEEE 1003.1
(POSIX) standard. Thus, they can be compiled to run on Windows 2000 without changes to the
source code. In addition, Windows 2000 can run the executable binaries for many programs
compiled for Intel X86 architectures running MS-DOS, 16-bitWindows, OS/2, LAN Manager, and
32-bit Windows, by using the environmental subsystems mentioned earlier. These environmental

subsystems support a variety of file systems, including the MSDOS FAT file system; the OS/2

HPFS file system, the ISO9660 CD file system, and NTFS. Windows 2000Õs binary compatibility,

however, is not perfect. In MS-DOS, for example, applications can access hardware ports directly.
For reliability and security, Windows 2000 prohibits such access.
Windows 2000 is designed to afford good performance. The subsystems that constitute Windows

2000 can communicate with one another efficiently by a local-procedure-call facility that provides
high-performance message passing.
Except for the kernel, threads in the subsystems of Windows 2000 can be preempted by higher-
priority threads. Thus, the system can respond quickly to external events. In addition, Windows
2000 is designed for symmetrical multiprocessing: On a multiprocessor computer, several
threads can run at the same time. The current scalability of Windows 2000 is limited, compared
to that of UNIX. As of late 2000, Windows 2000 supported systems with up to 32 CPUs, whereas
Solaris ran on systems with up to 64 processors. Previous versions of NT supported only up to
8 processors.
Windows 2000 is also designed for international use. It provides support for different locales
via the national language support (NLS) API. NLS API provides specialized routines to format
dates, time, and money in accordance with various national customs. String comparisons are
specialized to account for varying character sets. UNICODE is Windows 2000Õs native character
code.
Windows 2000 supports ANSI characters by converting them to UNICODE characters before
manipulating them (8-bit to 16-bit conversion).

14.2 System Components

Windows 2000 is a highly modular system that consists of two main layers: a user mode and a
kernel mode. The user mode refers to the mode in which user programs are run. Such programs
are limited in terms of what system resources they have access to, while the kernel mode has
unrestricted access to the system memory and external devices. All user mode applications access
system resources through the executive which runs in kernel mode.

User Mode

User mode in Windows 2000 is made of subsystems capable of passing I/O requests to the
appropriate kernel mode drivers by using the I/O manager. Two subsystems make up the user
mode layer of Windows 2000: the environment subsystem and the integral subsystem.
The environment subsystem was designed to run applications written for many different types
of operating systems. These applications, however, run at a lower priority than kernel mode
processes.

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