Page 310 - DCAP403_Operating System

Unit 14: Windows 2000

There are three main environment subsystems: Notes
1. Win32 subsystem runs 32-bit Windows applications and also supports Virtual DOS
Machines (VDMs) , which allows MS-DOS and 16-bit Windows 3.1x (Win16) applications
to run on Windows.
2. OS/2 environment subsystem supports 16-bit character-based OS/2 applications and
emulates OS/2 1.3 and 1.x, but not 32-bit or graphical OS/2 applications as used on OS/2
2.x or later.
3. POSIX environment subsystem supports applications that are strictly written to either the
POSIX.1 standard or the related ISO/IEC standards.
The integral subsystem looks after operating system specific functions on behalf of the

environment subsystem. It consists of a security subsystem (grants/denies access and handles
logons), workstation service (helps the computer gain network access) and a server service (lets
the computer provide network services).

Kernel Mode

Kernel mode in Windows 2000 has full access to the hardware and system resources of the
computer. The kernel mode stops user mode services and applications from accessing critical
areas of the operating system that they should not have access to.
The executive interfaces with all the user mode subsystems. It deals with I/O, object management,
security and process management. It contains various components, including:
1. Object Manager: a special executive subsystem that all other executive subsystems must
pass through to gain access to Windows 2000 resources. This is essentially a resource
management infrastructure service that allows Windows 2000 to be an object oriented
operating system.
2. I/O Manager: allows devices to communicate with user-mode subsystems by translating
user-mode read and write commands and passing them to device drivers.
3. Security Reference Monitor (SRM): the primary authority for enforcing the security rules
of the security integral subsystem.
4. IPC Manager: short for Inter-Process Communication Manager, manages the communication
between clients (the environment subsystem) and servers (components of the executive).
5. Virtual Memory Manager: manages virtual memory, allowing Windows 2000 to use the
hard disk as a primary storage device (although strictly speaking it is secondary storage).
6. Process Manager: handles process and thread creation and termination.
7. PnP Manager: handles Plug and Play and supports device detection and installation at
boot time.
8. Power Manager: the power manager coordinates power events and generates power
IRPs.
9. The display system is handled by a device driver contained in Win32k.sys. The Window
Manager component of this driver is responsible for drawing windows and menus while
the GDI (Graphics Device Interface) component is responsible for tasks such as drawing
lines and curves, rendering fonts and handling palettes. Windows 2000 also introduced

alpha blending into the Graphics Device Interface which reflects in the fade effect in
menus.
The Windows 2000 Hardware Abstraction Layer, or HAL, is a layer between the physical
hardware of the computer and the rest of the operating system. It was designed to hide differences
in hardware and therefore provide a consistent platform to run applications on. The HAL
includes hardware specifi c code that controls I/O interfaces, interrupt controllers and multiple
processors.

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