Information Technology Reference
In-Depth Information
Figure H.10 shows an outline of the architecture of NT. It can be seen that only the kernel
mode has access to the hardware. This kernel includes executive services which include
managers (for I/O, interprocess communications, and so on) and device drivers (which con-
trol the hardware). Its parts include:
•
Microkernel - controls basic operating system services, such as interrupt handling and
scheduling.
•
HAL (hardware abstraction layer) - this is a library of hardware-specific programs
which give a standard interface between the hardware and software. This can either be
Microsoft written or manufacturer provided. They have the advantage of allowing for
transportability of programs across different hardware platforms.
•
Win32 window manager - supports Win32, MS-DOS and Windows 3.
x
applications.
Application
User
mode
Kernel mode
NT Executive
Local
procedure
call
facility
Virtual
memory
manager
Win32
window
manager
I/O
manager
Object
manager
Process
manager
Executive
Services
Microkernel
Graphic
device
driver
Device
driver
HAL (Hardware abstraction layer)
Hardware
Figure H.10
NT architecture
H.10.1 MS-DOS support
Windows NT supports MS-DOS-based applications with an NT Virtual DOS Machine
(NTVDM), where each MS-DOS application has its own NTVDM. The NTVDM is started
by the application Ntvdm.exe and when this has started the application communicates with
two system files Ntio.sys (equivalent to IO.SYS) and Ntdos.sys (equivalent to
MSDOS.SYS). Note that the AUTOEXEC.BAT and CONFIG.SYS files have also been re-
placed by Autoexec.nt and Config.nt (which are normally located in
\WINNT\System32
).
Multiple NTVDMs have the advantage of being reliable because if one NTVDM fails
then it does not affect any others. It also allows MS-DOS-based applications to be multi-
tasked. Unfortunately, each NTVDM needs at least 1 MB of physical memory.
Some MS-DOS applications require direct access to the hardware. NT supports this by
