7.2. Standard Windows Architectures

7.2.1. Windows 9x architecture

The windows architecture (Win 9x way) looks like this:

+---------------------+        \
|     Windows EXE     |         } application
+---------------------+        /

+---------+ +---------+        \
| Windows | | Windows |         \ application & system DLLs
|   DLL   | |   DLL   |         /
+---------+ +---------+        /

+---------+ +---------+      \
|  GDI32  | | USER32  |       \
|   DLL   | |   DLL   |        \
+---------+ +---------+         } core system DLLs
+---------------------+        /
|     Kernel32 DLL    |       /
+---------------------+      / 

+---------------------+        \
|     Win9x kernel    |         } kernel space
+---------------------+        /

+---------------------+       \
|  Windows low-level  |        \ drivers (kernel space)
|       drivers       |        /
+---------------------+       /
	  

7.2.2. Windows NT architecture

The windows architecture (Windows NT way) looks like the following drawing. Note the new DLL (NTDLL) which allows implementing different subsystems (as win32); kernel32 in NT architecture implements the Win32 subsystem on top of NTDLL.

+---------------------+                      \
|     Windows EXE     |                       } application
+---------------------+                      /

+---------+ +---------+                      \
| Windows | | Windows |                       \ application & system DLLs
|   DLL   | |   DLL   |                       /
+---------+ +---------+                      /

+---------+ +---------+     +-----------+   \
|  GDI32  | |  USER32 |     |           |    \
|   DLL   | |   DLL   |     |           |     \
+---------+ +---------+     |           |      \ core system DLLs
+---------------------+     |           |      / (on the left side)
|    Kernel32 DLL     |     | Subsystem |     /
|  (Win32 subsystem)  |     |Posix, OS/2|    /
+---------------------+     +-----------+   / 

+---------------------------------------+
|               NTDLL.DLL               |
+---------------------------------------+

+---------------------------------------+     \
|               NT kernel               |      } NT kernel (kernel space)
+---------------------------------------+     /
+---------------------------------------+     \
|       Windows low-level drivers       |      } drivers (kernel space)
+---------------------------------------+     /
	  

Note also (not depicted in schema above) that the 16 bit applications are supported in a specific subsystem. Some basic differences between the Win9x and the NT architectures include:

• Several subsystems (Win32, Posix...) can be run on NT, while not on Win 9x

• Win 9x roots its architecture in 16 bit systems, while NT is truly a 32 bit system.

• The drivers model and interfaces in Win 9x and NT are different (even if Microsoft tried to bridge the gap with some support of WDM drivers in Win 98 and above).