Information Technology Reference
In-Depth Information
•
Task scheduling - the Kernel schedules and runs threads of each process associated with
an application.
•
Provides services to both 16-bit and 32-bit applications by using a thunking process
which is the translation process between 16-bit and 32-bit formats. It is typically used by
a Win16 program to communicate with the 32-bit operating system core.
Virtual memory allows processes to allocate more memory than can be physically allocated.
The operating system allocates each process a unique virtual address space, which is a set of
addresses available for the process's threads. This virtual address space appears to be 4 GB in
size, where 2 GB are reserved for program storage and 2 GB for system storage.
Figure H.9 illustrates where the system components and applications reside in virtual
memory. Its contents are:
•
3 GB-4 GB - all Ring 0 components.
•
2 GB-3 GB - operating system core components and shared DLLs. These are available to
all applications.
•
4 MB-2 GB - Win32-based applications, where each has its own address space. This
memory is protected so that other programs cannot corrupt or otherwise hinder the appli-
cation.
•
0-640 KB - real-mode device drivers and TSRs.
4GB
Ring 0
components
3GB
Core system
components, shared
DLLs, Win16-
based applications
SHARED
2GB
Win32-based
applications
PRIVATE
4MB
640KB
Real-mode device
drivers and TSRs
Figure H.9
System memory usage
H.7.3 GDI
The graphical device interface (GDI) is the graphical system that:
•
Manages information that appears on the screen.
•
Draws graphic primitives and manipulates bitmaps.
•
Interacts with device-independent graphics drivers, such as display and printer drivers.
The graphics subsystem provides input and output graphics support. Windows uses a 32-bit
