670 Computer Service and Repair
The
io.sys
file then processes the config.sys, command.com,
autoexec.bat
and
win.com
files. The Windows startup process only loads the
config.sys
file and
then the
autoexec.bat
file, if they are required for support of legacy programs.
With these operating systems, Microsoft started moving away from the use of
config.sys, autoexec.bat, and the
win.ini
and
system.ini
files. The
win.ini
and
system.
ini
files were used with earlier versions of Windows and stored hardware and
software information. These files were replaced with the system registry. The
system registry is a database that stores information about the hardware and
software systems. The registry is continually referenced by the operating system
and software programs. The autoexec.bat, config.sys, command.com, and
io.sys
have been renamed for Windows 98 by changing the file extensions to .dos. For
example,
io.sys
in Windows 98 is now called io.dos.
The config.sys and autoexec.bat files are not required for
Windows 95, 98, and Me but are still available to maintain
downward compatibility with legacy software programs and
drivers.
After
autoexec.bat
loads, the
win.com
file loads.
Win.com
then loads the
Windows kernel (krnl386.exe), the graphic device interface (gdi.exe), and user.exe.
The
krnl386.exe
is the kernel file or core program of the operating system. (There
is also a krnl286.exe, which was used with earlier models of the operating system.)
It manages the processor functions and system resources such as memory DMA
channels, IRQs, and port functions. It also loads programs, schedules processor
events, and controls the actions of the CPU. The
user.exe
file is designed to
allow the user to manipulate the icons, windows, and elements that make up
the user interface. The
gdi.exe
is the graphic device interface. It is responsible
for displaying the screen images used as the interface between the user and the
operating system. All three files are located in the directory structure under
Windows |
System.
After these three program files are processed, the logon window appears. The
user logs on, and the system processes the user’s individual settings.
The system registry contains two main files called
system.dat
and user.dat.
The
system.dat
file contains information that is specific about the computer. The
user.dat
contains information about the user. A PC may have multiple users, thus
there can be multiple
user.dat
files containing information about each specific
user. Such user information would include, but not be limited to, desktop layout
preferences and specific documents created by the user.
Windows 2000 and XP Boot Sequence
Windows 2000 and Windows XP are designed on the NT operating system
kernel, not the traditional Windows 95/98 operating system kernel. However,
their outward appearance is remarkably similar.
As with the other systems covered so far, these systems start with the POST,
load the BIOS program, and look for the boot sector as well as the MBR. Then,
Windows 2000 and XP follow the NT system. Once the BIOS has loaded the
ntldr
file into RAM, it turns control over to it for the boot loader phase. During
this phase,
ntldr
loads the program startup files from the boot sector. Part of
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