OS Fundamentals
Start Up
Windows 9x Start Up Process
1)
The ROM BIOS Bootstrap Process
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Power On Self-Test (POST) occurs
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The master boot record and partition table are read
2)
The Master Boot Record and Boot Sector
The
master boot record determines the location of the boot partition by
reading the partition table located at the end of the master boot
record. Once the location of the boot partition is determined, the
master boot record passes control to the boot sector in that
partition. The boot sector contains the disk boot program and a
table of disk characteristics. The boot sector checks the BIOS
Parameter Block (BPB) to find the location of the root directory,
and then copies the Io.sys file from the root directory into memory.
3)
The Io.sys File
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A minimal file allocation table (FAT) file system is loaded
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The MSDOS.SYS file is read
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The Starting Windows message is displayed
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The Logo.sys file is loaded and displays a startup image on the
screen
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If the Drvspace.ini or Dblspace.ini file exists, the
Drvspace.bin or Dblspace.bin file is loaded into memory
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The Io.sys file opens the System.dat file
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The Dblbuff.sys file is loaded if the "DoubleBuffer=1" is in the
Msdos.sys file
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If you have multiple hardware profiles , the hardware profile
you chose is loaded from the registry
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The Io.sys file processes the Config.sys file
4)
Real-Mode Configuration
Some
hardware devices and programs require that drivers or files be
loaded in real-mode in order for them to work properly. To ensure
backwards compatibility with these types of hardware devices or
programs, Windows 95 processes the Config.sys and Autoexec.bat files
if they exist.
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The Config.sys file loads drivers into memory. If the Config.sys
file does not exist, the Io.sys file loads the following
required drivers Ifshlp.sys, Himem.sys, and Setver.exe
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Windows reserves all global upper memory blocks (UMBs) for
Windows 9x operating system use or for expanded memory support
(EMS).
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The Autoexec.bat file loads files and terminate and stay
resident (TSR) programs into memory
The
Win.com File and the Windows 95 Environment
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After the Autoexec.bat file is processed, the Win.com file is
run
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The Win.com file accesses the Vmm32.vxd file. If there is enough
available RAM, the Vmm32.vxd file loads into memory, otherwise,
it is accessed from the hard disk. This may result in a slower
startup time. The Vmm32.vxd file is similar to the Win386.exe
file used in earlier versions of Windows
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The real-mode virtual device driver loader checks for duplicate
virtual device drivers (VxDs) in the Windows\System\Vmm32 folder
and the Vmm32.vxd file. If a VxD exists in both the
Windows\System\Vmm32 folder and the Vmm32.vxd file, the
duplicate VxD is "marked" in the Vmm32.vxd file so that it is
not loaded.
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The real-mode virtual device driver loader checks that all
required VxDs loaded successfully. If not, it attempts to load
the drivers again
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Once the real-mode virtual device driver loading is logged,
driver initialization occurs. If there are any VxDs that require
real-mode initialization, they begin their process in real-mode.
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Vmm32 switches the computer's processor from real-mode to
protected- mode
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After all the static VxDs are loaded, the Krnl32.dll, Gdi.exe,
User.exe, and Explorer.exe (the default Windows 95 shell) files
are loaded
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