Windows 9X Boot-up Sequence

IO.SYS: A hidden file in the root directory of the primary drive. This file is actually a small DOS core module. It starts the Windows 9X boot process and looks for MSDOS.SYS.

MSDOS.SYS: This is now a hidden ASCII text file on the root directory that contains information about the boot configuration. For more information on the configuration capabilities of MSDOS.SYS, click here.

DRVSPACE.BIN: This program checks the integrity of the information in SYSTEM.DAT (part of the Registry for Windows9X) and then loads it into memory. DRVSPACE.BIN is also a compression program and if a DRVSPACE.INI file is present in the root directory, it allows for disk compression capability.

SYSTEM.DAT: Part of the Registry, this file provides information about the setup of the system, the different names of the devices, where they are located and the location of the drivers to operate them. It contains computer and software settings. It is similar to the SYSTEM.INI file.

USER.DAT: The other half of the Registry. This file contains user-specific information such as screen colors, icon choices, application access, etc...
It is similar to the WIN.INI file.

CONFIG.SYS: A user-configurable text file that usually contains device drivers and system setup values. This file is not necessarily needed, but if there are legacy (non-Win9X) devices, this is where they can be loaded.

AUTOEXEC.BAT: Another user-configurable text file that is used to set system variables and load TSRs and some utilities. AUTOEXEC.BAT is also not a necessary file for Win9X.

SYSTEM.INI: This file contains information about your computer's hardware settings. It must be in the Windows folder for Windows to start. It is used to load various drivers including sound, video and mouse. It may also contain some 16-bit drivers for installed hardware that doesn't use 32-bit drivers.

VMM32.VXD: The virtual machine manager runs after AUTOEXEC.BAT, loading other virtual device drivers it finds in the Registry and SYSTEM.INI. WIN.COM then switches from Real Mode to Protected Mode, initializing the different devices and loading the following files.

KERNAL32.DLL: Contains most the Operating System for Windows9X.

GDI.EXE/GDI32.EXE: These files are the graphics engines for both 16-bit and 32-bit graphics displays.

USER.EXE/USER32.DLL: These files provide the User Interface and control the input information.

WIN.INI: Contains application information configuration.

STARTUP Group: This is the STARTUP folder and contains any application programs that you may want to run everytime Windows9X starts.