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When you turn on your computer running Windows 95, this is what happens inside your little box of electronics:

  • BIOS Bootstrap
    Your computer goes through the POST (Power On Self Test) routine. This detects annoyances like bad memory, ports, video, CPU and basic devices. The system then identifies any Plug-and-Play devices, locates the bootable partition on the hard drive and begins the load of the Master Boot Record (MBR) and the partition table.
  • MBR Execution
    The root directory is identified and the IO.SYS is executed.
  • Real-Mode Boot
    MSDOS.SYS is checked for boot parameters. The silly Starting Windows 95 message is displayed, and the system waits for a function key to be pressed (for selection of boot process, etc). After the pause, the LOGO.SYS image is displayed. If DBLSPACE.INI is present, the DRVSPACE.BIN is loaded. The SYSTEM.DAT is checked for errors, then it it is loaded. If the SYSTEM.DAT is bad, the backup (SYSTEM.DA0) is loaded instead. If double-buffering is needed, the system loads it. Based on the detected hardware, a hardware profile is loaded. At this point, IO.SYS reads and executes the CONFIG.SYS and AUTOEXEC.BAT files.
  • Real-Mode Configuration
    If there is no CONFIG.SYS, Windows loads the HIMEM.SYS, the IFSHLP.SYS and SETVER.EXE and other environmental controls. The CONFIG.SYS is not required, but some older programs that depend on DOS may need it.
  • Protected-Mode Boot
    WIN.COM is executed. This causes VMM32.VXD and other virtual drivers noted in the registry and SYSTEM.INI file to be loaded. The processor is switched over into protected mode and the virtual device drivers are initialized. The core Windows kernel is loaded, along with the GDI, user libraries and the Explorer shell. Network support is activated.
  • Programs
    Everything in the Startup group is loaded sequentially. If a program is referenced in the registry to RunOnce, the program is run and the key is deleted. An example of this is after you install Internet Explorer. After it is installed and you reboot, it loads up a default page and displays info to the user. Some other programs have a little checkbox to disable showing items on startup, such as tips for using Windows 95.

And that is it, Windows 95 is now ready to run (or crash). Enjoy!

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