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Windows Vista PreOS Environment: What happens before the OS loads

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Description

What happens, exactly, when you turn your computer on? Yeah, you see the black screen and words scroll by, then, finally, the Vista startup sound... But, there's a good deal of code that runs in this preOS environment, much of it composed in languages you've probably never written (like 16-Bit Real Mode code). What does the BIOS do, anyway? Why do we need a BIOS? Vista can run without a BIOS: It supports UEFI. What's UEFI, anyway?

This is a rare interview with some of the developers nobody sees during the day (Smiley), who live and breathe in the preOS space (this is the single threaded world of pre-operating system start-up context where there is no memory manager, no object manager, no kernel period - it takes highly skilled developers to write code in this memory confined space, the land of real mode code and the BIOS).

Meet Jamie Schwartz, Development Lead, Windows Kernel Dev team, and Andrew Ritz, Development Manager, Windows Kernel Dev team. They tell us all about the wonderful world of preOS. Enjoy.

Tags:

Kernel, Operating System, OS, Windows Vista

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The Discussion

  • User profile image
    littleguru
    Thanks for this vid... I'm going to enjoy it.
  • User profile image
    ZippyV
    littleguru wrote:
    I'm going to enjoy it.
    Weird fetish you have. Tongue Out

    Got a couple of questions:
    - Why do we have to create a dos floppy to flash a bios?
    - Is EFI now supported or not in Vista?
    - Are there any motherboard manufacturers that are going to ditch the bios and put EFI on it?
    - Can I boot to Linux using the Vista bootloader (without using a Linux bootloader)?
  • User profile image
    bitdisaster
    ZippyV wrote:
    
    - Can I boot to Linux using the Vista bootloader (without using a Linux bootloader)?


    XP bootloader can also boot a linux. You have to create an image of the linux bootsector. This image file can be loaded by the xp bootloader as well as by the vista bootloader
  • User profile image
    PerfectPhase
    ZippyV wrote:
    
    - Why do we have to create a dos floppy to flash a bios?


    I haven't had to do that for a long time, all my machines (Dell) support flashing from within windows.

  • User profile image
    littleguru
    ZippyV wrote:
    
    littleguru wrote: I'm going to enjoy it.
    Weird fetish you have.


    Tongue Out
  • User profile image
    RichardRudek
    So does this mean we are going to get a WinRE video ?

    Like with my skillset, I'm seriously considering wether there's any opportunity for someone like me, creating "addons" to WinRE, or perhaps convincing them into allowing some kind of addon API.




    Now a direct question for Jamie/Andrew.

    I ran into an issue a couple of days ago which I thought had been fixed since Windows 2000 sp2. That is 48-bit LBA on ATA (IDE) Hard disks.

    In this case, there was an existing Windows 2000 Server where the Admin needed to setup a parrallel install of Windows on a second D: volume. Now this was a 250MB basic disk volume, and was ~60-70% full. The Admin booted off his Windows 2000 sp4 CD (slip-streamed) and proceeded to through the text-mode setup, installing to D:\WINNT. Upon reboot, entering what should be the 2nd stage, GUI part of the installer, you get a BSOD and a message about D:\WINNT\SYSTEM32\NTOSKRNL.EXE being missing.

    Upon my investigation, it became apparent that NTOSKRNL.EXE was well beyond the old 28-bit LBA limitation (~128GB point). But I wasn't able to investigate any further, due to urgency. Is this likely an issue of a bad service pack integration of the Windows 2000 Server CD. That is, the CD was still using the old, pre 48-bit LBA IDE/ATAPI driver(s) ?

    PS: I side-stepped the issue by resizing and moving the partition up, leaving a 2GB partition at the start of the disk for the new parallel install.

  • User profile image
    liridon shala

    Interesting video I'm enjoying it, and what is amazing me is that is running without bios hmm kind of suprised.

     

    Great job definitivly !

  • User profile image
    AJenbo
    Thank you for this video i was dreaming of it this weeks end and here it is Big Smile

    Just a few notes here.

    Vista does NOT run on PowerPc, Mac have switched from PowerPc to x86 and that is why it can run on them.
    Some early edition of Windows NT worked with PowerPc but it was never releasted to the public i belive.
    ZippyV wrote: 
    Got a couple of questions:
    - Why do we have to create a dos floppy to flash a bios?
    - Is EFI now supported or not in Vista?
    - Are there any motherboard manufacturers that are going to ditch the bios and put EFI on it?
    - Can I boot to Linux using the Vista bootloader (without using a Linux bootloader)?


    Yes Vista supports loading from EFI.
    Yes the bios is beeing ditched VIA and other chip manufacture are working on EFI's to go into pc motherboards as we speek (type).

    The grate thing about EFI is that you can have it use hardware better alowing to run the hardrive at full speed on boot up, but sound like the Vista bios bootloader partialy is cabable of this.
  • User profile image
    univert
    It seems many a lot of guys at microsoft are left handed.
    I have seen serveral of them on channel 9.
    A very interesting phenomenon.
  • User profile image
    AJenbo

    Why else would it bee knee dep in html and offers of cheap goods.

  • User profile image
    mbluett
    I would think that most mainboard vendor's will take the hybrid (EFI - BIOS) approach as they can't be sure the person who purchases their MB will have the necessity to boot Linux (or some other OS) along with Vista.

    I would guess this because I am assuming a strictly EFI approach (at least currently) will not allow Linux to boot. Is this assumption correct?
  • User profile image
    AJenbo
    EFI can emulate bios, but i expect linux will be catching up with EFI if they havent already.
  • User profile image
    Penfold
    Smiley Really Cool vid.. been waiting for something like this for Vista.

    I have a question for Jamie and Andrew..

    We have a product that has its own boot code, which pre authenticates the user before allowing boot. Is possible to hook in some form of authentication into the boot loader, other than from a keyboard menu item at the pre boot time, say from a USB device or user name and password or other devices, X509 Certificates ? etc.. this would really help our development onto vista? without having to use bespoke boot code?

    Thanks
  • User profile image
    Dodo
    That's great, finding this due to lots of crosslinks, but now I finally know how to do something I planned a long time ago...

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