Re: Linux syscalls

From: Beth (BethStone21_at_hotmail.NOSPICEDHAM.com)
Date: 06/09/04

  • Next message: rjb: "Re: Locked memory" 
    Date: Wed, 9 Jun 2004 00:41:05 +0100

    Arargh wrote:
    > ntldr (NT4 version) makes NO Int 21h calls. It also enters
    protected
    > mode, which is unlikely for a DOS program. It is a mixed-mode
    16bit
    > real and 32bit protected program from what a quick look tells
    me.
    >
    > IMO, a stand alone program.

    In fact, that sounds like the _perfect description_ of an "OS
    loader" program...

    A raw binary file that doesn't access any OS routines (because,
    being the OS loader, it runs _prior_ to the OS existing - hence
    can't access any OS, obviously - so can only use BIOS and direct
    access)...and then is "mixed 16 / 32 bit code" for making that
    "protected mode switch" from the real mode that the PC naturally
    boots into to 32-bit protected mode that the NT kernel runs
    under...plus, the mnemonical name "NTLDR" is also strongly
    backing this up as most likely standing for: "NT's LOADER"...

    Basically, "NTLDR" is NT's actual OS loader binary file that the
    bootsector loads and transfers control to (after all, a
    bootsector can only be 512 bytes so it can't do the whole
    process for any non-trivial OS in such a small space...well,
    instead, it can load a second file from disk to actually do the
    real OS loading process...a "loader" program..."IO.SYS" used to
    do this with DOS, "NTLDR" does it with NT :)..."BOOT.INI" is, as
    can be seen with Notepad, the actual plain text file with ".ini"
    configuration text for the list of OSes under the "bootmenu" (a
    menu by-passed if there's only one OS installed but a website I
    read suggested that this is one of "NTLDR"'s jobs in printing
    out the "bootmenu" as well as then actually proceeding to load
    the OSes selected from the menu)...

    "NTDETECT.COM" does play a part in this somewhere but I don't
    know exactly what...

    The other files there, though, are, in most cases, basically
    "backwards compatibility"...the "0 bytes" file size being a clue
    that they _can't_ be doing anything because, really, they aren't
    even files...they are more like "placeholder filenames"...just
    directory entries without any actual data file attached...

    Beth :)

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