This is news to me. Care to expand on this? Windows Server 2003 products may use a boot loader file named "Osloader.ntd" (NTLDR and NTDETECT.COM may still exist). I am uncertain between the relationship between the different boot loaders of Windows Server 2003. Well, Osloader.ntd is ONLY used when booting from ADS: http://support.microsoft.com/kb/843536/en-us Probably just like SETUPLDR.EX_ is used instead of SETUPLDR.BIN for PXE/RIS installs/PE's. Close. In fact, you should compare it with OSLOADER.EXE, which is (as Jaclaz already knows is the second part of NTLDR (the first one being the StartUp module which brings the computer into 32-bit mode). So if you compare them, you'll find they are extremely similar, they even have the same .PDB referenced; the only differences are in the PE header: there is a supplementary section, named .detect the ImageSize is bigger the checksum are different (better have to, since they are checked ) Now, if you consider the extra baggage at the end of OSLOADER.NTD, it is around 46 KB, and it is... NTDETECT.COM So I believe it works this way: PXE ROM, STARTROM.xxx sent with TFTP, asks for "NTLDR" but expects a .EXE (this is standard behaviour of Microsoft's PXE infrastructure), the server sends this OSLOADER.NTD packaged as a single file and the OsLoader works alone, without need to download a further NTDETECT.COM later. What I do not understand yet is how OsLoader does to "know" it should either load_from_disk/ask_via_tftp for NTDETECT.COM (normal case), or just have a look in memory behind itself (osloader.ntd case). The evident way to do it (just inspect the COFF header) is not that evident, since I did not see any reference to ".detect" in the binary; perhaps it does that by direct inspection to entry #12, without checking the name? OK, next stage is to build some frankenboot, i.e. paste StartUp and OsLoader.ntd as NTLDR, removing NTDETECT.COM and see if it works... Another try is to "append" ntdetect.com to setupldr.bin (or renamed version of it, like cmldr ) and see if Setup is able to boot without needing the ntdetect.com extra baggage... PS: I am a newbie here, so if this should be redirected to another thread (or a new one), please do; also I'd appreciate pointers to similar researches already done about OsLoader.NTD.