Re: bootsect.bak
- From: "R. C. White" <rc@xxxxxxxxxxxxx>
- Date: Tue, 24 Nov 2009 17:24:47 -0600
Hi, Mikoyan.
The exact function of this file has changed with successive generations of Windows, so this answer may not be correct for all versions. (Also, I am not a techie, so, even if my explanation is correct, there probably are others who can explain it better than I can.)
When the computer is first powered on, it knows nothing. But there is an EEPROM (Electrically Erasable Programmable Read Only Memory) chip on the motherboard that holds the Basic Input/Output System (BIOS). These are the most basic, most primitive instructions that make the system start to "pull itself up by its bootstraps" - that is, to "boot" itself by starting from zero. These first instructions can't do much but tell the hardware to find the first internal hard disk drive, transfer the contents of the first physical sector on that disk into memory, and then start executing the instructions found there. This first sector on each HDD is the MBR - the Master Boot Record. A sector is only 512 bytes long; there is just enough room to hold the 64-byte Partition Table plus about 400 bytes of still-primitive instructions. The Partition Table has room for four 16-byte entries; each of these tells where one partition starts and ends, plus a few bits of information about that partition, including whether it is the one Active (bootable) partition on that HDD. The MBR code finds the start of that Active partition and loads the first physical sector of that partition into RAM and starts executing those instructions. This first physical sector of the Active partition is the "boot sector". This partition is the "System Volume" for this boot session; it is often referred to as the "System Partition" since it must be a primary partition, not a logical drive in an extended partition.
The contents of the boot sector vary, depending on which operating system wrote it onto the hard drive. The Win9x boot sector had instructions to look for the files IO.SYS and MS-DOS.SYS. Win2K/XP boot sectors are based on Windows NT, so they look for NTLDR, the NT loader. Vista and Windows 7 boot sectors look for bootmgr, the boot manager.
No matter which code is in the boot sector, it must find a file with no extension in the Root of that Active partition. At this very early boot stage, the computer doesn't yet know how to deal with extensions or folders or multiple partitions, much less multiple hard drives. So those first startup files must be in the Root of that partition and the correct boot sector code must be on the first physical sector. This sector is OUTSIDE the file system, so it can't be copied or backed up or otherwise handled by normal Windows programs or utilities. Only special system-level utilities, such as Windows Setup, can deal with the boot sector.
When we install WinXP, Setup writes the XP-style boot sector code, which will look for NTLDR - which will then find the files NTDETECT.COM and Boot.ini, also in the root of the System Partition, and use those to find the file ntoskrnl.exe in the Boot Folder (typically C:\Windows - but not necessarily) to load WinXP.
But Vista and Win7 write different code into the boot sector. This looks for the file "bootmgr" - no extension - in the Root of the System Partition. Bootmgr reads the files in the hidden \Boot folder on that partition; this folder holds the Boot Configuration Data (BCD) which Vista/Win7 uses to find the file winload.exe in the Boot Folder (also often - but not always - C:\Windows, the same filename as for WinXP) and use that to boot Vista or Win7.
When Vista/Win7 Setup discovers an existing WinXP boot sector in the System Partition, it saves a copy of that sector in a new file in the Root of the System Partition; this file is typically C:\bootsect.dos. This is a part of the process of updating the BCD to provide for a multi-boot system, which will present an operating system menu at each subsequent reboot.
Later, at each boot, if the user selects to boot Vista/Win7, bootsect.dos will be ignored, along with NTLDR, etc. But if the user chooses to boot an "Earlier version of Windows", then bootmgr will step back out of the way and load the WinXP-style boot code from bootsect.dos, which will find NTLDR, etc., and load WinXP. After this initial selection, the computer will see only WinXP code or only Vista/Win7 code; neither will interfere with the other.
After all that, I still haven't mentioned bootsect.bak. I have both the ..dos and .bak versions of bootsect in my System Partition. Each is exactly 512 bytes, one sector, with no apparent differences. I'm not sure how .bak came to be created, but it is dated later than the .dos file.
Now, let's hope a true techie will fill in the missing links. ;<)
RC
--
R. C. White, CPA
San Marcos, TX
rc@xxxxxxxxxxxxx
Microsoft Windows MVP
Windows Live Mail 2009 (14.0.8089.0726) in Win7 Ultimate x64
"Mikoyan" <Mikoyan@xxxxxxxxxxx> wrote in message news:eLBlkVUbKHA.1592@xxxxxxxxxxxxxxxxxxxxxxx
Can anyone tell me what bootsect.bak does?
.
- Follow-Ups:
- Re: bootsect.bak
- From: Massaro. Antonio M
- Re: bootsect.bak
- References:
- bootsect.bak
- From: Mikoyan
- bootsect.bak
- Prev by Date: Re: Windows 7 NG's ?
- Next by Date: Re: Newsgroups ?
- Previous by thread: Re: bootsect.bak
- Next by thread: Re: bootsect.bak
- Index(es):
Relevant Pages
|
