[pchelpers] FW: Information

-----Original Message-----

Technology tips 

Unbootable Systems

by John L. Joseph, Diskeeper Development Section, Executive Software
International

Occasionally, we'll get a call in Tech Support where the user says "my
system won't boot." When further information is requested, the user
tells us that he's got a message on the screen that looks like this:
Windows NT could not start because the following file is missing or
corrupt: <Winnt_root>\System32\Ntoskrnl.exe. Please re-install a copy of
the above file.

 <http://www.diskalert.com/diskalert/diskalert.asp?ad=esil10> The
manager of Tech Support asked me about this situation, so I asked our
Tech Support guys to find an example of a disk experiencing this problem
so I could "look at it under the microscope."

As you could expect, it was not easy to get our hands on such a disk.
Usually, when a user sees this, it's Saturday at midnight, so he just
reinstalls Windows and then tells us about it on Monday. Or the disk is
in a production system or laptop and can't be pulled. Finally, however,
someone sent a disk in exhibiting this problem. (He got it back 48 hours
later.)

When I put it "under the microscope," I was amazed. The stated file was
NOT missing. The file was right there on the disk and could be examined
easily with any number of tools, including Explorer, Command Prompt type
command, hex editor, etc. The stated file was NOT corrupt. The file
correctly compared, byte-for-byte, with the same file from another
system running the same operating system.

Yet, the system would not boot!

So I did what the error message told me ... (the obvious thing): I
deleted the file and copied in a replacement file of the same name into
the same directory.

Upon reboot, the following message appeared:

Windows NT could not start because the following file is missing or
corrupt: 
\WINNT\SYSTEM32\CONFIG\SYSTEM\
Please re-install a copy of the above file.

Again, when I looked on the disk, the directory specified was neither
missing, nor corrupt. All the expected files in that directory were
visible, so the directory wasn't "corrupt."

So I decided to dive into the Microsoft Knowledge Base and see what was
up.
Sure enough, there are dozens of articles about files being "missing or
corrupt" during bootup. 

So what was the problem?

The problem was that some key files needed for booting the operating
system were beyond cylinder 1023 on this volume. The C: drive was 25 GB
big! But, given the CHS (cylinder/head/sector) setup on his machine, the
boot sequence could only see the first 7.68 GB of the volume during the
initial boot phase. 

So the file was neither missing nor corrupt. It was simply beyond where
the INT 13 BIOS interface could find it. And when I deleted the first
file and replaced it, it fell within the first 7.68 GB. 

This is very important! The stated file was NEITHER MISSING, NOR
CORRUPT. It was still there! It was just unreachable! Booting from CD,
the system came right up. I was able to run the system just fine.

When I returned the disk to the user, I gave him a write-up of what I'd
discovered. His immediate response was, "Then why did <vendor> send me
an operating system installed this way?!?!?" To which I of course
responded, "Don't ask me, ask <vendor>." (It could be any vendor who
sends out boot partitions larger than 1023 cylinders.)

The bottom line is that it continues to be hazardous to install even
Windows XP on a system partition that extends past the 1023 cylinder
boundary on a disk. 

The applicable Knowledge Base article continues to be:

Q224526 Windows NT 4.0 Supports Maximum of 7.8-GB System Partition 

even though you may be running Windows XP. Because the limitation is in
the BIOS, there's very little can be done about it.

The difficulty I have run into recently is that another article:

http://www.microsoft.com/hwdev/tech/storage/ntfs-preinstall.asp, which
steers system managers into making the C: drive arbitrarily large under
Windows XP. I'm afraid that my experience continues to indicate that
keeping any bootable Windows partition wholly contained within the
1023-cylinder limit on the boot drive is the smartest thing to do.

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