Error loading OS: FAT32-LBA problem or something else?

[Gerard Oberle]

I have a PC about five years old, unfortunately, still my primary PC used for paying bills, some work related stuff, and other things that preclude simply trashing the working installation of XP in the first primary partition, or doing other "risky" things with it.
 
After "installing" FreeDOS on a FAT-32 partition, I attempted to boot it in a couple of ways, each of which resulted in the message:
 
   Error loading OS
 
immediately after all the BIOS blather.  <Ctrl/Alt/Del> worked to start the boot sequence again (fortunately).
 
The machine is an unbranded computer having an ASUS KM 400 series motherboard, an AMD Athlon 2800 (2.0 GHz processor), 1 Gb RAM and a Western Digital "160 Gb" disk, in the typical marketing way of using powers of ten, not two, so it really has about 149 Gb.
 
XP is installed on the first primary partition, NTFS, which has 37.38 Gb according to the disk manager.  (It always had been so - I anticipated playing with other operating systems, and left room.  I didn't repartition NTFS, etc.  I'd had an older RedHat disto on the rest, but I saved the stuff I wanted and blew it away.  I offer this info only to demonstrate that Grub had been capable of booting something beyond where XP was installed.)
 
mbrfix (an open source program for NT/XP/etc.) reported cylinders 19457, tracks 25, cyl 64; first partition 38279 Mb type 7 (NTFS), second 894 Mb type 12 (FAT32-LBA).
 
I'd created the FAT-32 partition from XP using the disk manager.  XP saw it as drive F:, FAT-32.  GParted from Puppy Linux (my favorite "live CD" distro of the week) likewise saw it the same way, with the LBA flag set.
 
I installed FreeDOS from the CD to what it thought was C: (okay).  XP likewise saw all the FreeDOS stuff thus written into that partition.
 
I made the FreeDOS partition active from XP, and tried rebooting.  This generated the error message above.  I also tried booting from a standalone Grub CD I'd had lying around, using rootnoverify (hd0,1); chainloader +1; boot; with the same result.
 
Speculating the perhaps the installation hadn't installed a partition boot sector to the FAT-32 partition, I rebooted the FreeDOS CD, went to the C: drive, and issued the command
 
sys C:
 
which reported sectors/trk: 63, heads: 255 hidden: 78397200
FAT starts at 4AC3F10 + 26 (78397200 + 38)
Boot sector load seg ... 60h
 
The word "hidden" next to the number that curiously matches where "FAT starts" has me suspicious, for some reason. :-)
 
I found a prior article on the mailing list in which someone reported, around 2007, that FreeDOS had problems with FAT32, sometimes mistaking FAT32-LBA for FAT32-CHS, or something to that effect.  The author indicated that there exists a Perl script (!!!) to fix this.
 
Does anyone have insight into this?  Is it the 1024 cylinder problem?  Is there a practical workaround besides using FAT16 (kind of ugly for an almost 1 Gb partition)?  If running a Perl script it the answer (yikes!), where is it, and under what environment does one execute it.  (Is Perl installed with FreeDOS?  Or would I use Cygwin Perl under XP?  The latter seems doubtful to me, since using Perl to tamper with boot sectors seems like the kind of thing that can't easily be done.  I'm not afraid of Perl - I use it all the time on Unix, but not for this sort of thing.)
 
Sorry for the long message.  I'm never sure how much detail to include.  I know that too little is pointless, since nobody can help if they don't have the facts.
 
 
Thanks in advance.
- Jerry Oberle
 
perl -e 'printf "%cailto%cgoberle%chot%scom\r\n", 109, 58, 64, "mail."'
     
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[Eric Auer-3]

Hi!

> After "installing" FreeDOS on a FAT-32 partition, I attempted to boot
> it in a couple of ways, each of which resulted in the message:
>
> Error loading OS

Maybe your FAT partition is not marked active or you did not SYS it?

> mbrfix (an open source program for NT/XP/etc.) reported cylinders
> 19457, tracks 25, cyl 64; first partition 38279 Mb type 7 (NTFS),
> second 894 Mb type 12 (FAT32-LBA).

Sounds okay...

> sys C:
>
> which reported sectors/trk: 63, heads: 255 hidden: 78397200 FAT
> starts at 4AC3F10 + 26 (78397200 + 38) Boot sector load seg ... 60h

The hidden means that the partition starts after 78397200
sectors (of 512 bytes each) of something else. A better
name would probably be partition offset but the field in
the data structure apparently is even older than the idea
of having multiple partitions, so originally it was used
to reserve hidden space before the start of a FAT disk...

SYS may have accidentally made a CHS boot sector while you
needed LBA. You could try using another / newer version of
our SYS. Other people on this list will probably suggest
some :-). In Linux, you can also use sys-freedos-linux, in
particular the "sys-freedos.pl" perl script. You need to
install nasm first to run this :-). The script basically
calls NASM to compile a DOS boot sector and then updates
some values in the boot sector to match your partition.

Make sure that you run it only on a FAT partition, not
on other partitions and not on whole disks!

> Does anyone have insight into this?  Is it the 1024 cylinder problem?

Only if SYS happened to select a CHS boot sector for you.
You need a LBA boot sector here...

> it.  (Is Perl installed with FreeDOS?

Yes but the script is for Linux ;-)

> Or would I use Cygwin Perl under XP?

There are other tools for XP I guess...

Eric

PS: Please mail me off-list if you need help for using sys-freedos.pl



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[Christian Masloch]

Hi Jerry,

> After "installing" FreeDOS on a FAT-32 partition, I attempted to boot it  
> in a couple of ways, each of which resulted in the message:
>   Error loading OS
> immediately after all the BIOS blather.

This message possibly isn't displayed by FreeDOS boot code. I think  
neither FreeDOS's MBR, boot sector or kernel contain this message. Thus  
I'd assume it's from the Windows MBR. (I'm using a localized Windows so I  
can't compare it to the message of its MBR.)

> a Western Digital "160 Gb" disk, in the typical marketing way of using
> powers of ten, not two, so it really has about 149 Gb.

Use binary prefixes then.

> I offer this info only to demonstrate that Grub had been capable of  
> booting something beyond where XP was installed.)

> I'd created the FAT-32 partition from XP using the disk manager.

Then you might have created a logical partition. You might not be familiar  
with the difference between logical and primary partitions. However, the  
default Windows and FreeDOS MBRs don't support booting from logical  
partitions (GRUB does), and that's most of the difference anyway. Even  
with GRUB, the FreeDOS kernel might not work when booted from a logical  
partition. Ask the kernel developers about that.

GParted should display whether your FAT32 partition is a primary or a  
logical one. (Logical partitions are contained within extended  
partitions.) If you recreate the FAT32 partition with GParted, it should  
also allow you to select whether it should be logical or primary.

(Personally, I'd prefer GParted over the Windows disk manager for most  
partitioning-related work anyway.)

> I made the FreeDOS partition active from XP, and tried rebooting.  This  
> generated the error message above.

That Windows allowed you to make the partition active is strange. If it  
really is a logical partition, it shouldn't allow you to do that. If my  
assumption is wrong and the partition is a primary one, everything should  
work fine for you.

> Speculating the perhaps the installation hadn't installed a partition  
> boot sector to the FAT-32 partition, I rebooted the FreeDOS CD, went to  
> the C: drive, and issued the command
> sys C:
> which reported sectors/trk: 63, heads: 255 hidden: 78397200
> FAT starts at 4AC3F10 + 26 (78397200 + 38)
> Boot sector load seg ... 60h
> The word "hidden" next to the number that curiously matches where "FAT  
> starts" has me suspicious, for some reason. :-)

"Hidden sectors" is the usual term for "sectors in front of this  
partition", and was just abbreviated to "hidden" here. "FAT starts" means  
the first FAT's first sector, which of course is inside the partition.  
It's somewhat useless, but this message from SYS always displays the same  
number twice. Anyway the "hidden" number doesn't mean the partition itself  
is hidden at all (although I understand your suspicion).

> I found a prior article on the mailing list in which someone reported,  
> around 2007, that FreeDOS had problems with FAT32, sometimes mistaking  
> FAT32-LBA for FAT32-CHS, or something to that effect.

It might be caused by this. You can update your SYS program with a version  
 from kernel 2039 first, that could fix the problem already. This version  
of SYS also allows you to overwrite SYS's broken auto-detection (the only  
actual problem) using the option "/FORCE:LBA" (which isn't documented for  
some reason).

> The author indicated that there exists a Perl script (!!!) to fix this.

Sounds adventurous. That might have refered to the Linux script which was  
written so a boot sector could be written to a DOS partition from Linux.  
This however is a SYS replacement, not a fix for the broken SYS. It won't  
help you if an updated SYS doesn't.

> Does anyone have insight into this?  Is it the 1024 cylinder problem?

If anything with cylinders is involved, SYS would have installed the CHS  
boot code (which can't work for your partition). With LBA, the boot code  
and kernel and operating system don't have to care about cylinders or  
heads or tracks at all.

> Is there a practical workaround besides using FAT16 (kind of ugly for an  
> almost 1 Gb partition)?

FAT16 possibly wouldn't help either. And I'd use it only for partitions up  
to 512 MiB anyway, anything larger than that is inefficient.

> Sorry for the long message.  I'm never sure how much detail to include.
> I know that too little is pointless, since nobody can help if they don't
> have the facts.

That's right. So writing a long mail is indeed better. You don't have to  
apologize for that, even if we don't need all information you sent.

Regards,
Christian

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