not good news.
when a drive this old starts to fail, even if you fix it this time the chances are is going to fail again shortly.
Time to install a CF.

By the way, what's the brand of the hard Drive ?

Rudi_K wrote on 2021-08-11, 09:55:

Hello, […]
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Hello,

I have a issue with my good old 486 DOS PC.
When copy some files to the Harddrive it fales halfway through copying the files.
then After a Reboot it won't boot from my harddrive any more (A 814 MB IDE drive)
The bios still sees the drive, I can hear it spin up, but error (No OS found)

Then I boot with bootdisk, and Fdisk still sees the partion.
But wen I enter c:\ the error is "Invalid media type"
Scandisk c:\ give the Notification "Scandisk kan station C niet controleren" (Dutch OS) which means cannot check the C drive

Are there some tools I can use to fix the drive. (It should be nice to keep the data, the last backup is from a year ago 😀
thank you in advance.

Best Regards,

Rudi Korterink.

Many 486 mainboard BIOSes (which contain the harddrive support) do not support drives above 504MB. Possibly trying to write past the 504MB point of the drive overwrites data at earlier parts of the drive. In the current case, it sounds like at least the boot sector is gone. If you are lucky, at least one of the FAT copies is still intact. I used to recover from damage like by hand that using software like NU when I was young, but I'm confident there is data recovery software out there (you might try to take a shot at photorec which is/was recommended on camera CF or SD cards with corrupted management data) that could try to save a lot of stuff from that drive.

Another cause for your current issue might be broken RAM, so the computer started to mix up stuff while you copied the data and accidentally overwrote the boot sector of the partition. For processors like the 486DX2/66, which get quite warm, a failed processor fan might also cause misbehaviour that finally results in filesystem corruption.

As you describe the symptoms at the moment, it doesn't sound like the drive is physically damaged, which is a good starting point.

If the issue is indeed because of a 504mb limit, after hopefully recovering the data, I'd recommend installing EZ-Drive. I use it on my 486 and it lets me use the full capacity of an 8GB (DOS 6.22 FAT16) and even a 40GB HDD (Win9x FAT32) with no issues.

Here's a bootable install floppy of it if you're curious:
https://mega.nz/file/mxN2yBqB#-TnIZvv388_0JVu … jYFX5VSBaOZVmkU

A useful thing is also Ultimate Boot Disc, where You will find among other things a number of tools to diagnose HDD: https://www.ultimatebootcd.com/

Ah ok, hopefull the drive is not broken 😀
I will try EZ-Drive.
But the bios of my PC (its a mobo with PCI and ISA) recognized the drive after set it up as 814MB.
But there was someware around 350MB free space, so it could be the 504 issue, but I think thats strange that i'm able to select the 814 MB size.
(PS its a Caviar 2850) (cyl 1654, Heads 16, Precomp 65535 landzone 1023 sectors 63 and mode Normal)

I think the bios indeed only reconice the 540 limite size, see screenshot below from the EZ-drive.
Can I use the EZ-drive to modify the bios ?
no experience with it 😀

Rudi_K wrote on 2021-08-11, 11:57:

But there was someware around 350MB free space, so it could be the 504 issue, but I think thats strange that i'm able to select the 814 MB size.
(PS its a Caviar 2850) (cyl 1654, Heads 16, Precomp 65535 landzone 1023 sectors 63 and mode Normal)

Mode normal, 1654 cylinders is not going to work. In that mode, the C/H/S values passed by DOS to the BIOS will be sent 1:1 to the IDE drive.

The classic BIOS functions that read and write from the hard drive only accept cylinder numbers from 0 to 1023, although IDE drives support cylinder numbers up to 65535. On the other hand, IDE drives only support head numbers 0-15, whereas the interface between BIOS and DOS supports head numbers 0-255. If your BIOS is set to "mode large" (assuming it supports it), it would talk to the drive with 1654 cylinders, 16 heads and 63 sectors, but talk to DOS about 827 cylinders, 32 heads and 63 sectors. So two "IDE cylinders" are combined to form one "DOS cylinder", to keep the cylinder count below 1024. As you explicitly wrote "mode Normal", a translation like this does not happen on yout computer.

If you change the scheme from "normal" to "large", you need to re-partition and re-format the drive. That's an option for after data recovery.

Rudi_K wrote on 2021-08-11, 12:12:

I think the bios indeed only reconice the 540 limite size, see screenshot below from the EZ-drive.
Can I use the EZ-drive to modify the bios ?

Kind of yes. You can install EZ-drive to replace the IDE driver part of the BIOS. EZ-drive will get loaded into RAM by the classic BIOS functions early during the boot process, and DOS will automatically use the replacement BIOS functions in RAM provided by EZ-drive.

On the other hand, if your BIOS supports "mode large" and/or "mode LBA", you can just enable that feature in your BIOS. If you enable one of the extended modes, your BIOS basically does the same thing as EZ-drive does, too. EZ-drive is meant for computers that only support "mode normal". But those BIOSes do not display any mode setting at all, so I expect your computer to support different modes.

Rudi_K wrote on 2021-08-11, 12:12:

I think the bios indeed only reconice the 540 limite size, see screenshot below from the EZ-drive.
Can I use the EZ-drive to modify the bios ?
no experience with it 😀

EZ-Drive is a dynamic drive overlay. When you install it via the Fully Automatic Install option, it'll wipe the drive, install itself to the boot sector and allow you to copy DOS system files to it. From then on, every time you boot from the hard drive EZ-Drive will run, bypassing the BIOS' HDD size limit. It doesn't matter what hard drive parameters you have typed into the BIOS, EZ-Drive takes care of that. Be sure to boot from the hard drive first when reinstalling DOS and such.

Thank You Guys, and yes the bios support both LBA and Lage mode.
So now I need to find a way to backup the data and then change the bios, format it and put the backup back and make the disk bootable.

There a default statup disk won't read it anymore, what is the best way to backup ?
put the disk in another PC and use some tool? anyone a tip ?

Drives like this Caviar 2850 are usually used in LBA Mode.
Note that your BIOS may change the order in which it addresses the sectors on de drive in LBA or LARGE Mode. So a drive formatted in LBA mode will not work in LARGE mode and vice versa.

So try to read and backup the drive when set to LBA mode in the BIOS. This should give the best chance of success when the drive is not too bad.