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DOS compatibility mode disk drive

Posted on 1998-11-29
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Last Modified: 2013-12-16
I recently bought a used laptop, loaded with WIN95a (not by mfr).  It crashed a LOT; usually on Windows startup.  

After reloading Windows, the problem went away, but I found that under Performance it stated I was not getting optimal performance because my hard drive was using DOS compatibility mode.  

I did a hardware setup in Windows, it found the hard drive controller, installed the required EIDE driver, and the DOS compatibility mode went away.  But the computer began crashing again (sometimes have to boot 4 or 5 times to load Windows).  I deleted the hard drive controller in Device Manager, it went back to DOS compatibility mode, and once again the problem is gone.

What is happening, why can't I get out of "real (DOS compatibility) mode" and use the Windows driver for the hard drive controller?

I checked with FDISK, and the drive is partitioned with FAT16.  Is this the problem?  From what I read elsewhere here WIN95a (what I have) uses FAT16 while only 95b uses FAT32, although I do not know if this is true.  I wanted a more definitive answer before I undertake starting all over and re-partitioning the drive.  Can I even partition FAT32 with 95a?

Finally, how much performance am I actually losing by leaving this thing in DOS compatibility mode?

Thanks!
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Question by:porear
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by:RoadWarrior
ID: 1759804
It might be a hardware thing with the laptop, some models do not like using 32 bit disk access, that may be the trouble. Has anyone else more info on that?

RoadWarrior
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by:porear
ID: 1759805
If this helps, its an Epson 866C, 486/66, 8 Meg RAM, with Enhanced IDE hard disk controller (350 Meg drive).  The drive itself is a Toshiba T95072.  Thanks!
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by:sKiiKe
ID: 1759806
First search the registry with REGEDIT for entry NOIDE=1. Back the registry up before alterations. Delete the entry and boot up.
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by:sKiiKe
ID: 1759807
And after that scan for viruses. Sometimes MBR or bootsector viruses cause DOScompability mode
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Jason_S earned 100 total points
ID: 1759808
Win 95a will only run FAT16.  95b will run either FAT16, or FAT 32.

A system of this type/vintage with this much (little) memory will only run DOS compatibility mode.  The only way to attempt to get the drive to run 32 Bit, is to upgrade the memory to at lease 16Meg.  Even then, it is not guaranteed to run 32 Bit.

As far as performance loss, a system with a faster processor, and more memory will run noticeably slower in DOS compatibility mode, as opposed to 32 Bit mode.  but in this system, the bottleneck is the Memory and Processor.  So with this configuration running 32 Bit, you would not notice any increase in performance if you could get it running and stable.
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by:porear
ID: 1759809
Hehe well at least I now know not to waste any more time on this thing (drives me nuts when I have to reboot that 66 MHz repeatedly).  Luckily its for the computer illiterate folks to do e-mail, so they won't kow what a dog it is.  Thanks!
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by:porear
ID: 1759810
This still seems a little unusual though... the floppy isn't using this mode and runs fine.  I have had a 486/66 desktop in the past with 8 MEG and never experienced this problem running Win 95...
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by:Jason_S
ID: 1759811
The floppy doesn't use 32 Bit.  It always basicaly uses what would be known as DOS Compatability mode.

With the old 486/66 you may either not have noticed this, or it was just at the threashold where it would run 32 Bit.  Still pretty slow with 8 Meg.
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by:porear
ID: 1759812
Originally, both the hard drive and floppy showed up under Performance as using MS DOS compatibility mode.  After running hardware setup, Windows installed drivers for both and both a hard disk controller and a floppy controller showed up under Device Manager.

Now, after manually deleting the hard drive and its controller under Device Manager, the hard drive has gone back to DOS compatibility mode, but the floppy has not and still retains its listing under Device Manager along with a controller.

I would try adding RAM, but not really worth the cost to upgrade this machine... Thanks again
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by:porear
ID: 1759813
The problem is NOT a lack of RAM.  I have been able to get the machine to boot properly and recognize the hard disk controller in 32 bit mode, but I have to remove the PCMCIA controller under Device Manager first.  Apparently there is a conflict between these two devices.

And yes, the machine runs MUCH faster when not in DOS compatibility mode!  Hey Jason, gimme my points back!  Just kidding, I'll be glad when I get this resolved!  I'll post if I get it completely fixed.
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by:Jason_S
ID: 1759814
What are the resources used by PCMCIA?  Are you using any PCMCIA devices?
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by:porear
ID: 1759815
I'm here at work now, so I don't remember the I/O addresses, but the PCMCIA controller uses IRQ 11, its modem uses IRQ 15, and the hard disk controller is at IRQ 14.

I've been working with a Microsoft support engineer for a few days now, (I'm actually pretty impressed, these guys are really helpful) and we think we've narrowed it down to a flaky hard drive controller.  If so, I'll give up.  This is a X-Mas gift for mom and dad, who won't ever know they're getting degraded performance.  It'll just drive me nuts when I go and visit!
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by:Jason_S
ID: 1759816
Try changing the modem to another IRQ.  The controller uses IRQ15 by default.  Or simply leave the modem out, and see what happens with the controller.
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by:porear
ID: 1759817
Tried all of that... same results.  Its the hard disk controller thats the culprit, but its inconsistent.  Crashes at different points in loading Windows, in different VxD modules.  Sometimes (small percentage) everything loads normally.
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by:porear
ID: 1759818
The problem appears to be intermittently functioning sectors on my hard drive.

Scandisk either reports these as good or locks up when checking them, before repairing.  I'm searching for a utility that will allow me to manually mark sectors/clusters as bad on the hard disk.
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by:Jason_S
ID: 1759819
Check the connections on the drive if possible to see that they are seated properly. (probably not the problem)  I suspect that the drive is prone to fail over time.  
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