From: "Jack R Payton" :Sent: Wednesday, May 30, 2001 3:04 AM
Subject: Re: [PCBUILD] Replacing Hard Drive


> Mary:
> 
> OK. So, can a FAT32 system address twice as much HDD space? Also, my Mom
> has a Pentium100 system with Win98SE (FAT32) and her 4.2G HDD is fully
> accesible. We have an AMD K6-2/350 with a 17G HDD, partitioned from 2.0
> to 8.5.G - all functional (WinME, FAT32). We haven't added a Promise or
> Ultra controller, etc. Please explain.
> 
> Jack
> 
> > Jack,
> >
> > Here is a quote from Western Digital explaining hard drive
> > limitations.  I hope this helps you understand.
> >
> > "The amount of space available to store information on hard drives
> > is constantly increasing. Computer operating systems and system
> > BIOSs have limitations that are related to specific hard drive
> > capacities. Three capacity points that can affect how your operating
> > system and system BIOS support your hard drive are 8.4 GB, 2.1 GB,
> > and 528 MB.
> >
> > The limitations of your system BIOS and your operating system
> > combined determine your overall system limitation. For example, if
> > your operating system recognizes extended BIOS functions, but your
> > system BIOS has a 2.1 GB drive barrier, you are limited to your
> > system BIOS's 2.1 GB drive barrier. Conversely, if your operating
> > system does not recognize extended BIOS functions, but your system
> > BIOS supports 8.4 GB hard drives, you are limited to your operating
> > system's capability. Your system limitation is based on the lowest
> > functioning barrier."
> >
> > These limitations apply to any hard drive that reports an EIDE
> > capacity of 16320 cylinders x 16 heads x 63 sectors per track or
> > larger.  INT 13 Function 8 is the traditional method used by the
> > system BIOS to access hard drives using CHS (cylinders, heads and
> > sectors per track).  The maximum values the BIOS can report (1024
> > cylinders, 255 heads and 63 sectors) have been exceeded by the 8.4
> > GB and larger hard drives.  Since conventional INT 13 functions use
> > 24 bits to represent addresses, this traditional CHS method permits
> > 8.4GB ( 2(24th)* 512 bytes/sector) to be addressed. To utilize the
> > full capacity of hard drives larger than 8.4 GB, the system BIOS
> > must use extended INT 13 functions and LBA method of addressing.
> > Extended INT 13 functions use 32 bits to represent addresses.  LBA
> > addressing passes a single parameter to represent the address.  An
> > ATA hard disk can accept a single address of 28 bits, so the LBA
> > method of addressing allows addressing of 137.4 GB.
> >
> > If both your BIOS and motherboard do not support extended BIOS
> > functions your drive, no matter how large it is, the drive will only
> > be recognized at the lowest limit of either the BIOS or the OS.
> >
> > I believe what you are referring to is neither the correct BIOS nor
> > drivers can overcome limitations inherent in operating systems. For
> > example, in Windows 3.1x and early versions of Windows 95, 16 bits
> > are available for cluster addressing in the file allocation table
> > (thus the term, FAT16). Since each address specifies a cluster of up
> > to 32KB, the maximum partition size is 2.1GB. So while hard disk
> > drives larger than 8.4GB can be used with these FAT16 operating
> > systems, multiple partitions no larger than 2.1GB each are required.
> >
> > Mary Wolden
> 

Jack,

On the P100 the 4.2 GB hard drive is below the 8.4 GB limit and the OS is Win98se which is using FAT32, so partition size can be larger than 2.1 GB partition limit of FAT 16.  
On your AMD system check the BIOS and see if LBA is being used to access the Hard drive.  It may be set to auto, but LBA is probably an option that is available in the BIOS.  I would gather to guess that neither of these computers is older than 5 years or the BIOS was upgradeable to support LBA and extended INT 13 and has been upgraded.  FAT32 allows partition sizes to be larger than the 2.1 GB limit of FAT 16, not address twice as much hard drive.  

Mary Wolden 

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