How can I tell if my old PC supports > 137 GB hard drives?

Question

I have an old PC from 1999 that has an ASUS P5A motherboard. When I power it on, it says ASUS P5A ACPI BIOS Revision 1011 Beta 005 and 05/02/2002-ALADDIN5-<<P5A>>:

I recently read that up until 2001 or 2002, there was a 137 GB limitation for hard drives. This PC is showing a BIOS date of 2002/5/2, and I cannot find any information on whether it supports hard drives larger than 137 GB.

I connected a 160 GB hard drive as master on the secondary IDE channel, and then in the BIOS, I told it to auto detect the hard drives. This is what it showed for the secondary master:

I am not sure which of those options to select. But does it even matter? I tried entering in my own garbage values for the secondary master (CYLS=1, HEAD=1, PRECOMP=1, LANDZ=0, SECTORS=63, MODE=NORMAL). Then I booted the computer using the Ultimate Boot CD and ran IBM Drive Fitness Test, and it detected the correct secondary master hard drive model number along with the 160 GB size.

If IBM Drive Fitness Test could detect the hard drive size correctly, does that mean that the BIOS supports hard drives larger than 137 GB?

Also, if a program is able to determine the correct hard drive size despite the incorrect hard drive parameters that I entered in the BIOS, then what is the point of either auto-detecting the hard drive or manually entering the correct parameters in the BIOS?

Answer 1

Very briefly:

The way harddisks are addressed changed over time. Originally, you'd specify cylinder/head/sector (CHS), then it switched to logical block addresses (LBA), and the commands for those went through various versions with an increasing number of bits. As you can read on Wikipedia, LBA first used 22 bits, then 28, then 48.

So you need to distinguish between (1) what does the BIOS support and (2) what does the OS support.

Actually, your link from the comments already gives an explanation:

"Operating systems that do not have 48-bit LBA support enabled by default (such as Microsoft Windows 98, Microsoft Windows Millennium Edition (Me), or Windows 2000) that are installed on a partition that spans beyond the 28-bit LBA boundary (137GB) will experience data corruption or data loss."

and

Many computer BIOS will be unable to recognize hard disks over 137 GB, since they are limited to using only 28 bits to keep track of the LBA sector count.

So you can run into trouble with your OS if you have a large harddisk with a partition for that OS that is larger than or placed at a position greater than the LBA size the OS sizes.

And you can run into trouble with your BIOS if you try to boot from a partition that is larger than or placed in a position that is greater than the LBA size supported by the BIOS.

This means:

• If you do not want to boot from that disk, it doesn't matter at all if the BIOS "supports it".
• If you want to boot from that disk, make sure you boot from the first partition. I'd also assume as long as the bootstrap from BIOS works, that partition can be even larger than what the BIOS supports (but I never tried that, and the simplest way to find out is to try). However, this probably depends on the first stage of the bootstrap process that uses BIOS calls also to be located early enough, which may be difficult to control.
• You should make sure that the OS you boot can deal with all partitions you want that OS to access. If there's potential trouble, make the partition small enough.
• If all else fails, you can make a first small partition with something on it that can chain boot to other partitions probably would work.

This means you should select LBA, and find an OS that supports the partition size you want to use, or make the partition smaller.

Answer 2

That BIOS screen clearly says that it detects the drive as roughly 8 GB. The parameters say 16383/16/63 as so this BIOS cannot detect or provide the extended disk services that would allow the drive to be used beyond the 16383 cylinders, or the 8GB limit.

It does not matter if another program can detect the size properly by communicating with the drive directly - it still can't be used via BIOS. It can boot an OS if it is on a partition below the 8GB limit. An operating system or drive overlay with a driver that can access drives larger than 137GB can be used to access the drive.

It is best to select the first option, LBA, if you wish to have best compatibility.

Answer 3

edit: According to this document here https://www.seagate.com/support/kb/disc/tp/137gb.pdf, some IDE or PATA controllers had driver updates available which allowed exceeding the 127GiB limit. The document also says that an IDE or PATA controller hardware change is necessary in some cases. So saying that it is a hardware limit is technically true if the IDE controller and driver are considered to be one unit, which is usually the case with proprietary Windows software.

The 127GB (LBA28) limit is an IDE controller limit. There is no software work around because the IDE controller company didn't make a new driver in many cases. If there is no proprietary driver update to fix it, there wouldn't have made a BIOS update to fix it either. You have to buy a PCI add in card that supports IDE LBA48 or SATA and use a cheap SATA to IDE converter. If it supports ATA133 it should support LBA48. If it supports ATA66 it won't support LBA48. Otherwise check the documentation.

Your hardware is too old to support LBA48. You probably cannot access beyond 127GB on any IDE hard drive you connect to that motherboard, using the proprietary drivers.

If a program is able to determine the correct hard drive size despite the incorrect hard drive parameters that I entered in the BIOS, then what is the point of either auto-detecting the hard drive or manually entering the correct parameters in the BIOS?

Those Cylinders, Heads, and Sectors parameters in the CMOS setup are for original INT 13h BIOS access to the hard drive, which is the original legacy way of hard drive access that is limited to 8.4GB. Any BIOS since the late 1990s will support extended INT 13h access which is a 64-bit number. Any version of DOS, or boot loader, or disk utility that supports partitions greater than 8.4GB will use extended INT 13h. So most of the time it doesn't matter what values you put in the CMOS setup in these situations. Sometimes software will use original INT 13h access though in which case there will be problems if the CHS values change. Most operating systems that are more advanced than DOS use their own drivers to access the hard drive, so the CMOS INT 13h method is not used, and so the CHS values for the drive in the BIOS won't matter.

Edit: I had previously said that this was a hardware limit, but it appears that I was mistaken.