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22 votes
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How did Drive Overlay programs break BIOS disk barriers on older PCs?

The reference for this is DEW Associates’ pages on the topic. Multiple barriers have existed in the history of hard drives on PC compatibles. The main ones are the barriers at 528 MB (504 MiB) barrier,...
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19 votes
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Default (as opposed to physical) read/write heads - what are they?

The physical geometry how many heads the drive actually has is not the same as the logical geometry of how many heads is presented to the PC by the drive. By translating the geometry, the drive can be ...
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15 votes
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Hard coded hard drive BIOS geometries

The tables were built using the parameters for various real hard drives. For example, type 1 is used for the original Shugart drives used in the PC XT (ST506). So the intention was for the drive types ...
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13 votes
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How can I edit CMOS hard drive geometry settings on a 1991 PC?

In all the BIOS setups I was dealing with that have similarly 47 drives to chose from the first or the last one was editable directly in BIOS SETUP for manual settings. Sometimes the manual settings ...
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13 votes
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Can DOS 6.22 recognize more than 504MB when the BIOS only supports CHS?

It can be done using a third-party "disk manager", such as OnTrack Disk Manager and EZ-Drive. At the end of the DOS era, these came bundled with many hard disks. https://en.wikipedia.org/wiki/...
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12 votes

How to determine BIOS-provided (INT 13h) hard disk geometry, and how to fix the MBR partition table to agree with it?

If you can manage to boot the computer from a DOS floppy or some other device, you should be able to use the classic partitioning tool, Ranish Partition Manager. (I recommend version 2.40 or 2.44; ...
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12 votes
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How can the number of cylinders be different from the number of tracks?

As far as I can tell, the first edition of the IBM 5150 Technical Reference is the only IBM manual which mentions 45 cylinders. Few Technical References document the FDC, which is where the “45 ...
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11 votes

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

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 ...
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10 votes
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Why is QEMU cutting off the last cylinder of the disk image?

QEMU is not at fault here. The discrepancy comes from the BIOS. When I create a disk image as described in the question, then attach it to a QEMU virtual machine and use the info qtree command in the ...
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10 votes

Default (as opposed to physical) read/write heads - what are they?

Modern hard drives are not addressed by Cylinder, Head and Sector (CHS) coordinates, but by Linear Block Address (LBA). This is mostly due to the number of sectors per track changing across the width ...
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  • 16.1k
10 votes

How can I make an 80 GB hard drive work with an Asus P2L97 motherboard?

You need a BIOS update. Version 1009 from November 1999 already fixes it according to release notes. It is the final official BIOS version and newer beta releases exist, but must be chosen carefully ...
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9 votes
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Booting from SD card on a Compaq LTE 4/75 – DOS 6 works, Windows 95 doesn't

The problem is in the geometry. Not in the physical disk geometry, but rather in the translation how the BIOS must translate the geometry for DOS when using disks larger than 1024 cylinders. The ...
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6 votes

Booting from SD card on a Compaq LTE 4/75 – DOS 6 works, Windows 95 doesn't

Whew, I've got it solved! I took one of the disk images with Windows 95 installed on it, and examined it with a hex editor. I noticed that when the Windows installer program initially sets up the ...
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6 votes

How to determine BIOS-provided (INT 13h) hard disk geometry, and how to fix the MBR partition table to agree with it?

There are various different methods of converting the drive physical geometry to logical BIOS geometry. It sounds like the drive was originally been used with "ECHS" or "Large" ...
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6 votes

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

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 ...
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5 votes

How can the number of cylinders be different from the number of tracks?

Floppy disk drives could usually mechanically access more than 40 tracks, but only 40 were actually used, "formatted". First track is on the outer edge of the disk, there is a detector than ...
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  • 1,446
4 votes

Default (as opposed to physical) read/write heads - what are they?

Some older computers used to identify 512-byte sectors by specifying a combination of a head number, sector number, and cylinder number. For historical reasons, the head number was often limited to ...
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  • 28.1k
4 votes

Compaq Contura Aero 4/33C - moving data to CF/IDE disk - No operating system detected

Because these drives have different geometries and multiple partitions, you can't dd the whole thing in one pass and expect everything to work. In particular, your DOS partitition which was located ...
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4 votes

How can I make an 80 GB hard drive work with an Asus P2L97 motherboard?

With the upgraded BIOS, the asker’s computer seems to have locked up in a pretty curious moment. This gave me an idea what might be the cause, so I decided to take a stab at disassembling the BIOS to ...
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4 votes
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How can I make an 80 GB hard drive work with an Asus P2L97 motherboard?

Solved by reducing the HDD capacity to 33.82GB with OnTrack Disk Manager 9.57 on floppy disk (Advanced option > Maintenance Option > Utilities > Set Drive Size). It works! (I have another ...
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3 votes

How can I make an 80 GB hard drive work with an Asus P2L97 motherboard?

If installation is your issue, OnTrack Disk Manager 9.57 is available as a bootable disk image. You could just boot your Pentium 2 off its install disk and let it do the rest. Alternatively, if you ...
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  • 4,563
2 votes

Compaq Contura Aero 4/33C - moving data to CF/IDE disk - No operating system detected

Like Ken Gober said, you can't expect to clone drives with different geometries this easily :) Also you should make sure the BIOS recognizes the drive properly. If it's an early revision it might be ...
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  • 251
1 vote

Booting from SD card on a Compaq LTE 4/75 – DOS 6 works, Windows 95 doesn't

This is a logical–physical geometry mismatch. Like @Justme’s answer explains, the ‘logical’ geometry used by the BIOS disk interrupt services, and the ‘physical’ geometry reported by the disk ...
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1 vote

Hard coded hard drive BIOS geometries

That custom started in a time where only a few tens of hard drive models plausibly usable with PC compatibles was on the market. This was the time of ST506 (MFM) style interfaces, and installing hard ...
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