If you have both systems on a separate disk, I think you'll only have to use the BOOT MENU BIOS when you start the computer to make the choice - that's where you choose the disk the PC is supposed to boot from. Typically, the BOOT MENU is triggered by pressing an F key (for example, F11) during the POST process.
I don't know any way to select running OS on another disk after a PC booted from a different one.

Might it be solved by simply adding D:\="Microsoft Windows 98" under [operating systems] in your XP boot.ini (where D: is the drive Win98 is installed on, as seen by WinXP)?

Alternatively, you may solve it by simply installing Win98 boot files on both hard drives. The boot portion of Win98 is just fancy DOS, and needs nothing other than a couple of files. The actual Win98 directory can be on any drive, and you can point MSDOS.SYS to that directory. Of course, this means that the partition on the first drive you are booting from must be FAT32-formatted.

Kahenraz wrote on 2022-07-01, 08:36:

I have installed Windows 98 on a disk all by itself, then removed that disk and installed Windows XP on another.

Given you did this then you are starting from a bad place as I suspect both systems are installed on C:

What I do on my systems in have both disks installed, install Windows 9X on C: then install Windows NT4/2000/XP/2003/... on D:, E:, F:,...

When you do this boot.ini will be on C: and will by default offer Windows 9X + NT4/2000/XP/2003/...

Note: I have both WME + NT4 on C:\ which in general is a bad idea!

Both drives C... depends, if the XP drive is NTFS, dos won't see it and thus, shouldn't be a problem.

weedeewee wrote on 2022-07-01, 13:19:

Both drives C... depends, if the XP drive is NTFS, dos won't see it and thus, shouldn't be a problem.

So what? WXP will see the C: that W9x is on and may are may not decide it's C: and it's on D: when lots of things in the registry say C:

The guy will end up with a total mess and I feel it's better to re-install XP now and have a clean setup moving forward

With WXP as the first drive in NTFS, it will see itself as C and the dos drive as D,
and with DOS as the second drive not being able to see the NTFS drive, DOS will also see itself as C

weedeewee wrote on 2022-07-01, 13:51:

With WXP as the first drive in NTFS, it will see itself as C and the dos drive as D,
and with DOS as the second drive not being able to see the NTFS drive, DOS will also see itself as C

Not on my system

Well of course not on your system.
Out of curiosity, which drive contains which partition on your system?

weedeewee wrote on 2022-07-01, 14:12:

Out of curiosity, which drive contains which partition on your system?

Why do you need to ask this ? Given what in the boot.ini I posted it should be obvious the system only uses one physical drive for all the OSes so I guess you need to learn more about boot.ini.

I have other systems with multiple physical drives, but the number of physical drives does not affect things other than you need multiple physical drives to easily end up in the position OP is in.

Why did you expect I would read your boot.ini ? OP was talking about two drives, each with an OS, and then you come along with a bunch of OS on one drive.
Anyway, enough. you've had your say, I've had mine. This isn't adding anything to OP question.

weedeewee wrote on 2022-07-01, 14:59:

Why did you expect I would read your boot.ini ?

Because I would have before making any of the posts you made.

red-ray wrote on 2022-07-01, 14:45:

I have other systems with multiple physical drives, but the number of physical drives does not affect things other than you need multiple physical drives to easily end up in the position OP is in.

weedeewee wrote on 2022-07-01, 14:59:

OP was talking about two drives, each with an OS, and then you come along with a bunch of OS on one drive.

Clearly you don't read posts before replying as I clearly stated the number of physical drives does not affect things.

red-ray wrote on 2022-07-01, 15:14:

Enough.

I decided to plug both drives in with the XP drive set to primary in the BIOS. Despite everything being recognized by Windows XP setup and after booting, it does not configure boot.ini whatsoever to provide a dual boot option. I suspect that this is only something that it does when installing to the same disk.

I tried reinstalling twice, to try and have the dual boot configured automatically, but without success. I also tried to set the second boot option manually as "D:\", but this just causes the computer to reboot when this option is chosen at the boot menu. I'm pretty sure that I need to do something else, in addition to pointing it to the other disk.

Windows 98 is running FAT32 and XP is NTFS, so I'm not worried about any file system visibility creating confusion, as the NTFS partition should remain hidden to Windows 98.

I think the issue is that I'm trying to chainload the NT and 98 bootloaders, which doesn't seem to be possible with NTLDR. This would however be possible with something else such as GRUB4DOS or a Linux bootloader. This isn't what I want though. I was hoping that I could keep both bootloaders intact, without having to choose which one I wanted to clobber.

The correct way to do this is to use a FAT partition on the primary bootable drive that is also the C drive, and have Windows 98 create its bootloader there. XP will then clobber it with NTLDR, and can then dual boot from later. What you can't do is use NTFS the partition bootable partition and then chainload the Windows 98 bootloader, as it can't run from the NTFS partition.

This is my interpretation of the data, anyways.

I agree Having each OS on a separate drive is best, if not have each in their own partition and have the first with oldest OS. It is easier to create a boot menu that way that works and does not mess with the other drives.... Also: in XP, Win7, etc you can use a Regedit hide/mask the other partitions to keep say XP, etc from monitoring the drive with System Restore. Just turning those drives off in "System Protection" does not force that OS to not "mess" with those drives or restore points.....just my experience.

Kahenraz wrote on 2022-07-01, 22:59:

I decided to plug both drives in with the XP drive set to primary in the BIOS. Despite everything being recognized by Windows XP setup and after booting, it does not configure boot.ini whatsoever to provide a dual boot option. I suspect that this is only something that it does when installing to the same disk.

I tried reinstalling twice, to try and have the dual boot configured automatically, but without success. I also tried to set the second boot option manually as "D:\", but this just causes the computer to reboot when this option is chosen at the boot menu. I'm pretty sure that I need to do something else, in addition to pointing it to the other disk.

Windows 98 is running FAT32 and XP is NTFS, so I'm not worried about any file system visibility creating confusion, as the NTFS partition should remain hidden to Windows 98.

Boot.ini does not contain the boot record for Windows 98 - this is contained in Bootsect.dos, which is created/captured during the initial XP installation whilst DOS, 98, etc. is already present on the disk/partition. The Boot.ini file only tells XP there is another option to boot, be it XP, XP with various switches, another OS, etc. You must be able to boot into Windows 98 before installing another OS (like NT, 2000, XP, etc.) for Bootsect.dos to be created. If you're not able to boot into 98, before you reinstall, did you try "SYS C:" for the Windows 98 partition?

It's possible to rebuild Bootsect.dos, but I'm not sure of the level of challenge. The alternative is to reinstall XP with 98 already installed.

Yes, I tried this. I switched the Windows 98 drive to the primary boot drive, then generated a bootsect.dos. However, NTLDR is still unable to boot from this after I swap the XP drive back to the primary disk. I don't think it's possible to boot to Windows 98 if it is not set as the primary drive in the BIOS.

I THINK that the problem is that the Windows 98 bootloader is designed to boot from the active disk. If I try to chainload it from the D drive, then it gets confused as it tries to boot from the C drive, which is the wrong disk. I tried to reinstall Windows 98 with XP as the primary disk in the BIOS; I booted to a floppy where the slave FAT32 disk was detected as the C drive, but the Windows 98 installer screamed about needing a FAT partition for the bootloader, which is why I think it can't work unless it's the primary disk in the BIOS.

Kahenraz wrote on 2022-07-02, 02:13:

Yes, I tried this. I switched the Windows 98 drive to the primary boot drive, then generated a bootsect.dos. However, NTLDR is still unable to boot from this after I swap the XP drive back to the primary disk. I don't think it's possible to boot to Windows 98 if it is not set as the primary drive in the BIOS.

I THINK that the problem is that the Windows 98 bootloader is designed to boot from the active disk. If I try to chainload it from the D drive, then it gets confused as it tries to boot from the C drive, which is the wrong disk. I tried to reinstall Windows 98 with XP as the primary disk in the BIOS; I booted to a floppy where the slave FAT32 disk was detected as the C drive, but the Windows 98 installer screamed about needing a FAT partition for the bootloader, which is why I think it can't work unless it's the primary disk in the BIOS.

Yes, you're right. In that case, you make a small 256MB C: drive. Install Windows 98 on the D: and Windows XP on the E:

But I don't know why you won't install Windows 98 on C: as primary and then install Windows XP as secondary on the D:? You don't want a FAT C: disk? I might be misunderstanding (and/or I didn't read through the thread properly), but it seems you are stuck on a design which has Windows 98 as a secondary disk? Is this right? What is the reason, I'm curious?

Keeping the disks and OS bootloaders separate makes it easier to wipe/reinstall and do any kind of whatever maintenance when tinkering and swapping hardware. It's also not unusual to install something that blows away Windows 98 by making it unbootable or unstable by overwriting some registry key or file on disk. It's a convenience thing.

The disk I have for XP is a 512MB SSD. I'm currently tinkering with adding an additional partition for Fedora and using GRUB to chainload the other two operating systems. This would also give me access to Linux for whatever, and it would also fulfill my bootloader requirements. Since this would all be done on the second disk where Windows XP is to be installed, I would retain the luxury of being able to mess with Windows 98 on the other disk as I please.