What version of OS/2? OS/2 Warp 3 needs to boot inside the first 1024 cylinders.
Here's an older guide that might help get you started- https://www.abc.se/~pa/data/multi-op.htm

superpete wrote:

I have a 500GB disk in an early Pentium class machine that I'd like to quad-boot Windows 3.1/98. NT4 and OS/2. Fortunately the B […]
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I have a 500GB disk in an early Pentium class machine that I'd like to quad-boot Windows 3.1/98. NT4 and OS/2. Fortunately the BIOS can see the entire disk.

The scheme I have is as follows but am open to suggestions 😀

• PART1 - 2GB FAT16 MSDOS/Win3.1 (I assume the boot manager would also live on this partition?)
• PART2 - 40GB FAT32 Windows 98
• PART3 - 20GB HPFS OS/2
• PART4 - Extended Partition
  • Logical 1 - 40GB NTFS NT4
  • Logical 2 - Remainder FAT32 (Data)

Can NT4 be installed in an extended partition? I recall issues with it and disks greater than 8GB, I'm not sure if SP6 resolved it or not. What boot manager is recommended for these Operating Systems (years gone by I had good success with the OS/2 boot manager, but I assume things have improved since).

First of all, "BIOS can see" and "BIOS will allow me to use it" are two different things. According to my experience, 500GB is way huge for a Pentium (socket 7?) board and I really suggest you to check its "recognition" status more thoroughly.

The second thing is, as far as I know, NT based OSes will want to put its boot loader into the first active partition, even if you try to install it on a extended partition or even a second drive.

This would be my partitioning style:

First Disk :

1 - 2GB primary: Windows NT (cannot boot when installed beyond the first 8 GB)
2 - 2GB primary: OS/2 (depending on if it is patched up or not, will not boot when installed after the first 1023 cylinders)
3 - 2GB primary: MS-DOS/Windows 3.1
4 - X GB primary: Windows 98SE (120GB max)

Second Disk (data parititons):

An X GB FAT16 (2GB max)- must for MS-DOS which normally cannot see FAT32, NTFS and HPFS partitions.
An X GB FAT32 (120GB max) - must for Windows 98 which normally cannot see NTFS and HPFS partitions, and FAT16 might be too small.
An X GB NTFS (max?) - must for Windows NT which normally cannot see HPFS and FAT32 partitions and FAT16 partition might be too small.
An X GB HPFS (max?) - must for OS/2 which normally cannot see NTFS and FAT32 partitions and FAT16 partition might be too small.

I also strongly suggest masterbooter. It's support page is a good read for multibooting basics.

http://www.masterbooter.com/support/faq_en.html

As these system's are from the 90's era, they can be used with Os/2 boot manager. Other than that, go for "Extended Fdisk"
Os/2's boot manager (as far as I remember) can use up to 8gb harddrives.
Just play with them two boot managers, and remember that it is only there to change the "Active-Flag" and nothing else.
The biggest problem is, that IDE can only have 4 primaery partitions. This can be solved, by having a second HDD for Os/2.
As the bootmanager can boot from a second harddrive (slave), and use that drives primaery partition.

get a good boot manager like System Command, it will take a lot of the pains away of opsys's fighting for boot control + bootable flags and whatnot..

I had some time over the weekend to give this a go.

tayyare wrote:

According to my experience, 500GB is way huge for a Pentium (socket 7?) board and I really suggest you to check its "recognition" status more thoroughly.

Right you are, the drive seemed to be detected correctly by the BIOS but I couldn't use above 80GB (whcih seems weird I would have expected ~127GB). I dropped a PCI SATA Card in it and had no issues with a spare 1TB disk.

My structure is as follows:

• Primary 1 - 2GB FAT 16
• Primary 2 - 2GB FAT 16 (hopefully change to HPFS) OS/2
• Primary 3 - 40GB FAT32 (Windows 98)
• Primary 4 - Extended
  • Logical 1 - 40GB NTFS (I've put Win 2K on there for now)
  • Logical 2 - Remainded FAT32 Data

This was created with Extended FDisk. My installation was in the following order

1. Install DOS and Windows 3.1 on the first FAT16 partition (I've used Windows98 DOS for it's FAT32 support)
2. Format and sys Partition 3 and copy the Windows 98 Install files on to it
3. Boot off the Windows 98 partition with the Extended FDISK Boot Manager. Install Windows 98
4. Boot off the Win2k CD-ROM and install Windows 2000 onto the extended partition. It will install the NTBoot Manager on the first primary partition allowing you to boot Windows 2000 from that parition

I'm still struggling with OS/2 Warp 4. It won't let me select partition 2 in the OS/2 FDISK so I haven't been able to complete the installation. I suspect I should start with OS/2 then do the other operating systems.

superpete wrote:

I had some time over the weekend to give this a go. […]
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I had some time over the weekend to give this a go.

tayyare wrote:

According to my experience, 500GB is way huge for a Pentium (socket 7?) board and I really suggest you to check its "recognition" status more thoroughly.

Right you are, the drive seemed to be detected correctly by the BIOS but I couldn't use above 80GB (whcih seems weird I would have expected ~127GB). I dropped a PCI SATA Card in it and had no issues with a spare 1TB disk.

My structure is as follows:

• Primary 1 - 2GB FAT 16
• Primary 2 - 2GB FAT 16 (hopefully change to HPFS) OS/2
• Primary 3 - 40GB FAT32 (Windows 98)
• Primary 4 - Extended
  • Logical 1 - 40GB NTFS (I've put Win 2K on there for now)
  • Logical 2 - Remainded FAT32 Data

This was created with Extended FDisk. My installation was in the following order

1. Install DOS and Windows 3.1 on the first FAT16 partition (I've used Windows98 DOS for it's FAT32 support)
2. Format and sys Partition 3 and copy the Windows 98 Install files on to it
3. Boot off the Windows 98 partition with the Extended FDISK Boot Manager. Install Windows 98
4. Boot off the Win2k CD-ROM and install Windows 2000 onto the extended partition. It will install the NTBoot Manager on the first primary partition allowing you to boot Windows 2000 from that parition

I'm still struggling with OS/2 Warp 4. It won't let me select partition 2 in the OS/2 FDISK so I haven't been able to complete the installation. I suspect I should start with OS/2 then do the other operating systems.

I always have some sort of problem whenever I tried installing OS/2 (have some small amount of experience with both 3 and 4) that I need to revise my partitioning plan to make the problems go. I don't exactly remember what I really did each time, but I can suggest making other partitions "hidden" especially the partitions before OS2 partition. I actually can say that it is always good to make any other partition hidden while installing an (non-NT based modernish) OS in a multiboot system.

I can also suggest making the first partition an OS2 one, and moving the DOS to second FAT16 partition. Dos will boot from any partition in the first 8GB, as long as all the prior partitions are either hidden or unreadable (non FAT16).

500GB is a lot of space and you will run into the 134GB limitation in Windows 9x , other limitations in dos, I have found the sweetspot to be around 120Gig for most retro builds, it just has less hassles and worries.

That being said, use Plop boot manager, it is immensely powerful if you know how to use it right, and there is a bit of a learning curve, sadly I dont know how it will react with OS2 , but its worth experimenting.

Superpete, glad you're using OS/2 on that machine aswell!
You already got lot's of tips for your boot manager, so I've nothing much to add.
But I remember I've once used one with OS/2 Warp 3.0 long ago.. It was from Paragon, I think (it did that -hidden partitions- thingy).
I don't know if it's still good though, Plop boot manager and others are probably better.

Oh, and in case you encounter memory problems, here's a tip:
The BIOS setting "OS/2 Memory >64M" is only for old versions of OS/2.
For OS/2 Warp 3.0 and higher this should be set to "disabled" or "Non-OS/2".

And if you're have trouble loading drivers, here's another one: In OS/2, system files should be always in 8+3 format, so avoid long names.
I had this problem with the machine additions of virtualbox; everything was setup right, but they didn't load.
The reason was ofcourse the fact I was using a FAT volume inside my VM (so it can be opened with WinImage).
Eventhough OS/2 supports long file names on FAT, it doesn't support them during boot up. And after I shortened them, they worked.
I guess those -um- respectful developers seem to expect their customers to use HPFS only,
otherwise I can't think of any reason why they used long filenames for their drivers.
That's against the official OS/2 programming guidelines.

You're doing it the wrong way - the OS/2 boot manager must be put in first, and OS/2's fdisk used to partition the disk.

Note that none of the operating systems you mention can handle disks that large without updated drivers.

Disk layout :

Primary - OS/2 Boot manager (probably about 10MB, depends on geometry)
Primary - FAT16 - MSDOS/Windows 3.1. 2GB.
Extended - OS/2 HPFS boot. 400MB. Doesn't need to be any larger.
Extended - NT 4 NTFS boot. At least 500MB, a GB to be safe.
Extended - FAT32 (Win 98), whatever you want. Can't remember '95 limits, probably a driver to increase them.
Extended - NTFS
Extended - HFPS - OS/2 data. 20GB will handle any OS/2 app you care to mention, unless you're heavily into graphics.
Extended - more FAT32 if you want it.

Make sure that whatever size the OS/2 and NT boot partitions are, that the OS/2 boot manager offers the option of 'set installable' when run from the install program. This ensures the partition is entirely within the first 1024 cylinders and bootable.

DOS and OS/2 boot from their own partitions. NT 4 boots partly from the NTLDR files it will stick in the DOS partition, and partly from its system partition. Windows 98 will put some files on the DOS partition, and some on its install partition.

Order to install : 1) OS/2 boot manager. Optionally also OS/2. 2) DOS 3) Windows 3.1 4) Windows 98 5) Windows NT. NT will disable the OS/2 boot manager, it will be necessary to use an fdisk program to set it active again. There are drivers for OS/2 and NT that will handle large disks, these can be applied at install time, or after installation.

My retro system has at least DOS, OS/2, Linux, and OpenBSD on it. Can't remember what Windows versions I put on, but will check tonight.

Technically, yes, you can dual boot OS/2 on a FAT partition with DOS. You really, really, do not want to do so.

Why not install Windows 98 on the same FAT16 partition as MSDOS and Windows 3.1? 2GB is plenty of space for normal operation, and you can always install other stuff to the data partition if you need to. (Just make sure you don't touch anything with a long filename while running DOS.)

In theory, you can then have OS/2 and NT4 on primary partitions, and toggle between them just by setting the active partition without having to worry about the NT4 and OS/2 boot managers. (At least, I assume OS/2 works thay way.)

Realistically I suspect you'll only use NT4 and OS/2 for ten minutes and then forget about them forever, so you might want to just consider storing them on a second separate hard drive and saving yourself the headaches.

ynari wrote on 2016-04-15, 14:29:

You're doing it the wrong way - the OS/2 boot manager must be put in first, and OS/2's fdisk used to partition the disk. […]
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You're doing it the wrong way - the OS/2 boot manager must be put in first, and OS/2's fdisk used to partition the disk.

Note that none of the operating systems you mention can handle disks that large without updated drivers.

Disk layout :

Primary - OS/2 Boot manager (probably about 10MB, depends on geometry)
Primary - FAT16 - MSDOS/Windows 3.1. 2GB.
Extended - OS/2 HPFS boot. 400MB. Doesn't need to be any larger.
Extended - NT 4 NTFS boot. At least 500MB, a GB to be safe.
Extended - FAT32 (Win 98), whatever you want. Can't remember '95 limits, probably a driver to increase them.
Extended - NTFS
Extended - HFPS - OS/2 data. 20GB will handle any OS/2 app you care to mention, unless you're heavily into graphics.
Extended - more FAT32 if you want it.

Make sure that whatever size the OS/2 and NT boot partitions are, that the OS/2 boot manager offers the option of 'set installable' when run from the install program. This ensures the partition is entirely within the first 1024 cylinders and bootable.

DOS and OS/2 boot from their own partitions. NT 4 boots partly from the NTLDR files it will stick in the DOS partition, and partly from its system partition. Windows 98 will put some files on the DOS partition, and some on its install partition.

Order to install : 1) OS/2 boot manager. Optionally also OS/2. 2) DOS 3) Windows 3.1 4) Windows 98 5) Windows NT. NT will disable the OS/2 boot manager, it will be necessary to use an fdisk program to set it active again. There are drivers for OS/2 and NT that will handle large disks, these can be applied at install time, or after installation.

My retro system has at least DOS, OS/2, Linux, and OpenBSD on it. Can't remember what Windows versions I put on, but will check tonight.

Technically, yes, you can dual boot OS/2 on a FAT partition with DOS. You really, really, do not want to do so.

If that is the case "Make sure that whatever size the OS/2 and NT boot partitions are, that the OS/2 boot manager offers the option of 'set installable' when run from the install program. This ensures the partition is entirely within the first 1024 cylinders and bootable." then your example is wrong or not working if the Primary and active DOS Partition is 2GB big and the second one after the 10MB partition of the OS/2 Bootmanager. Therefore if the OS/2 Partition is 500MB, then the primary Dospartition have to be not larger than 1,5GB. Right? What about a secondary FAT16 2GB Partition within the first 8GB of the harddisc as a Data-Transfer partition between DOS and Windows/OS2 ? To my knowledge if we are talking bigger drives like >8GB <120GB the logical FAT16 dospartion will not bee visible if the are partitions behind > 8GB.

dr.zeissler wrote on 2026-08-29, 11:08:

To my knowledge if we are talking bigger drives like >8GB <120GB the logical FAT16 dospartion will not bee visible if the are partitions behind > 8GB.

Nice necro. Haven't u read the warning before posting?
Last post was older than TEN YEARS!

There are 2 types of extended partitions. One CHS one (05h) that can be used by DOS. One LBA one (0Fh) that can be read by Win9x too. However, at least FDISK does not like 2 different types of extended partions at the same time.

Even if it is 100 Years, the topic is still valid. Why should I post a new one, the chances are much higher that people that were involved before will step in too and perhaps have some upgrades.
If we cut off posting on older topics we will get fragmented and unusable single topics with no "mehrwert" as we call it locally.

This is exactly what I was looking for.
Nice!

You won't have enough partition table entries.
DOS takes 1 (does not boot from extended)
NT takes 1 (afaik does not boot from extended)
OS/2 bootmanager takes 1
Extended Partition (CHS, type 05h) takes 1
OS/2 can be installed and booted on extended
Data transfer partition 2 GB FAT16 can be installed on extended
If you can boot OS/2 without bootmanager you would save 1 partition table entry that can be used for Win9x FAT32 partition, starting at cylinder 1021 or 1022 up to end of disk

That's the layout I use on my 486 with 4 up to 8 GB disks.
When I do not use OS/2 I use the boot manager from Windows 2000.
When I use OS/2 I try to install this first as it is pesky with boot manager.
I do not rely on OS/2 boot manager to hide/unhide partitions.

So nothing new.

The CHS/LBA thing is new to me. My later machines have LBA entry in the Bios and the hard disk of the current project is about 40GB.
I never figured it out to get a datacopy-partition for dos with 2GB logical partition if I use space that is over the 8GB limit. If I create a partition over the 8GB limit, the former 2GB logical partition that lies in the 8GB limit is not accessible for dos anymore. The only thing to fix this is having another hard disk in the system starting with a primary 2GB FAT16 partition. In that case the extended partion after this primary 2GB dos-partition does not change anything even if it exceeds 8GB.

All of my multi boot-setups work with XFDISK and the setting for "hiding primary partitions". That works very well but it limits the bootable OS. Using on stable FAT16 that is always C: can perhaps increase the possible amount of bootable OS but there are circumstances that I don't like. Bootfiles from different OS, hardcoded installs like the PM-Manager for OS2 always uses C: for installation etc. The other thing is on later Systems I always install AmigaOS and Linux too.

I think I can do the setup described above without the OS2 Bootmanager and XFDISK instead. Should be exact the same process. I could install two other primary OS too but that would lead to having to start DOS once, in order to be able to start the OS that rely on the C: Data for being bootable (boot files) so there is no real benefit from that.

here you can see on an earlier machine how I install such multi boots.
https://youtu.be/uylD7rDSorg?si=4PKW1GuhKyDGQ08F

EDIT:
Ah I made a mistake, only the OS/2 Bootmanager can boot OS/2 out of logical partitions. So I can't use XFDISK for that. Using the OS/2 Bootmanger is not so handy and easy/fast to setup and fix if there are problems and the hard disk driver MUST be up do date in order to partition the drive with OS/2. Using XFDISK and preparing a first OS/2 drive at the beginning of the hard drive mostly fixes everything for OS2. Fdisk of OS2 fails for the most time, but the OS2 installer is to 99% happy if it finds the 2GB HPFS partition on the start of the drive.

But I will checkout that type of setup in order to find out if it's better than what I do normally (video)

EDIT2:
OS/2 Bootmanager is pretty useless. It only supports 4 boot entries. I made my base install multi boot as usual.

This may be a good time to mention that DFSee has a modified OS/2 boot loader that raises many limitations including the number of boot entries and LBA support.

I am using it on the Book386 to boot DOS/Win3.x, Win95, NT 3.51, OS/2 Warp 3, FreeDOS, and several Linuxes from a single 16GB CF card.
The partition layout is 3 primary partitions (OS2BootMgr, a DOS FAT16 one, a Win95 FAT32 one) and logical partitions for the rest of OSes (NTFS NT one, HPFS OS/2 one, FAT32 FreeDOS, ext2 for Linux, etc.) .
All of them can launch directly from the OS2BootMgr menu.

Because the Book386 doesn't do LBA, I am using Ontrack as DDO. (Ez-disk is probably easier to work but I conceptually prefer the "shifted disk" approach by Ontrack as it allows most real mode bootloaders to work unmodified; on the other hand protected mode bootloaders and OSes need changes, but most era OSes do support Ontrack natively).

So for example, to boot OS/2, the chain goes something like:
BIOS -> Ontrack MBR (provides int13) -> DFSee-installed MBR (int13 capable) -> DFSee-installed OS2BootMgr -> DFSee-installed VBR in the OS/2 partition (int13 capable) -> OS/2 kernel (updated with latest fixpack since I think original one doesn't use int13).

DFSee itself is immensely useful to debug this monstrosity, it will show which boot records you are using all along the way and always install LBA-capable ones. It also allows you to avoid the very-fragile OS/2 Warp 3 FDISK.

Suffice to say that booting NT from a logical partition is possible and trivial, many bootloaders can do this on their own. The OS/2 boot manager is however stupid when it comes to NTFS partitions, so you have to apply the "hidden sectors" trick manually - but just once. (DFSee doesn't do that and worse: its "fix partition table" command will undo this trick).

It is booting from an OS/2 logical partition that is a bit more convoluted, as far as I remember OS2BootMgr is the only period-correct boot manager that can do it. And even from recent bootloaders I am not sure which can do it natively; I have patched GRUB4DOS in the past to do it, the OS/2 boot protocol is very well documented.

I am quite sure you'd likely have no issues booting the DOS OSes from a logical partition either. But it's nice to keep something that can be "natively" booted to diagnose problems.

That said I think the bootloader is not really that important piece here and most of the time you are going to be fighting the stupid idiosyncrasies from the various OSes. E.g. OS/2 Warp 3 outright refuses to show any partition over the 1024 cylinder limit as installable (even on Ontrack systems). NT refuses to install to logical partitions, and is so crappy overall that sometimes NTLDR and the NT kernel will disagree on how to number the partitions you have, leading to disaster. Even the latest official updates are not enough, only the Win2k boot sector and NTLDR can seemingly boot from LBA/Ontrack, and on NT 3.5x you need a patched atdisk/atapi.sys for LBA support too. So be ready to be "transplanting" OSes from temp installs to your final disk a lot (plant analogy really appropriate here).

Never thought that "on track" systems allow multi boot. thx!

dr.zeissler wrote on 2026-08-30, 11:33:

Never thought that "on track" systems allow multi boot. thx!

It's not Ontrack that provides multi boot, it's the OS/2 boot manager. Ontrack is a DDO, it just provides LBA support (i.e. > 1024 cylinder support , > 8GB support) for systems whose BIOS lack it, and then boots whatever is on your one "virtual" MBR.

From that point you have to ensure that _all_ the bootloaders and bootmanagers in the entire boot chain support LBA (this also applies on systems where the native BIOS supports LBA), otherwise you get corruption everywhere.