That is clear, but the access to the drive and the other partitions is drawn to the load of "ontrack.sys" as I thought.
This is why I never made a multiboot on my Systems with Ontrack.

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

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.

OS/2 boot manager is not perfect, and there will be ways of working it out mathematically based on the BIOS and the installed disk, but this is largely speaking a waste of time. Install the boot manager, then add an increasingly larger/smaller partition until it is no longer 'set installable' to find the boot limit for OS/2.

You could try using Airboot (used in ArcaOS) to boot OS/2 too, it is freely available, but installing will probably be a bit of a pain.

The *bootable* DOS partition must be a primary partition and should be the first partition on the disk. You can also have extended DOS partitions above the boundary. Earlier NT versions put their boot files on the first primary DOS partition also, but everything else goes on an NTFS partition (that can be any point on the disk).

OS/2 can boot from an extended partition, as can Unixes.

One of my OS/2, DOS, and Unix systems (mostly used for DOS) - a Gateway pentium 2 300 with a 128GB SSD, is laid out as follows :

Boot manager 7MB
PC DOS 643MB (primary) (visible by DOS and OS/2. C: in DOS, C: in OS/2)
OS/2 boot partition (extended partition, logical drive) 1106MB D: in OS/2
Extended FAT partition 2031 MB (visible by DOS and OS/2) D: in DOS, E: in OS/2
Extended FAT partition 1851 MB (visible by DOS and OS/2) E: in DOS, F: in OS/2
227MB free space (can't remember why - probably reserved in case I want to put on another OS)
Linux partition, type 83 1027MB - Linux boot
OpenBSD partition type A6 '1027 MB'
-- I *think* this is the point at which above which the combination of the BIOS and OS/2's boot manager stops booting operating systems
'free space' 20481MB. This is a lie, OpenBSD has been deliberately installed into the partition above and this 'free space'.
several partitions between 1 and 20GB of type 83 for Linux /var /opt etc and then /home

They all boot successfully.

643+1106+2031+1851+1027+1027 =7.685

You are in the 8GB limit. No Problem, create another 2GB Partition and every dos-partition after the first primary will be gone.

8GB - yeah, that's probably about right. I can never remember all the limits - 540MB, 1024 cylinders, the 8GB limit, then 138GB (isn't there some stuff that doesn't like >32GB too?)

It is, of course, a tradeoff. Around 4.5GB is sufficient for all the DOS games I want to run, especially given back in the 286 days mine had a 40MB hard disk (although admittedly that was doublespaced to heck). You could also use OS/2 or one of the Unixes on the same system to shunt data between the DOS FAT partitions and the >8GB HFPS/ext 3/FFS partitions.

If I wanted a pure DOS system with acres of storage I'd stick in an XTIDE BIOS, then a DOS that supports sufficient logical drives or FAT32 and use that. Sadly, OS/2 does not like the translation XTIDE does, a pity as it works really well in DOS.

Sadly, OS/2 does not like the translation XTIDE does, a pity as it works really well in DOS.

That's interesting. Is there more detail to that?

I am using Ontrack and it works well.

The OS/2 installer is a bit more picky than its BootMgr. The installer will outright refuse to mark a partition spanning the 1024 cylinder limit (i.e. 8GB) as installable, no matter the lba/i13x support, but a sufficiently updated bootmgr can use i13x to boot partitions over that limit. Or the one provided by DFSSee.

No - it fails extremely early in the boot process, and even if the partition is low down in the hard drive sectors. I imagine to progress this it'd need to be disassembled, and it's really not on the list of projects I want to do any time soon.

Ontrack is useful, but the problem with all these adaptations (custom BIOSes such as XTIDE, Ontrack etc) is they work well with some operating systems/boot managers, and not with others. Boot Manager is definitely not ideal, but I understand where I stand with it, and it's possible to boot pretty much anything from it.

I haven't checked if ArcaOS has fixed this - from the looks of the install instructions it has, but my specific install starts with a 3.6GB boot, with other partitions beyond that on a dedicated system. However, Airboot fits entirely in the MBR rather than needing its own partition, and easily allowed adding a FreeBSD install, so it was a good choice.

Mind you, it could be worse, it could be Windows NT 3.51 - which sticks the boot files in a primary DOS FAT partition which also must be within the first 1024 cylinders. It doesn't tell you this, though, it just fails to boot after install with a less than helpful error message.

My other OS/2 system (after the Multiboot Warp 4 and Arca OS boxes) is a multi boot for DOS, NT 3.51, OS/2 1.3, OS/2 2.1 and Warp 3 (the 'old OS/2 and Ultima box'). OS/2 1.3 there does need to use the partition hiding feature, though.

Disk layout : […]
Show full quote

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.

This is a clever solution. If I understand this correctly the OS/2 Bootmanager can boot OS/2 from a logical drive, but for every other OS you have to boot the FAT16 Partition with dos and start the different OS through a bootmenu, right? Is it possible to add Win2k or WinXP in that Primary Partition? (Dos, NT4, Win9x, Win2k or XP Bootfiles on one single FAT16 partition?)

For Amithlon (amiga-OS 3.9) and every other linux this would work quite well, because you can boot them via "loadlin command" from dos, but what about BEOS (Intel), Rhapsody X86 and Nextstep (Intel)? I don't think that they will install in that circumstances.

I'm interested in Posting a problem that is not been discussed, how many replies do I need to submit before I can Post?

Whatever a single OS per partition is a bit like driving a bicycle with the stabilizer wheels 😉

You can have DOS/W31/95RTM/NT3.51/NT4 on a single FAT partition

You can have 95B-C or 98[se]/NT4/2000 on a single FAT32 partition (using the patched FAT driver for NT)

All you need to keep in account is the path of windows / programs /user profiles, but given those were already mostly different across various windows versions, half of the job is already done.

ynari wrote on 2026-10-02, 01:02:

No - it fails extremely early in the boot process, and even if the partition is low down in the hard drive sectors. I imagine to progress this it'd need to be disassembled, and it's really not on the list of projects I want to do any time soon.

Ontrack is useful, but the problem with all these adaptations (custom BIOSes such as XTIDE, Ontrack etc) is they work well with some operating systems/boot managers, and not with others. Boot Manager is definitely not ideal, but I understand where I stand with it, and it's possible to boot pretty much anything from it.

This is interesting because you mentioned translation, but I am not sure if this means that XTIDE uses a "non-standard" large disk geometry translation (which, if the case, I would ask : WHY??), or because of a generic bug within XTIDE (which I suppose is unlikely). Maybe you'd like to check if this still happens on a disk handled by XTIDE but that would not require any translation (e.g. configure it as a <512MB standard disk type).

There was pretty much two agreed standards for translating "large" disk geometry into DOS-valid CHS values, and practically every OS understands them, even today, so the popular DDOs are not usually a problem with era- operating systems. (Funnily enough recent Linux doesn't handle the Ontrack "shift the entire logical disk" approach, while older 2000s Linux had no problem with it).

ynari wrote on 2026-10-02, 01:02:

I haven't checked if ArcaOS has fixed this - from the looks of the install instructions it has, but my specific install starts with a 3.6GB boot, with other partitions beyond that on a dedicated system. However, Airboot fits entirely in the MBR rather than needing its own partition, and easily allowed adding a FreeBSD install, so it was a good choice.

Mind you, it could be worse, it could be Windows NT 3.51 - which sticks the boot files in a primary DOS FAT partition which also must be within the first 1024 cylinders. It doesn't tell you this, though, it just fails to boot after install with a less than helpful error message.

Oh I'm not complaining about OS2 BootMgr, it is my favourite boot manager right now (after GRUB4DOS, which is the only other one that I think is capable of directly booting OS/2, but for some reason I am not able to launch grub4dos in the pocket386).

dr.zeissler wrote on 2026-10-02, 06:30:

This is a clever solution. If I understand this correctly the OS/2 Bootmanager can boot OS/2 from a logical drive, but for every other OS you have to boot the FAT16 Partition with dos and start the different OS through a bootmenu, right? Is it possible to add Win2k or WinXP in that Primary Partition? (Dos, NT4, Win9x, Win2k or XP Bootfiles on one single FAT16 partition?)

For Amithlon (amiga-OS 3.9) and every other linux this would work quite well, because you can boot them via "loadlin command" from dos, but what about BEOS (Intel), Rhapsody X86 and Nextstep (Intel)? I don't think that they will install in that circumstances.

The 2k NTLDR at least can boot anything from 3.51 to 2K, and supports i13x, so it can go past the 1024 cylinder limit.
But basically, if you are doing one partition per OS, as long as that OS can be booted through its bootsector... you can put it in the OS/2 boot manager, I don't think you need the 2nd level bootloader, albeit certainly it will make things easier to install. (In fact, it's basically what the default install will do on its own?).

The Solutor wrote on 2026-10-02, 14:18:

Whatever a single OS per partition is a bit like driving a bicycle with the stabilizer wheels 😉
You can have DOS/W31/95RTM/NT3.51/NT4 on a single FAT partition

Well the problem is that you still need a boot manager for this configuration, so you're not really avoiding the discussions in this thread 😀

javispedro1 wrote on 2026-10-02, 17:55:

Well the problem is that you _still_ need a boot manager for this situation, so you're not really avoiding this particular problem.

Sure, but for all the MS installations a single boot manager from the newest of the installed OSes is more than enough

If OS2 (which is a bit picky and pretentious) is added to the mix the good old PQboot (from partition magic) handles easily it as well.

Exactly my point: with that you now have the same setup as the one described above with one NTLDR in the first FAT16 partition, and a 1st level boot manager for OS/2 and the others. You really gained nothing in terms of booting 😀

javispedro1 wrote on 2026-10-02, 18:03:

You really gained nothing in terms of booting 😀

You earn skill, experience and flexibility (I mean mental flexibility), which IMO is the point of such kind of experiments, given the practical use is pretty limited
You gain also storage space given partitions are inflexible while folders are much more manageable.