On Sat, Jul 9, 2016 at 3:12 AM, Ulrich Hansen <my.gr...@mailbox.org> wrote:
> Am 09.07.2016 um 02:22 schrieb Rugxulo <rugx...@gmail.com>:
> Using VHD instead of VDI has the advantage that it can be mounted in Windows
> and other systems.
> What other systems support VHD? Are there different versions (besides VHDX)?
> You can mount the image in Windows, OS X and GNU/Linux.
> That just means you can open the virtual FreeDOS drive C:\ in Windows
> Explorer, Finder or Nautilus.
> It doesn’t mean that it runs with other virtualization software.

Pardon any temporary confusion on my part. I can't remember every
little detail, even though I've superficially read up on some of it. I
haven't personally tested every combination, which is more direct
concrete knowledge.

> Hmmm, I don't see any mention of "vhd" in qemu-img --help. And yet one
> random page says it supports "vhdx". Eh? Do they just call it "vpc"
> instead? Apparently so. (qemu-img does mention "vpc“.)
> No. VHD has nothing to do with qemu. You can convert it though with
> "qemu-img" or with "VBoxManage clonehd“.

No, I meant that qemu-img can create .vhd (although I now see that
even Win7 can "create" or "attach" as well). But the
"qemu-img"-created .vhd didn't work for me. Win7 says, "Virtual Disk
Manager: The version does not support this version of the file format"
(which is bad news), and I don't know exactly why. (I don't know how
to competently compare them or check the versions.) So I had to create
.vhd with Win7 itself (which also quick-formats for me, which is

I would consider this a bug or unfortunate compatibility quirk, which
is exactly the kind of thing I was worried about. Some naive person
will use "qemu-img create" for .vhd, but (unbeknownst to them) it
won't be supported by Win7.

(BTW, I had briefly read about this "Win7 attach" method months ago,
even mentioned it to Eric Auer in private email, but I had never
bothered to try it. Of course, I don't have any .vhd files and never
used VPC, so I didn't majorly care. I didn't think too hard about
inserting files.)

BTW, just so I'm clear, the Win7-created .vhd does work fine with QEMU
2.6.0 (Win64 version from http://qemu.weilnetz.de ). I was also able
to extract a file successfully (matching CRC32) with either 7-Zip's 7z
[sic] or Explorer.

> Most people who are using FreeDOS in VirtualBox run Windows as host. Giving
> them the possibility to mount the FreeDOS disk C:\ to get their work into
> FreeDOS or out of it, seems like good idea.

But Windows doesn't come with any emulator / hypervisor. Sure, some
enterprise-y editions of Win7 had VPC and "XP Mode", but end users
didn't get that. (But Win8 never cared for offering that further,
AFAIK.) Also, last I heard, Hyper-V was Win8 64-bit Pro VT-X only. So
that too is out of reach for normal consumers.

What I prefer these days is (third-party) VBox and QEMU / KVM.
Admittedly usually using Windows host, but sometimes I try under Linux

> But I will keep the VDI updated and available on the website too. So 
> everybody has a choice.

It may be too much stress to maintain various images (different
formats but identical contents). It also may be impossible to have one
image format supported by all tools. Maybe "raw" is best for ultimate
compatibility (but of course that wastes space if not all used,
although it may be faster overall). Maybe use "raw" until finished /
finalized, then convert to a better, space-saving format.

Out of curiosity, I'm downloading your "FreeDOS1.1.vhd.zip" (33 MB but
98 MB unpacked). Seems to only use 84 MB out of 4 GB total free
(FAT32). BTW, my native FAT32 partition (4 GB) is almost full.   ;-)
 Most of that (1+ GB) is lots of different versions of DJGPP stuff,
though, so not mandatory by any stretch.

> So I'm not fully convinced (yet) that there is one portable, neutral
> format that will work across most emulators.
> Me neither. VMDK might be a candidate. It is also fully supported by
> VirtualBox. And there even seems to be a vmware utility to mount the VMDK
> file as disk.
> Unfortunately this software is quite old and no longer supported so I am not
> sure about it.

There was some old (32-bit only) driver for manipulating one format,
but it was also discontinued. So yeah, it's hard to even partially
rely on something that doesn't universally work for all use cases.

BTW, I had considered a 512 MB FAT16 to be reasonable size for average
redistribution. But "qemu-img create -f vpc metahd.vpc 512M" actually
creates a little beyond what I expected. So it's better to use "510M"
in order to keep 8 kb clusters. Anything bigger (e.g. 16 kb) is very
wasteful, IMHO, and not worth using. I think it's probably better
overall to have two (or more) 510 MB FAT16 partitions (8 kb clusters)
as separate drives rather than one big drive wasting space with dopey
16 kb clusters. I had learned that lesson the hard way in the old days
on my old P166. Probably irrelevant to you, but I'm just mentioning it
for completeness.

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