[syslinux] Question of syslinux chainloading

Adan Calderon adancalderon at gmail.com
Fri Apr 19 08:43:08 PDT 2019

Glad the boot sector method works for you.  It's what I use.  I typically
first make the USB Bootable with DOS and then backup the sector and install
syslinux.  There is a windows tool that makes this really easy.  Also there
are several versions of ms dos 7 's io.sys. There were some patches
released by Microsoft.  My USB pen drive is 64 gigs and fat 32.  When I
select to Boot from DOS it comes out as drive C.  I have a collection of
tools mostly related to BIOS flashing and such.


On Fri, Apr 19, 2019, 11:05 AM Lu Wei via Syslinux <syslinux at syslinux.org

> On 2019-4-13 8:45, Lu Wei wrote:
> > On 2019-4-13 4:23, C. Masloch via Syslinux wrote:
> >> MS-DOS 7.10 (first appearing in MSW 95 OSR2, later re-used in MSW 98
> >> and 98 SE) and 8.00 (MSW Me, and MSW XP DOS boot diskettes) both
> >> support FAT32 equally well.
> >>
> >> MS-DOS 8.00 (without some patches that are around) only supports
> >> booting in DOS mode from diskettes. Hard disk booting only succeeds
> >> when directly passing control to the Windows loader.
> >>
> > Rufus can only extract DOS8 files from my WindowsXP. I also tried
> > HPUSBFW, which can specify DOS files location, so I used it to create
> > DOS7 and DOS8 USB boot disk (on the same USB-HDD, after Rufus
> > experiment, only io.sys and command.com), and the result is the same:
> > DOS8 can boot while DOS7 failed. Even simply copying DOS8 files to DOS7
> > formatted disk (I hope it excludes bootsector incompatibility) can make
> > it bootable. So I think DOS8 may be better with FAT32. The Disk is 8G.
> >
> You are right! After further reading and experiment, I found that the
> dos7 file IO.sys I used is the culprit: after being replaced by a "good"
> file, dos7 can boot normally (before syslinux). After comparison I found
> it was cut short, missing some padding zeros. That file behaved well
> until failed under this specific situation, which is odd. But after
> syslinux, that good IO.sys still cannot make "com32 chain.c32 boot
> msdos7=io.sys" work.
> MSDOS booting through syslinux also solved: it turns out the boot sector
> file should be from the original, not the one I copied from another
> system or by bootpart tool. I saved a dos.bs file when the usb-hd could
> boot to DOS, then after running syslinux, "boot dos.bs" works. ("bss
> dos.bs" works too; "com32 chain.c32 boot file=dos.bs" works with a
> warning about mapping; "com32 chain.c32 boot msdos7=dos.bs" do not work.)
> The dos.bs file is saved by HxD. I tried to get one by copybs.com, but
> failed with the message:"Error:Filesystem not found on disk" (missing a
> Blank after "File"). Maybe it only supports floppy disk.
> So basically the problem is solved, although I think there are some bugs
> or improvements in the copybs and boot sector handling (I thought those
> mysterious options like setbpb, will make any dos7 bs file work). I hope
> the information here could be useful to some developer. Thank all of you
> who give suggestions, especially Ady.
> --
> Regards,
> Lu Wei
> IM:     xmpp:luweitest at riotcat.org
> PGP:    0xA12FEF7592CCE1EA
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