G‎reetings.
U r very welcome,i found it long ago,when I had troubles to replicate Live SD/CF versions,i also create these as gifts for friends & visitors,thus I am often replicating my Live FreeDOS+Windows 3.1+DOS & Win16 games compilation & I have to rebuild MBR in about 50% cases.
For now,i was always successful to make it bootable after rebuilding MBR,but 1ce manufacturers become aware,we have a workaround,they may do some countermeasure against our workaround,for example make MBR read-only or so,as they did,when tools for switching the Removable bit to Fixed appeared & then manufacturers made that bit read-only...
But for now...I had to rebuild MBR on about 15 SD/CF/flash drives/SSDs/HDDs(2 latter for another reason-MBR mods by previous OSs on 2nd hand drives had to be reverted)‎ & it always helped.
1 of my flash drives has no MBR,it is formatted as Superfloppy,fortunately bootable standard Superfloppy,but if it would be proprietary,I do not know,if rebuilding MBR would help in this particular case.
I guess,U will be successful with most of Your flash drives.
& I never had seen in flash drive specs details about their MBRs,or do they even have them or r those Superfloppies(very rare),in specs U just find parameters as read/write speeds,capacity,cache,maybe sometimes file system,but U always may change the file system(& U must do so,if there is ExFAT & U wish to install FreeDOS,U must convert it to FAT32),but MBR parameters never mentioned.
& U can run into proprietary MBR also on a premium drive,it is not about cheap or expensive,that is not a quality parameter,that is a manufacturer's policy/strategy parameter‎,not necessarily related to targeted economical class,thus the price is sure not a reliable distinguishing factor to avoid proprietary MBRs.
The tested vendor factor is more reliable,for example if Verbatim brand worked for U,it will most probably continue to work...until a company decides to change their policies,or is bought by other company with other policies...
With regards Sabina Zelená.
Live long & prosper.
Sent from my BlackBerry Passport,RIM OS 10 smartphone named <b>Uhura</b> after deceased Star Trek actress Nichelle Nichols.
<b><font color="darkgreen">With regards Sabina Zelená[=Green].
LIVE LONG & PROSPER,live & let live=DO NOT EAT,NOR WEAR ANIMALS,nor do not pay Their Murderers & oppressors,please.
Shalom/Peace/Shanti/Mier/Nyugalom.</b>
Ethical food for Cats,Dogs,& humans:
VeganStore.cz
AmiPetFood.com
Y U should not eat,nor feed Animal products to others:
NationEarth.com
Realita.tv
About Kosher rules beings updated:
JewishVeg.org
Prečo by ste nemali žrať nevinné Zvieratá,ani Nimi nikoho kŕmiť:
soucitne.cz
svobodazvirat.cz
ohz.cz
vegspol.cz
Infinite diversity in infinite combinations is worth protecting & respecting...
Veganism is the base of Vulcan Wisdom.
...
From: Thomas Desi via Freedos-user
Sent: Friday, February 13, 2026 14:47.‎
To: Discussion and general questions about FreeDOS.
Cc: Thomas Desi.‎
Subject: Re: [Freedos-user] Fix mbr?

cool info on the MBR. Thanks so much!

(would be good to know more about the usb tech specifications BEFORE buying that cheap stuff)

prosper FreeDOS!
Thomas

Am 13.02.2026 um 14:25 schrieb Sabina Zelená. via Freedos-user <[email protected]>:

G‎reetings.
Yes,Rufus is good for installing FreeDOS to a flash drive/CF/SD card,etc.,it contains FreeDOS,but some RDDs(flash drives/SDs/CFs) r not made successfully bootable by Rufus because of a proprietary MBR from the flash drive manufacturer,often designed exactly against making the drive bootable,in this cases U must rebuild the terget drive's MBR & may be totally impossible,if the target drive is Superfloppy with proprietary boot sector incompatible for standard bootstrap.
Usually rebuilding MBR fixes the drive to be able to be bootable,i had success with Partition Guru for DOS,not very successful doing so via Windows.
But those "some USB sticks" the problem is definitely a proprietary MBR,which must be rebuilt.
Live long & prosper.
Sent from my BlackBerry Passport,RIM OS 10 smartphone named <b>Uhura</b> after deceased Star Trek actress Nichelle Nichols.
<b><font color="darkgreen">With regards Sabina Zelená[=Green].
LIVE LONG & PROSPER,live & let live=DO NOT EAT,NOR WEAR ANIMALS,nor do not pay Their Murderers & oppressors,please.
Shabbat Shalom/Peace/Shanti/Mier/Nyugalom.</b>.‎
From: Thomas Desi via Freedos-user
Sent: Friday, February 13, 2026 10:50.‎
To: Discussion and general questions about FreeDOS.
Cc: Thomas Desi‎.
Subject: Re: [Freedos-user] Fix mbr?‎

RUFUS is s good tool to format and boot FreeDOS from USB. 
Some USB Sticks DON’T work. I have no idea why. 
Try also different partitionings (in RUFUS possible)
For me VERBATIM USB sticks always work.
I can boot from one (C:) and have a second also attached, which becomes D:, both work.

I had a bunch fo cheap sticks, FreeDOS doesn’t even recognise. 

good luck
Thomas

Am 12.02.2026 um 20:10 schrieb Jakob Stengård via Freedos-user <[email protected]>:

So i installed freedos on a pre-formated compact flash card.
As it turns out, the computer won't boot from the drive.

Now, i have re-formated the drive and put all the files back.
Can use some command on the boot disk to just write the MBR,
or do i need to run setup.bat and will that work?

I don't want to run all of the installer again, that took 3 hours last time.

Many thanks.
--

Med vänlig hälsning (Best Regards)
Jakob Stengård
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