mbldr (Master Boot LoaDeR)

Logo of mbldr

Table of contents:

  1. News
  2. Summary
  3. License
  4. Documentation
  5. Screenshots
  6. Features
  7. Download
  8. ToDo
  9. Help needed
  10. Translation status
  11. Building instructions
  12. Contacts
  13. Links


September 30, 2009
At this point I see no other useful features that can be added to mbldr. MBR sector is almost full, the code seems to self-sufficient, stable and rock-solid. If you have any ideas, bug reports, questions or comments feel free to contact me using forum. The project is now in maintenance mode which means I will help users and get back to development if there are new interesting features to add. I would also be happy if somebody is interested to participate in development or interface translation to other languages. Stay tuned, mbldr is surely not dead - it is obviously still in the zone of my interest. At the time being I don't expect new releases in the nearest future.

December 12, 2008
mbldr 1.46 has been released. New chainload feature (refer to FAQ section, question #13), fix of hanging with timer interrupt, Czech translation, "restore from backup" changes.

May 30, 2008
mbldr 1.45 has been released. Boot-timer fix, French translation, partitions hiding/not hiding, few other improvements.

December 19, 2007
Mbldr sources are now available in Subversion repository on Sourceforge. Use "svn co https://mbldr.svn.sourceforge.net/svnroot/mbldr mbldr" command to get the source tree. Initial version in Subversion corresponds to mbldr-1.44, I have not added earlier versions.

November 29, 2007
I posted new open position to "Help wanted" section on the sf.net web-site. It asks for new translations.

November 23, 2007
mbldr version 1.44 has been released. It introduces multilanguage interface (only Russian translation is available now).

June 6, 2007
mbldr version 1.43 has been released. It introduces new GUI configuration program.

January 11, 2007
mbldr version 1.42 has been released (changes are only in Windows version of installation program).

November 29, 2006
mbldr version 1.41 has been released. It introduces the support of Microsoft Windows Vista.

November 15, 2006
mbldr version 1.40 has been released. It contains no code developed by Thomas Wolfram anymore, so the project is now totally covered with BSD license. The only significant difference is that I have removed the line "All advertising materials mentioning features or use of this software must display the following acknowledgement: This product includes software developed by Thomas Wolfram."

October 31, 2006
mbldr version 1.39 has been released

August 18, 2006
mbldr version 1.38 has been released

June 13, 2006
mbldr version 1.37 has been released

March 10, 2006
mbldr version 1.36 has been released



mbldr is yet another boot loader which fits into first sector of an HDD (MBR). It allows to choose which partition to boot and is intended to replace an MBR coming with DOS/Windows (fdisk /mbr). It may boot OSes above 1024cyl, Linux/BSD are also supported. mbldr is based on OS Boot Select (OS-BS) by Thomas wolfRAM (see below).
mbldr is not an operating system loader. I can not boot Linux or Windows directly (thus it is not a replacement of LILO for example), but it can boot appropriate loader from a boot record of a particular partition (again LILO or GRUB for instance).
mbldr can be installed and configured using special tool. Before version 1.43 there was only one choice: to use a command-line installation tool which supports DOS (MS-DOS, FreeDOS, etc.), Windows 98/ME, Windows 2000/XP/Vista, Linux and BSD-flavours (FreeBSD, OpenBSD and NetBSD). Now it is also possible to use graphic version of this tool. It uses wxWidgets toolkit and supports Windows 2000/XP/Vista, Linux and BSD (DOS and Windows 98/ME are not supported, you need to use command-line version).


Current mbldr project is a successor of relatively old project named OS-BS (OS Boot Select) written by Thomas Wolfram. Its homepage seems to be lost now. I have found a copy of these pages thanks to excellent Web archive engine.
That project had at least two official versions: 1.35 and 2.0b8. Since both are very old (the latest is dated October, 1993) and then the project evolved into commercial System Selector described at BootManager website, I have decided to continue the open source development. However you may download older versions of OS-BS at BootManager or FreeBSD FTP sites.
As a starting point of my development I have decided to use 1.35 release of OS-BS by Thomas Wolfram because it fits into 1 sector. Version 2.0 uses more than 1 sector what is not my goal. Since I use different tricks to fit into MBR, newer versions of mbldr WILL BE INCOMPATIBLE with OS-BS releases by Thomas (against his recommendation in the source code). However I believe it would not lead to problems since it is always possible just to reinstall the bootloader from scratch. The uninstallation of the boot loader is very simple. You may use a special menu item in the installation program pointing it to a previously stored MBR. The another way is to use programs like "fdisk /mbr" under MS-DOS. The original releases of this software were included into the distribution of a FreeBSD (see /tools directory, for example in release 5.4) and I believe it was tested thoroughly enough. I hope at some point the updated versions will be included into FreeBSD distribution as well.

Project name

I have contacted Thomas by e-mail and asked him whether I may continue the development using the same project name, but he denied it. This is because some software publishing company owns "OS-BS" name. Since I definitely want to avoid legal issues that was the reason why the name has been changed to "mbldr". In addition, Thomas insisted keeping his license with no changes (I would like to use BSD license). From the version 1.40 all code written by Thomas is eliminated, so at the time being mbldr is fully covered with BSD license. Below here are our e-mails related to this topic:


I'm sorry. I do not allow to use the name OS-BS for
an open source project or any other purpose. Also
I do not allow redistribution of my source code under
any other copyright or license terms than my own.

It is not possible for me.

The software OS-BS has become a commercial product since
1997 and is sold in several versions in Germany, France,
Spain and elsewhere. It has evolved much since the
early 1.x and 2.x versions.
The rights are hold by a large software publishing house
and I continue development of the product for them.

Thomas Wolfram

> -----Original Message-----
> From: Arnold Shade
> Sent: Tuesday, March 07, 2006 4:45 PM
> To: Thomas Wolfram
> Subject: OS-BS
> Hello,
> My name is Arnold Shade. I have found your nice program called OS-BS in /tools directory
> on one of FreeBSD distribution disks. It's really nice, but since it seems you are not
> supporting it now (2.0b8 release was done in October 1993), I would like to continue
> open-source development of this program.
> [ ... skip ... ]
> As a starting point of my development I have decided to use 1.35 release of OS-BS
> because it fits into 1 sector. Version 2.0 uses more than 1 sector what is not my goal.
> As far as I understand you tried to evolve OS-BS to commercially
> available software available at http://www.bootmanager.com/
> Thus, my question is: Do you allow the existence of successor of OS-BS? May I be current
> maintainer? May I use BSD license for it? May I create an appropriate project of
> sourceforge and publish all the details there? I promise to leave current name without
> modifications (OS-BS) and write your name wherever acceptable (README files, about boxes,
> web-site, etc.) However your signature ("wolfRAM") will be lost in MBR and I will break
> the compatibility with older versions (location of some data structures in MBR will be
> changed) because I'm optimizing the code much.
> Thank you in advance.
> Best regards,
> Arnold Shade

Project goals

What probably never will be a goal

I have no plans to support all unnecessary (from my point of view) features listed below in future (there is no space in MBR to locate a complex code):


The initial license and copyright that were included in OS-BS by Thomas Wolfram are now not used since mbldr currently contains no code inherited from OS-BS. At the time being (since version 1.40) mbldr is fully covered with BSD license.

Copyright (c) 2006-2008, Arnold Shade
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright notice,
  this list of conditions and the following disclaimer in the documentation
  and/or other materials provided with the distribution.
* Neither the name of Arnold Shade nor the names of contributors may be used
  to endorse or promote products derived from this software without specific
  prior written permission.


Every new piece of code (patches, fixes, improvements, etc.) submitted for inclusion into mbldr should satisfy the license shown above.



  1. So-called IBM PC-compatible computer with Intel 386 architecture CPU is required. It will not run on Sun Sparc or PowerPC-based Macintosh.
  2. Relatively modern BIOS that allows to use new functions of interrupt 13h for loading/saving sectors (in order to support booting from >1024cyl). Mbldr is incompatible with older BIOSes (even when booting operating systems below 1024cyl)
  3. The CLI version of installation/configuration program could be compiled and run under MS-DOS/FreeDOS, Windows 98/ME, Windows 2000/XP/Vista, Linux and BSD. GUI version supports Windows 2000/XP/Vista, Linux and BSD (DOS and old Windows-family are not supported), it requires wxWidgets development toolkit for building. DOS version requires DPMI interface (it also works under Windows 98 or ME in DOS-emulation mode). DOS version does not work under NT-family of Windows in DOS emulation mode, you need to use special version for Windows 2000/XP/Vista.

Installation, uninstallation and configuration

The mbldr project is intended to be used by advanced users on their desktop computers. If you have several operating systems and want to be able to boot either of them, you may use mbldr. It is a replacement of the default boot loader in MBR which for instance could be written there by Microsoft Windows installation.
The instruction below addresses CLI version of installation/configuration utility running under MS-DOS or FreeDOS (other versions are very close to what is described here for DOS):
  1. Download .zip archive with a binary corresponding to the latest release of mbldr
  2. Unzip the contents of the archive to some directory on a hard drive. The directory should be located on a partition accessible by DOS, i.e. it should be either FAT or FAT32. You may also copy it on a floppy or a CD.
  3. Download and unzip the contents of DPMI server. If you are using CWS DPMI, make sure that CWS executables are located either in the same directory as mbldr executable or in a directory listed in PATH environment variable (under Windows 98/ME you don't need DPMI engine)
  4. If you are running Windows NT-based operating system (2000/XP/Vista) reboot from DOS-bootable floppy. El-torito CD could be used as well. Under Windows 98/ME you may use DOS-emulation box without rebooting into DOS. (of course you do not need this step if you are using Windows 2000/XP/Vista version of installation program)
  5. Run "mbldr.exe -h" to get command line help (in Windows 2000/XP/Vista or Linux/BSD name of the command-line executable is mbldrcli)
  6. Run "mbldr.exe" (mbldr.com for very old versions) to enter interactive configuration mode (you may need to specify device name to manage under Linux or BSD with the help of -d command-line switch, however autodetection is supposed to be working properly)
  7. The navigation through menus is done with command-like interface. You should read a list of bullets, make a choice and then type the appropriate symbol (usually a digit or a lower-case letter, but could also require typing numbers and labels) and then press <Enter> to confirm.
  8. Use special boot menu item "Skip boot" if you want to instruct BIOS to try another boot device. Mbldr calls int 18h what usually leads either to network boot or CD-ROM boot (depending on a boot sequence configured in BIOS).
  9. Use special boot menu item "Try next hard disk" if you want to load MBR from a next hard disk (increasing BIOS device number: the first is 80h, then 81h, etc.). Please note that this option is dangerous and may lead to data corruption. If configured improperly your MBR may be mistakenly overwritten by other boot managers. Use with caution and thoroughly read the following warning: New master boot loader gets a number of drive being used as a parameter. Theoretically this scheme should work fine assuming that all boot loaders respect this input parameter. Unfortunately several boot loaders ignore it assuming that the drive number used to boot is always 0x80 (what is incorrect according to EDD3 specification). It may lead to impossibility to boot for so called "passive" master boot loaders (that just try to boot not updating MBR each time). But even worse for so called "active" master boot loaders (that modify MBR each time you boot) you may overwrite MBR on the wrong disk. Please note that "Next HDD" feature is not the same as the one provided by BIOS (boot from either of installed hard disks). BIOS does the renumbering of hard drives making bootable disk always 0x80, while mbldr does not. Use this feature at your own risk! It is dangerous and may lead to data loss if you have master boot loaders others than mbldr with version 1.37 or above! However I have tried following combinations successfully: mbldr+mbldr, mbldr+LILO, mbldr+GRUB, mbldr+standard MBR from DOS/Windows. Any others probably don't work, in particular mbldr136 and os-bs. Use this feature at your own risk, it's DANGEROUS!
  10. You always may use 'q' to immediately quit from a program without saving any changes. Also try Ctrl-C if something goes wrong.
  11. Before making any changes on your hard disk the program will ask for a confirmation
  12. Always do a backup of the old MBR. Better to store this file somewhere on a bootable floppy or El-torito CD together with appropriate version of mbldr installer. Please note that uninstallation of mbldr is impossible if you have not saved the backup copy of MBR first.
  13. The length of particular label for a bootable partition is not limited. Only total number of characters used for boot menu makes sense. You will get a warning when you exceed it.
  14. Don't use non-standard native charsets when typing labels. Even if they are visible at the time of configuration these symbols are not yet available at boot time. Instead you will see unreadable sequence of pseudographic characters garbling the display.
  15. Please note that mbldr overwrites MBR not only at the time of installation but as well each time you boot (setting "active" flag for current partition and hiding inactive FAT/NTFS partitions). You have to switch off MBR boot-virus protection in BIOS in order to boot correctly
  16. Mbldr installation program does not modify the partition table in MBR (except restoration from backup) thus it is not mandatory to reboot after you have installed mbldr
  17. When restoring from a backup mbldr recognizes if the partition table has been changed. It could be a moved "active" flag but also a real different partition table (you are informed about that). Here you have two options: full overwriting of existing MBR with a backup file (could be dangerous since an out-of-date table may be restored, but useful if your master boot sector is destroyed) or restoring only the master boot loader program keeping partition table untouched.

For Linux or BSD you deal with tar.bz2 archive, you need to compile the program using Makefile.unix and you need to be root in order to run the installation (this is because you are modifying disk directly using something like /dev/hda). For Windows and Linux/BSD all DPMI-related stuff is not needed, file-system type restrictions are also not applied. Please take in account that you have to properly reconfigure your main boot-loader (like LILO) to avoid conflicts with mbldr and allow them to coexist.

To avoid an inconsistent state of MBR contents it is necessary to reconfigure mbldr each time you move any of the bootable partitions (for example with a help of PartitionMagic). Resizing operation (without movement) of bootable partitions does not affect mbldr internal tables. Movement, deletion etc. of non-bootable partitions also does not affect the configuration of mbldr.

Note: the active id does not have its usual meaning to mbldr. "Active" is only a flag in the partition table that may be analyzed by respective operating system. Mbldr sets it to appropriate primary partition marking the OS as "active" at boot time. Logical drives are never marked as "active". Hiding of logical drives is also not performed.

"fdisk /mbr" doesn't affect the partition table. It puts only an ordinary master boot program back. This is another way to uninstall mbldr. But please note that there are some differences in the master boot loaders placed by different operating systems, so be careful. For example, if you call "fdisk /mbr" from MS-DOS 7.1 (part of Windows 98/ME) MBR is initialized with a boot code that is unable to boot operating system above 1024cyl.

If you are unfamiliar with mbldr yet and don't like command line, it is suggested to begin with GUI version (mbldrgui.exe under Windows 2000/XP/Vista), take a look on screenshots section.

Frequently asked questions (FAQ)

Q1: Yet another boot manager? What are the advantages of mbldr over others?
A1: If you want a boot manager which is not bound to any of operating systems you have installed - mbldr is at your service. It will not fail to boot your secondary operating system if you completely destroy the primary. Consider a situation when you have 2 primary partitions: one with Windows XP and another one with Linux. What are options to boot either of them? Using LILO which is able to boot both OSes you will loose an ability to normally boot a system to Windows XP if you completely fill Linux partition by zeroes. The same with standard Windows loader + loadlin executable. In this case you should not break Windows partition otherwise you will loose an ability to load Linux. Of course there are many other third-party managers which are not parts of the operating systems above. Several alternatives to mbldr are listed in Links section. However almost all of them require either separate partition (like OS/2 boot manager) or a directory in FAT partition (like PQBoot) or occupy almost the whole track #0 on cylinder #0 (it is unused on most systems). mbldr requires only the space which is reserved for the master boot loader by definition, only 446 bytes of 1st sector are used. Nevertheless there are some drawbacks: simplicity leads to low quality of user interface (only text with minimum usability), less features could be included: no partitions autosearch and password protection, there are other problems as well.

Q2: I have set up mbldr and then booted my Windows XP. But it accidentally shown me a dialog with something like that: "New hardware has been found. Would you like to reboot?" What is this all about?
A2: At the time of Windows installation MBR is updated with the boot loader and 4 bytes presenting a DiskSignature (or so-called NT Driver Serial Number) of a hard drive which is issued by Windows installer. Installation of mbldr overwrites these bytes. Most probably it leads Windows to redetect and possibly enumerate partitions on this HDD what causes updating of internal hardware database. As a result of that you see this dialog. I believe it could be safely ignored (just press "No" there) since no actual changes have happened in system's hardware. This applies to mbldr 1.40 and below, all newer versions should keep DiskSignature untouched.

Q3: When I run mbldr.exe I see "Load error: no DPMI - get csdpmi*b.zip", what should I do?
A3: It seems you are running mbldr.exe in a pure DOS environment. You need to get DPMS extender in order to run mbldr.exe. You may use free CWS DPMI server (redistributable under the GPL). Release 5 of CWS DPMI could be found at ftp.delorie.com or here is a local copy. Unpack binaries to the same directory where mbldr.exe is stored and run it once again.

Q4: When I run mbldr.exe I see "Warning: cannot open swap file c:\cwsdpmi.swp" but then the execution continues. Is there something wrong with it?
A4: You may safely ignore this warning produced by CWS DPMI server. Usually it happens when no disk C: is found in a system (for instance all FAT/FAT32 drives are hidden or disk is not yet partitioned). Since mbldr does not require too much memory swap is not needed in general.

Q5: When I try to boot one of my operating systems the boot menu just redraws itself ignoring boot attempt. What is going wrong and how to boot my OS?
A5: There are at least two reasons that may cause this issue. One of them is that you have moved (or deleted and then created in another place) the partition with the operating system you want to boot. In this case you have to reconfigure mbldr (delete the entry marked as "[!!!BROKEN!!!]" and then add it once again). The another reason of this problem maybe in the limitation of BIOS. For example some motherboards don't detect hard disks bigger than 128Gb. This limitation is also applied to BIOS EDD3 calls (enhanced int 13h) therefore you cannot load boot record of a partition above this boundary. Anyway the common explanation of boot menu reappearance is either an error of BR sector reading or an absence of 0x55AA magic number at the end of sector being read.

Q6: Compilation breaks with "error: argument to ORG should be numeric" message in mbldr.err. What am I doing wrong?
A6: Till mbldr 1.44 the version of nasm required for building was greater or equal to 0.98.36. Release .35 which is often shipped in many popular (but rather old) distributions could not be used. Please note that starting on version 1.45 of mbldr nasm 2.x. is required.

Q7: When trying to update the MBR contents on /dev/ad0 under BSD I get "Operation not permitted" error. How to overcome this?
A7: This protection of BSD is active because hard disk is available for writing at the moment. Try to issue a command "sysctl kern.geom.debugflags=16" to temporarily disable it. Update your MBR and then return this value back to 0.

Q8: I am using two items in my boot menu: "1. Windows XP" and "2. Skip boot". I have configured the default menu item to be the last OS I booted to. So I expect "Skip boot" should be the default one after I tried to use it once. But it seems that mbldr always boots Windows XP. Why?
A8: "Skip boot" and "Next hard disk" are special boot menu items that are associated neither with particular partition nor with an operating system. They are not remembered as default boot menu items unlike usual partitions. However you may still mark them as default ones manually.

Q9: I had 2 hard disks in my PC, both have Windows XP installed, I used dual boot with the help of NTLDR. When I switched off first HDD, second one did not boot alone. I installed mbldr onto a second hard disk but when I choose the item in boot menu system just hangs. How to boot second Windows without my first hard disk?
A9: This is not a problem of mbldr, you need to reconfigure Windows boot loader in order to boot properly. When you installed second Windows on the old PC configuration (with two hard disks), Windows installer has configured the existing boot loader on the first HDD. Both MBR and boot record on the second HDD was left intact. So, after you removed the first HDD system was unable to boot and it is expected. In addition to installation of mbldr on the second hard disk you should repair Windows loader in first sector of a bootable partition. It could be done via system recovery console. Please refer to How to use fixboot, Why Windows XP does not boot (Problem #6) and Recovery console overview

Q10: I have one hard disk with 3 primary partition: one for Windows, one for my personal data and one for a backup image of Windows. I used mbldr so I can be able to boot Windows or restore the image. The problem is that when I use mbldr partitions 2 and 3 become hidden including partition 2 which contains my personal data.
A10: You are right, mbldr can hide all other primary FAT/NTFS partitions when booting either of configured operating systems. So, in your case partitions 2 and 3 are hidden and it is expected behavior. You can disable partitions hiding if you want to (this is a global setting, not applicable for individual partitions). You may also convert your primary partition #2 into logical disk on extended partition - this will let you to aviod hiding of this particular partition (please note that conversion operation may cause data loss). Also please note that if you are using Windows 2000/XP (not 98/ME) as your main operating system, you may ask it to access hidden primary partitions in the same manner as for visible ones. Go to Start->Settings->Control_Panel->Administrative_Tools->Computer_Management. There you should choose Disk_Management in the Storage tree branch and use Change_Drive_Letter_and_Path item in context menu on a desired partition. Unfortunately Windows 98/ME do not support this.

Q11: I have plugged second hard disk to my home PC. My main HDD has mbldr installed, but second one also contains Windows operating system (no mbldr there). I wanted to reconfigure mbldr in a way to add one more option for booting from another HDD but this feature does not function properly. Windows on second HDD is not booted at all while all others remain ok. How can I boot an operating system from second hard disk?
A11: This is true, sometimes "Try to boot from next hard disk" option does not result in normal boot of operating systems on any HDD except the first one. This is not because of improper functioning of the mbldr code in MBR, but mainly because of bad implementation of OS-specific boot-loaders (like ntldr). The workaround in this case could be the following: instead of using "Try to boot from next hard disk" try "Skip boot attempt and try another device" menu option. In this case you need of course to adjust the settings in your BIOS accordingly - your first HDD should be first boot-device, your second HDD should be the second (floppies, network boot and CD-ROM boot should be below hard disks). You probably also need to check another BIOS option called like "Boot other device" or "Try other boot devices" to disable the limitation of booting only from the first configured device (first HDD in our scenario) - it is usually located near the definition of boot devices priority.

Q12: What is the difference between system and user timers in the section of timed boot configuration?
A12: The main and most reliable way to configure timed boot is to use so-called "user timer" which corresponds to interrupt 1Ch. But unfortunately some buggy BIOSes (mainly on modern laptops) do not call this interrupt causing timer in mbldr to stand in idle. If you experience problems with timed boot while all other methods work fine (immediate boot, boot by request typing a key, etc.) try to change the timer from "user" to "system" in mbldr configuration.

Q13: How can I use chainload feature?
A13: This feature is inspired by forum thread about TrueCrypt, where it was suggested to allow mbldr to coexist with other software which occupies MBR. So, typical scenario includes installation mbldr after the software like TrueCrypt, saving the contents of MBR to another sector (safest way is to use one of empty sectors from first track on first cylinder). As mbldr allows to backup and restore MBR to/from any sector or a file you are free to manage the contents of any sector you need without other tools. So, the example with TrueCrypt is: install TrueCrypt in full-disk encryption mode (this affects MBR), boot Windows, run mbldr installation/configuration tool, save current contents of MBR (including partition table of course) to one of the empty sectors on first track (mbldr provides you with a list of empty sectors), add chainload entry to the list of bootable entries. You may need to disable partitions hiding and disable marking bootable primary partition as active to let TrueCrypt copy of MBR think it resides in MBR (otherwise it informs you about differences in partition tables). Please note that every time you move, create, delete or resize partition you need to resync partition table between actual MBR and chainloaded copy.

Useful hints and advices

Important notices and limitations

There are following limitations and configurations that have never been tested yet. All information related to the topics below is welcome (test cases, links to appropriate documentation, patches, etc.)

Known issues

Here is a list of already known but still unresolved issues and problems in the current release:
  1. mbldr does not work with VMware ESX operating system
  2. Mbldr can not be compiled with nasm 2.04 and 2.05, need to downgrade nasm to version 2.03.01 or earlier
  3. Mbldr 1.45 may hang during boot if system timer is enabled. This is a bug in timer interrupt handling routine, fixed in 1.46. If you experience issues with such hanging, try user-timer option or roll-back to 1.44. You can also try newer versions like mbldr 1.46.
  4. It has been reported that mbldr configuration program for DOS hangs at the stage of hard disks detection. The known configuration is one of the modern (as of end of 2008) motherboards with Intel CoreDuo CPU and PATA devices. The workaround for this problem is to use mbldr under Linux or Windows. However detailed reports of similar issues are welcome (not yet fixed as of mbldr 1.46).
Please feel free to report any bugs you have found. I'll try to fix them as soon as I can.


If mbldr does not work for some reason you may ask for support. What do you need to provide in order to get help:
  1. Run the program with "-v" command line switch and send me a log file
  2. Do a screenshot of a problematic menu (if the problem is in configuration program)
  3. Send me an explanation of sequence of steps (in particular what you type in configuration program)
  4. Describe hardware configuration (disks subsystem: number of drives, their types (ATA, SATA, etc.), primary or secondary, sizes, etc.)
  5. Report OS version where you execute mbldr configuration program
  6. Report the version of mbldr you are using
  7. Explain the problem (crash, hanging, incorrect behavior, etc.)
  8. Send me a file with custom boot menu text if you use it
  9. Describe partitioning scheme of your hard drives (sizes and filesystems on primary partitions and logical disks). Appropriate screenshots of fdisk or PQMagic may help as well.
  10. Provide a description of OSes you want to boot: where are they, how many oses you want to boot, what are they (brands+versions)
  11. What other boot-related software do you use (other boot managers for example on other hard disk, OS loaders like LILO, etc.)
  12. If the problem is in GUI tool, send me a screenshot
Not all items above are mandatory, but however if you provide quality feedback with much info describing your problem, I may help you with greater probability.
But please don't forget - mbldr is my hobby, there is no guarantee this software will work properly. I'm not responsible for any damage it may cause. Immediate support is also not guaranteed.


Here are some screenshots of mbldr version 1.43:

Mbldr boot menu is shown when PC is powered on or rebooted. Please note that it could easily be customized or hidden:
(It appears on the screen immediately after Power-On-Self-Test (PoST) is passed):

Mbldr boot menu itself
Boot menu itself

CLI version of mbldr installation/configuration program running under FreeDOS:

Main menu Adding a partition
Main configuration menu Adding a partition

CLI version of mbldr installation/configuration program running under Windows 98:

Configuring timed boot
Configuring timed boot

GUI version of installation/configuration program under Windows2000/Vista, FreeBSD and Linux:

Under Windows 2000 Under Windows Vista Under FreeBSD with GTK Under Linux with X11
Choosing device under Windows 2000 Choosing device under Windows Vista Choosing device under FreeBSD with GTK Choosing device under Linux with X11
Main configuration window under Windows 2000 Main configuration window under Windows Vista Main configuration window under FreeBSD with GTK Main configuration window under Linux with X11

Of course mbldrgui also works fine under Windows XP and looks similar to Windows 2000 and Vista. Also please note that under Linux/BSD it is recommended to use wxGTK engine of wxWidgets since X11/Universal works quite kludgy (at least for wxWidgets 2.8.3).



Since version 1.37 mbldr requires DPMI server in order to be run under MS-DOS or FreeDOS. You may use free CWS DPMI server (redistributable under the GPL). Release 5 of CWS DPMI could be found at ftp.delorie.com or here is a local copy.
GUI version of mbldr may require mingwm10.dll file. You may find it either in MinGW distribution or locally.

Version number Date Status Release short description
[Win98/ME, DOS],
December 12, 2008 Testing (may be unstable) Chainload feature, fix of hanging with timer interrupt, Czech translation, "restore from backup" changes.
[Win98/ME, DOS],
May 30, 2008 Issues reported Boot-timer fix on buggy BIOSes, French translation, hide/not hide other primary partitions, better description for drives under Windows, extra warning if no active partitions, few bug-fixes.
[Win98/ME, DOS],
November 23, 2007 Stable Initial version which supports interface localization using gettext (Russian is the only available translation for now except English) for DOS, Windows and *nix. Both GUI and CLI versions are affected.
[Win98/ME, DOS],
June 6, 2007 Stable New GUI configuration program (mbldrgui) which is based on wxWidgets library. Command-line mbldr renamed to mbldrcli (except DOS-version). Support for disks autodetection under Linux and FreeBSD.
[Win98/ME, DOS],
January 11, 2007 Stable Windows version of mbldr installation program is now able to detect hard disk size, bus type, vendor and model. DOS and Linux/BSD versions are not affected by this change.
[Win98/ME, DOS],
November 29, 2006 Stable The support of Microsoft Windows Vista has been introduced.
[Win98/ME, DOS],
November 15, 2006 Stable Now mbldr is fully covered with BSD license, all code written by Thomas is wiped out. Customizable progress-bar showing delay before timed boot that could also be used to indicate whether the timer is running/stopped. Maximum timeout was increased from 30 minutes to 10 hours. Some fixes and maitenance work described in changelog.
[Win98/ME, DOS],
October 31, 2006 Stable Installation/configuration program has been ported under Microsoft Windows, Boot loader is now able to remember the last booted OS as a default one for next boot, Configurable keys used to choose an operating system to boot (either '1', '2', etc. or 'F1', 'F2', etc.) (suggested by XM)
[Win98/ME, DOS],
August 18, 2006 Stable, obsolete Ported under Linux and FreeBSD while compatibility with MS-DOS/FreeDOS has been kept.
1.37 June 13, 2006 Stable, obsolete Boots OSes from logical disks on extended partition, TASM to NASM migration, Boot menu now supports up to 9 items, 'Skip boot' and 'Next HDD' menu items, much more free space for boot menu text, Installer was rewritten on C using DJGPP and RHIDE under FreeDOS, May configure any HDD, UPX compression of a binary
1.36 March 10, 2006 Stable, obsolete First release of mbldr, after more than 13 years. Includes 1024 cylinder fix and partition hiding.
1.35 December, 1992 Stable, obsolete It is actually OS-BS, stored here just as a starting point

Original release (1.35) of OS-BS project has been branched to create first official version (1.36) of mbldr (please note, that versions of mbldr below 1.36 do not exist).
The changelog for each version is available inside each package. However, the latest changelog is available here. For complete set of files available for download, look here.


There are some plans for the future. Feel free to suggest new features, send patches and improvements:
  1. Automatic detection of difference between partition tables in main MBR and chainloaded copy of MBR. Need to suggest user to keep them in sync every time the difference is found (at configuration time, not at boot time).

Help needed

  1. Starting from version 1.44 mbldr became localizeble. This means that user interface of graphic and text-based console configuration programs can be translated to other languages. Since I am Russian native speaker, it is very difficult for me to support anything except Russian and English. So I posted new open position to "Help wanted" section on the sf.net web-site which asks for new translations. But of course updates to existing translations are always welcome.
    Here are basic guidelines and hints for making and updating translations:
  2. It is needed to perform intensive testing on different hardware and software platforms and configurations
  3. Mbldr needs help in attempts to be compiled on different "non-standard" software configurations and operating systems
  4. Help in testing how HDD model/vendor detection mechanism works is also needed under different operating systems (especially different flavor or *nixes), with different controllers and hard disks Also you can take a look on ToDo section if you want to help with something else.

Translation status

Please note that even if translation is in "Complete" status it may require minor update as new strings appear in new versions of mbldr.

Language Status Authors Appears in Last updated in
English Complete Arnold Shade mbldr 1.44 mbldr 1.46
Russian Complete Arnold Shade mbldr 1.44 mbldr 1.46
French Partial Michelle Baert mbldr 1.45 mbldr 1.45
Czech Complete Ondrej Muller mbldr 1.46 SVN
Spanish Partial Rafael Garcia SVN SVN
Portuguese (Brazil) Complete Augusto Bodanese SVN SVN
Bengali Partial Farzana Khalid SVN SVN
Dutch Partial Chris van den Kieboom SVN SVN
Polish Complete Maciej Mrug SVN SVN

Building instructions

This section describes how to compile, link and package mbldr tools under different software platforms. Although it is really needed only for Linux/BSD, it could also be helpful under DOS and Windows if you decide to debug or improve mbldr:

Building under Linux and BSD-flavours

This step is mandatory since I don't distribute binary packages for Linux and BSD.
  1. Download the latest mbldr.tar.bz2 package to your local machine
  2. Untar and decompress it with "tar jxf mbldr.tar.bz2" command
  3. Minimal requirements for the building tools are: gcc, ld, nasm and xxd (is a part of vim package). You may also need strip, upx, ndisasm, tar and install. To build GUI version you will need installed development version of wxWidgets (including headers and libraries), g++ and wxrc (is a part of wxWidgets utilities).
  4. Invoke "./make_unix.sh" shell script or simply type "make". Please note that under BSD you need to use "gmake" instead of "make", so "./make_unix.sh" most probably will not work. Also please note that if you don't want to build GUI version of mbldr configuration program (or if you simply don't have wxWidgets) type "make mbldrcli" (similarly you may build only GUI version with "make mbldrgui").
  5. Be sure there is no compilation-time and linking-time errors on the screen
  6. To prepare Linux/BSD source-distribution package (similar to what you have downloaded) type "make dist" (you don't need this step, it is only for maintainers)
  7. To clean temporary object files and binary executable files type "make clean" (please note that "make distclean" is not implemented)
  8. To install/uninstall binary and documentation you may use "make install" or "make uninstall" respectively. The target directories are defined by DESTDIR and PREFIX environment variables so it is usually /usr.
  9. To begin using mbldr configuration program type "./mbldrcli" or "./mbldrgui". Append "-h" command-line switch to get on-line help.
That's it, I believe not too complex. I would be very appreciated if somebody undertakes the work of bringing mbldr to some modern Linux-distribution. Creating and keeping RPMs, ebuilds, Debian packages etc. up-to-date is really annoying for me.

Building under DOS and old Windows

This step is optional, mbldr archive for DOS contains precompiled binaries.
  1. DOS-version of mbldr supports command-line interface only (the binary is called mbldr.exe). Same binary should be used under Windows 98 and Windows ME
  2. Use MS-DOS or FreeDOS. I use "0.84 pre" version of FreeDOS, any newer version can also be used.
  3. Make sure cwsdpmi.exe is located in the directory listed in PATH environment variable (for example c:\tools\)
  4. Unzip all DJGPP archives (binary packages of bnu2161b, djdev203, gcc410b, gtxt040b, licv111b, mak3791b, rhid15ab, txi48b, fil41b) to c:\djgpp\ folder (uze unzip32.exe binary shipped with DJGPP to uncompress). You can use ZIP-picker for this and browse FTP folders on DJGPP web-site
  5. Make sure c:\djgpp\bin and c:\tools are in your PATH environment variable
  6. Add DJGPP environment variable to autoexec.bat and reboot ("set DJGPP=C:\DJGPP\DJGPP.ENV")
  7. Unzip upx.exe, xxd.exe (from VIM package for DOS), nasm.exe, ndisasm.exe, zip.exe (from InfoZIP package for DOS) from appropriate DOS packages to c:\tools\
  8. Go to the folder where you have unpacked sources of mbldr
  9. Type make_dos.bat

Building under NT-family of Windows

This step is optional, mbldr archive for Windows contains precompiled binaries.
  1. Similarly to Linux/BSD you may build either mbldrcli or mbldrgui or both. The requirements for GUI version are little bit more complex
  2. Download the latest mbldr.zip package to your local machine (please note that you need Windows zip-package. If you have downloaded zip archive for DOS, you will not be able to build Windows version)
  3. Unzip the package with the help of free InfoZIP or 7-ZIP archivers (under Windows XP you may use built-in ZIP decompressor - right-click on archive and choose "Extract all" item from context-menu)
  4. Install a recent GCC (gcc-core), binutils and mingw-runtime from MinGW web-site (you need to download binary packages from current/release branch and then unpack it to c:\mingw\ directory with the help of 7-ZIP archiver). Please note that if you are using Microsoft Internet Explorer it tends to rename .tar.gz archives to strange .tar.tar combination, so you need to rename them manually.
  5. Add c:\mingw\bin\ path to the %PATH% environment variable (this could be done using System applet in Control Panel, where you need to choose Advanced tab and then Environment Variables)
  6. Install GNU make package from MinGW web-site (it is distributed as executable, so there is no need to unpack it manually) Again, the target directory should be c:\mingw
  7. Install nasm into the same directory by unpacking zip archive (choose Win32 binaries in the download page). Check that nasm binaries appear in c:\mingw\bin directory.
  8. Install vim, the easiest way to do it is to install gvim package which is distributed as a Windows executable. Mbldr requires only xxd utility, so you need to copy xxd.exe from c:\Program Files\Vim\VimXX\ to c:\mibgw\bin\ directory (where XX is a version ov vim/gvim).
  9. Download Windows 32 API package from MinGW web-site and extract it in the same way.
  10. Download Libiconv and Gettext (can be found in section of MSYS Supplementary Tools) bin and dll packages from MinGW web-site and unpack them all to c:\mingw directory (please note that contents of /usr/local/ folders in archives should appear directly in c:\mingw\ for all 4 packages).
  11. You may also want to compress the result mbldr binary with UPX compressor (this is optional). Download the Win32 console version of compressor and unzip in into c:\mingw\bin\ (in fact you need only upx.exe file).
  12. Invoke a command-line interpreter (click on "Start" button, then "Run...", then type "cmd" in the edit-field) and switch to the directory where unpacked files of mbldr have been stored (this can be done with "cd" command)
  13. Type "make_win.bat mbldrcli.exe" to build command-line version of mbldr. If you don't need GUI version this is a last step. Store mbldrcli.exe somewhere and remove all intermediate directories (c:\mingw\, etc.). Roll-back changes in your %PATH% environment variable
  14. If you want to build GUI version of mbldr you need to download and compile wxWidgets library. There are several ways to perform wxWidgets compilation, I recommend to use MSYS and MinGW as described in wxWiki. wxWidgets is written in C++, so you need to download and extract G++ (gcc-g++) compiler from MinGW web-site.
  15. It is also needed to simulate Unix environment. It could be done with MSYS - install it from MinGW web-site (you need the main MSYS package, not the developer's toolkit). Use default target directory for installation (c:\msys\1.0\). In the console window that appears after MSYS installation process you need to agree to perform port-installation configuration steps. Then point it to c:/mingw/ directory (not c:/mingw/bin/). Note the type of slashes - these are forward in Unix-style.
  16. Update your %PATH% environment variable with c:\msys\1.0\bin\. Please note that MSYS path should be after MinGW path.
  17. Download wxMSW package in the form of executable from the wxWidgets web-site (Microsoft Windows port of wxWidgets library). Install it into default directory.
  18. Define new environment variable %WXWIN%. It should point to a directory where wxWidgets is installed (for example "c:\wxWidgets-2.8.4"). This should be done in the same way as for %PATH% environment variable. Please note that command-line interpreper should be reopened to use newly added environment variables.
  19. Run MSYS shell in a console window (using the desktop icon) and switch to wxWidgets directory using command like "cd c:wxWidgets-2.8.4/". Please note that there is no slash or backslash after disk specification ("c:").
  20. Use "./configure --enable-monolithic" script to adjust Makefiles. You may pass some parameters in order to enable or disable debugging, reduce the size of result binary by switching off some components, etc. For wxWidgets 2.8.4 I use "./configure --enable-monolithic --disable-shared --enable-optimise --disable-debug --disable-mem_tracing --disable-profile --enable-no_rtti --disable-no_exceptions --disable-compat24 --disable-compat26 --enable-image --enable-gif --disable-pcx --disable-tga --disable-iff --disable-pnm --disable-xpm --disable-icocur --without-libpng --without-libjpeg --without-libtiff --without-libxpm --without-libmspack --without-opengl --without-regex --without-zlib --without-odbc"
  21. If the previous step was completed successfully, use "make" to build the wxWidgets library.
  22. There is no need to invoke "make install", instead check (and update if necessary) values of CXXFLAGS and LIBRARIES variables in Makefile.win file (which is a part of mbldr distribution package). You may do it with vim or gvim that you have recently installed.
  23. If you want to create a Windows package of mbldr (in zip-archive) you need to install InfoZIP. Download ZIP (not UnZIP) utility and unpack zip.exe binary into c:\mingw\bin\ folder.
  24. Run command-line interpreper, switch to directory with mbldr sources and type "make_win.bat mbldrgui.exe" to build GUI version of mbldr configuration utility. You may also invoke "make_win.bat" without parameters to build both mbldrcli and mbldrgui.
  25. Copy mbldrgui.exe file to some place, uninstall unused software and wipe intermediate directories out. Also don't forget to restore your %PATH% and delete %WXWIN% environment variables.
There is no need to use Cygwin to compile mbldr under Windows, however you may try, it could work in theory. Also I have not checked whether mbldr could be built using Microsoft Visual C++. Feel free to try and report the results.


I would appreciate any feedback from users of mbldr. I am mostly interested in bugs (crashes, hangings, etc.), but of course I am also interested in success stories. The recommended way to contact current maintainer is to use an appropriate mechanism on sourceforge project site (forum, tracker, bugs, feature requests, etc.). There is no hypertext references in the e-mail addresses below due to spam bots protection:

Current maintainer of mbldr is Arnold Shade (what is a nickname due to several reasons being anonymous). Use it to refer mbldr 1.36 and above.

The author of OS-BS is Thomas Wolfram. Use it to refer os-bs 1.35 and below (which is also called mbldr 1.35):

Note: you need to replace " __dot__ " with "." and " __at__ " with "@" before using the addresses above.


Project related resources:

Pages related to OS-BS project:

Similar projects (other boot managers):

Assembly language descriptions and CPU instructions set Partition tables and boot loaders Development and packaging stuff Operating-systems related BIOS and ATA specifications

Last updated: December 12, 2008

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