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rufus/res/mbr/readme.txt

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[mbr] add LBA sector readout, as required by some BIOSes * I'm looking at you, Dell Optiplex! * also fix boot in case no secondary bootable drive exists * also adds a readme
2012-03-20 20:31:54 +00:00
Rufus: The Reliable USB Formatting Utility - Custom MBR
# Description
This directory contains all the resources required to create an MBR that prompts
the user for boot selection, when a second bootable device (typically bootable
[mbr] various fixes and improvements * Adds USB masquerading according to disk ID in USB part table * Adds debug feature * Closes #74 - was due to flags not being properly saved/restored * Closes #71 * Fixes reentrant INT_13h for some platforms (eg. IBM t43p reenters INT_13h to issue an SCSI passthrough, AH=0x50) * Embed MBR as a resource rather than an ms-sys header
2012-03-25 20:35:38 +00:00
fixed HDD) is reported by the BIOS at 0x81.
[mbr] add LBA sector readout, as required by some BIOSes * I'm looking at you, Dell Optiplex! * also fix boot in case no secondary bootable drive exists * also adds a readme
2012-03-20 20:31:54 +00:00
This aims at mimicking the Microsoft Windows optical installation media feature,
[ui] add advanced mode * Adds "bare" Syslinux, Rufus MBR and disabling of fake USB detection options
2012-05-16 22:38:39 +00:00
which may be necessary on for WinPE based installations.
[mbr] add LBA sector readout, as required by some BIOSes * I'm looking at you, Dell Optiplex! * also fix boot in case no secondary bootable drive exists * also adds a readme
2012-03-20 20:31:54 +00:00
[mbr] various fixes and improvements * Adds USB masquerading according to disk ID in USB part table * Adds debug feature * Closes #74 - was due to flags not being properly saved/restored * Closes #71 * Fixes reentrant INT_13h for some platforms (eg. IBM t43p reenters INT_13h to issue an SCSI passthrough, AH=0x50) * Embed MBR as a resource rather than an ms-sys header
2012-03-25 20:35:38 +00:00
This MBR will also masquerade a bootable USB drive booted as 0x80 by the BIOS to
a different ID according to the one found in its partition table entry. Eg. if
the partition table lists the disk ID for the first partition as 0x81, then it
will be swapped for 0x80.
[mbr] replace gpt.S with a more generic msg.S * msg.S now reads an ASCII message (with escaped colour sequences) from the following blocks, which is both more flexible and allows for more content to be displayed. * Also adds Bochs testing to the MBR build facility
2020-02-19 14:22:14 +00:00
An additional MBR (msg.S) also exists in this directory, that can be used to
[core] fix MBR protective message overwriting the primary GPT * We distractedly chose to populate the message from our protective MBR for GPT/UEFI-only boot media into the 4KB that directly followed the MBR, which of course is space that is being used by the primary GPT. * This resulted on systems having to fall back to using the secondary GPT, which not all appear to be designed to do. * Alter the code to ensure the protective message is written at LBA 34, after the primary GPT. * Closes #1507
2020-04-13 16:05:33 +00:00
display an ASCII message contained in the sectors following the primary GPT
(LBA sectors 34 and later).
[mbr] replace gpt.S with a more generic msg.S * msg.S now reads an ASCII message (with escaped colour sequences) from the following blocks, which is both more flexible and allows for more content to be displayed. * Also adds Bochs testing to the MBR build facility
2020-02-19 14:22:14 +00:00
This can be used, for instance, to display a notice for media that cannot be
booted in BIOS/Legacy mode.
[mbr] add LBA sector readout, as required by some BIOSes * I'm looking at you, Dell Optiplex! * also fix boot in case no secondary bootable drive exists * also adds a readme
2012-03-20 20:31:54 +00:00
# Compilation
Any gcc suite (except possibly the X-Code one on OS-X) should be able to compile
the MBR by invoking 'make'. A 'make dis', that produces a disassembly dump is
[mbr] replace gpt.S with a more generic msg.S * msg.S now reads an ASCII message (with escaped colour sequences) from the following blocks, which is both more flexible and allows for more content to be displayed. * Also adds Bochs testing to the MBR build facility
2020-02-19 14:22:14 +00:00
also provided for your convenience. If you have the Bochs emulator installed,
you can also invoke 'make test' to test the MBR with Bochs.
[mbr] add LBA sector readout, as required by some BIOSes * I'm looking at you, Dell Optiplex! * also fix boot in case no secondary bootable drive exists * also adds a readme
2012-03-20 20:31:54 +00:00
# Primer
The way this bootloader achieves the feature highlighted above is as follows:
1. An attempt to read the MBR of the second bootable drive (0x81) is made
through INT_13h (in either CHS or LBA mode depending on the extensions
detected)
2. If that attempts succeeds, then the partition table from the newly read MBR
is checked for an active/bootable entry.
3. If such a partition is found, a prompt is displayed to the user and an RTC
timer interrupt (INT_8h) override is added so that dots are displayed at
regular interval. Then the keyboard is checked for entry.
4. If the user presses a key, the first partition boot record from the USB is
read (according to the values found in the USB MBR partition table) and
executed
5. If no key is pressed, then an INT_13h (disk access interrupt) override is
added to masquerade the second bootable drive (0x81) as the first one (0x80)
so that the Windows second stage installer, or any other program relying on
BIOS disk access, behave as if there was no USB drive inserted.
6. In case there was a failure to read the second bootable drive's MBR, or no
active partition was detected there, the USB is booted without prompts.
[mbr] various fixes and improvements * Adds USB masquerading according to disk ID in USB part table * Adds debug feature * Closes #74 - was due to flags not being properly saved/restored * Closes #71 * Fixes reentrant INT_13h for some platforms (eg. IBM t43p reenters INT_13h to issue an SCSI passthrough, AH=0x50) * Embed MBR as a resource rather than an ms-sys header
2012-03-25 20:35:38 +00:00
7. In case USB is booted, and the drive ID of first partition of the USB (which
is always assumed bootable) is read and if different from 0x80, then it is
also swapped with 0x80 in the INT_13h override.
[mbr] add LBA sector readout, as required by some BIOSes * I'm looking at you, Dell Optiplex! * also fix boot in case no secondary bootable drive exists * also adds a readme
2012-03-20 20:31:54 +00:00
# Limitations
* If you are using software RAID or a non-conventional setup, the second
bootable disk may not be accessible through the BIOS and therefore the USB
[mbr] various fixes and improvements * Adds USB masquerading according to disk ID in USB part table * Adds debug feature * Closes #74 - was due to flags not being properly saved/restored * Closes #71 * Fixes reentrant INT_13h for some platforms (eg. IBM t43p reenters INT_13h to issue an SCSI passthrough, AH=0x50) * Embed MBR as a resource rather than an ms-sys header
2012-03-25 20:35:38 +00:00
will always be booted.
* Some processes (notably XP's ntdetect.com) do not seem to like gaps in the
bootable drive sequence, which means that if you set your bootable USB
partition as 0x82 or higher, and it leaves any of 0x80/0x81 free as a result
then these processes may report an error.
* DOS also does not allow anything but 0x80 to be used as bootable disk. Thus
it is not possible to run MS-DOS or FreeDOS off an USB drive unless the disk
ID is 0x80 and not masqueraded.
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