Acronis MBR
Hi,
I'm intending to make a tool for creating bootable USB. I have concerns about MBR of Acronis Loader, I was looking at the first 512byte and I do not understand the byte at 0x1B5, what is it and how to calculate it?
Please help me, thank all!

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Hi, thank you!
I see its value changes based on the StartingOffset of partition. I've used multiple partitions on USB and it shows the value is always different for each. It is not fixed even though the language is not changed.
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Don't get hung up on 512 offset shown in diskpart - that's not an accurate reflection of the parition offset value. You need to calculate the offset with the following method. After restoring with Acronis, it has been an even value in all instances I have checked on.
https://www.techpowerup.com/articles/other/157
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I do not understand what you are talking about, I use Bootable Media Builder in Acronis Disk Director to create USB bootable
Its value changes based on the Offset but it is not the value of the Offset.
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I don't think you're going to get an answer from the user community for your initial question. My response was to help identify that the offset will be different in many cases, but still ends up being an equal value when calculated correctly. There have been a few other questions like yours where most people were concerned because the offset was not actually 512 after recovering from an image with Acronis - that is the purpose of the calculator I provided, so that one can verify that the paritions are actually aligned, despite the value not being 512, and in some cases, not even an even number.
As for the value of that sector on your thumb drive - no idea.
What is your convern of the bootable rescue media and how would that impact your tool to create bootable media? Why build your own? You can build bootable media for WinPE using DISM commands. There are a ton of tools that can do this for you already as well - Rufus, iso 2 usb, rmprep, etc. If you know your payload, you can also use other media creation tools (like Acronis or DISM, or whatever) and simply change the payload after the media is created. Additionally, there are multiboot tools (although most are limited to legacy booting at this time - but still handy) such as Yumi and my personal favorite - Easy2Boot.
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Rob:
I think you missed Tu's point. He wasn't inquiring about partition offset issues; that's an entirely different topic. He was just curious about the function of three bytes in the first sector of an MBR disk. He noticed that Acronis boot media creates an MBR that differs slightly from the MBR created by Windows tools. The link in my reply #1 should answer most of his questions about the function of these three bytes; it even has the disassembled assembly language code that uses those bytes.
However, it doesn't answer the question of why Acronis chose to do things slightly differently. I don't know this answer either. I suspect that the reasons have something to do with the Acronis Startup Recovery Manager (ASRM) that can be activated in TI (press F11 key at boot time to boot to a standalone Acronis Linux loader). Activating the ASRM changes the standard error messages in the MBR as well as the boot loader code. You can see this from the attached two pictures.
The file "Standard Windows MBR" is a disk editor view (in Hex and ASCII) using Acronis Disk Director 12's disk editor to view the MBR on my VM's primary disk.
The file "ASRM Activated" file shows the same view of the same disk after activating the Acronis Startup Recovery Manager. Note how different the error messages are (highlighted in blue in both files), not to mention the completely different executable boot code from 0x0000 through 0x0162. You can also see the three bytes Tu was talking about at 0x01b5 through 0x01b7; these are the bytes that he was inquiring about.
If Tu is a developer and wants to make a tool for creating bootable USB drives, why discourage him?
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Mark Wharton has said exactly what I want. Tools that I'm developing is AIO Boot.
https://www.sitecuatui.com/aio-boot-v0-9/
http://www.softpedia.com/get/System/Boot-Manager-Disk/AIO-Boot.shtml
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