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Mike Gonta



Joined: 26 Dec 2010
Posts: 238
Location: the-ideom
Mike Gonta
Everything else you always wanted to know about USB booting but were too USB (Unable or Sophisticated or Busy) to ask.

USB Booting Secret # 3: If the PC can boot from USB, you can use the BIOS to access the entire flash drive.
Interrupt 13h, ah=42h Extended Read and ah=43h Extended Write can be used for USB flash drive LBA access.

The BIOS Enhanced Disk Drive Specification (Version 3.0 March 12, 1998) is supported on all current PC's. This was written by
Phoenix (one of the big "3" BIOS makers) with contributions from Intel, Microsoft and others. It provides LBA support for
removable drives (the USB flash drive was first released commercially in 2000).
The concept of FDD and HDD emulation used for int 13h CHS functions does not apply.

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Last edited by Mike Gonta on 08 Feb 2012, 23:44; edited 2 times in total
Post 30 Jan 2011, 20:41
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Dex4u



Joined: 08 Feb 2005
Posts: 1601
Location: web
Dex4u
Dos can readwrite to usb flash drive fat12, fat16 ,fat32, if you boot from it.

Also 32bit DexOS can readwrite to a usb flash drive fat12, fat16 ,fat32.
for the past 5 years.
Thats why it as both bios and pm drivers.
Post 31 Jan 2011, 14:39
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Mike Gonta



Joined: 26 Dec 2010
Posts: 238
Location: the-ideom
Mike Gonta
Dex4u wrote:
Dos can readwrite to usb flash drive fat12, fat16 ,fat32, if you boot from it.
Also 32bit DexOS can readwrite to a usb flash drive fat12, fat16 ,fat32. for the past 5 years.
DexUsbBoot - ReadMe.txt wrote:
In this zip you will find one format program to format the usb FAT (fat16), and a program to put the
DexOS + app on a usb drive, so as to boot from it as Fdd or Hdd emulation.

Funny paraphrase wrote:
You can boot the same USB flash drive on some PC's some of the time, but you can't boot the same
USB flash drive on all PC's all of the time

Not true
The USB flash drive is a single device capable of booting and running the complete capacity on all machines that can
boot USB irregardless of BIOS emulation. Two different drives with 2 different file systems are not required for
universal booting.

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Mike Gonta
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Post 31 Jan 2011, 23:52
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Dex4u



Joined: 08 Feb 2005
Posts: 1601
Location: web
Dex4u
Mike Gonta wrote:

Not true
The USB flash drive is a single device capable of booting and running the complete capacity on all machines that can
boot USB irregardless of BIOS emulation. Two different drives with 2 different file systems are not required for
universal booting.


I think you have done your testing on a limited number of PC's.
See here: http://f.osdev.org/viewtopic.php?f=1&t=19681
Note: its got 2 pages

Quote:
Mike Gonta
look and see - many look but few see

Maybe you should take your own advice Wink
Post 01 Feb 2011, 00:29
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Madis731



Joined: 25 Sep 2003
Posts: 2140
Location: Estonia
Madis731
I'm gonna take Mike's side here. It is true that it would seem to be impossible to boot some PCs/laptops, but actually you just need to know how to present it to the BIOS. I've had troubles booting HP-laptops, but they finally surrendered. Its because USB has a bit more structure than a simple floppy. When you rawwrite a 1.38MB image to a floppy you can be 100% sure that it contains what you mean it to contain.
I made the mistake assuming USB will act the same way, but I needed to write to the absolute 0-address for it to work on a HP laptop because they tend to read that 0 address and don't even look further to emulate a floppy.

The fact is that you can make your USB stick act the way you want, HDD/FDD/ODD... and even partition it.
Post 01 Feb 2011, 19:11
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Mike Gonta



Joined: 26 Dec 2010
Posts: 238
Location: the-ideom
Mike Gonta
Hi Madis731,
Madis731 wrote:
I'm gonna take Mike's side here.

We're all on the same side here (including Craig). We are FASM board members, not flame throwers from osdev.

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Mike Gonta
the-ideom - now you know how to compile

https://mikegonta.com
Post 01 Feb 2011, 21:39
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Coty



Joined: 17 May 2010
Posts: 554
Location: ␀
Coty
@Mike Gonta: I agree with Dex. I have a desktop PC here that will NOT boot from FDD emulation. (It shows my USB as an HDD and only boots from it with HDD emulation). Yes, have tried... Thus I believe that two methods are required for universal booting. However my other 5 USB bootible computers with boot from any method FDD or HDD.

Mike Gonta wrote:
We're all on the same side here (including Craig). We are FASM board members, not flame throwers from osdev.

I am sorry but... Ironic quote is ironic! (I don't mean to offend with that!)

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Post 01 Feb 2011, 21:50
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