Re: BootProg released

From	"James Harris" <james.harris.1@gmail.com>
Newsgroups	alt.os.development
Subject	Re: BootProg released
Date	2015-07-06 21:42 +0100
Organization	A noiseless patient Spider
Message-ID	<mnep4l$ioc$1@dont-email.me> (permalink)
References	(2 earlier) <ca5622b0-3742-49d5-a136-a6af5b808d9c@googlegroups.com> <mn0don$1ac$1@dont-email.me> <op.x1bbg12dmsr2db@dell3100.workgroup> <mnc4sr$jam$1@dont-email.me> <op.x1ci1fsamsr2db@dell3100.workgroup>

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"Kerr Mudd-John" <admin@127.0.0.1> wrote in message 
news:op.x1ci1fsamsr2db@dell3100.workgroup...
> On Sun, 05 Jul 2015 21:44:31 +0100, James Harris 
> <james.harris.1@gmail.com> wrote:
>> "Kerr Mudd-John" <admin@127.0.0.1> wrote in message 
>> news:op.x1bbg12dmsr2db@dell3100.workgroup...
>>> On Wed, 01 Jul 2015 11:02:17 +0100, James Harris 
>>> <james.harris.1@gmail.com> wrote:

...

>>>> * Move code so that the loaded file can start at 0x7c00.

...

>> I found the following. It explains in some detail why 0x7c00 was 
>> chosen.  I don't know whether it is correct or not but it sounds 
>> valid and makes  an interesting read: basically that the lowest 
>> practical amount of RAM  that the original IBM PC could run IBM DOS 
>> 1.0 on was 32k so they chose  the 31k point (i.e. 0x7c00).
>>
>>   http://www.glamenv-septzen.net/en/view/6

...

> OK. But we don't need to be so constrained nowadays

7c00 is a bit of a de-facto standard. Apart from the BIOS loading floppy 
and hard disk boot sectors there it is used in other contexts too. The 
Microsoft MBR copies itself to 0x600 and loads a VBR to 0x7c00. And PXE 
bootroms I have used load their targets to 0x7c00. And some loaded boot 
code *expects* to have been loaded to that address.

But having read over the linked page above ISTM better to ignore it 
unless need dictates otherwise.

My FAT boot sector currently loads its target to 0x1_0000, i.e. 64k and 
it loads up to the first 64k of that file.

I may one day change the FAT boot sector to load to 0x8000, i.e. 32k. 
Not sure.

James

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Thread

BootProg released "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-06-21 22:52 -0700
  Re: BootProg released "James Harris" <james.harris.1@gmail.com> - 2015-06-22 14:12 +0100
    The BIOS Drive ID urban legend "Mike Gonta" <mikegonta@gmail.com> - 2015-06-24 17:49 -0400
      Re: The BIOS Drive ID urban legend (was: BootProg released) "James Harris" <james.harris.1@gmail.com> - 2015-07-01 10:44 +0100
    Re: BootProg released "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-06-25 21:08 -0700
      Re: BootProg released "James Harris" <james.harris.1@gmail.com> - 2015-07-01 11:02 +0100
        Re: BootProg released "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-07-04 05:18 -0700
        Re: BootProg released "Kerr Mudd-John" <admin@127.0.0.1> - 2015-07-05 19:11 +0100
          Re: BootProg released "Kerr Mudd-John" <admin@127.0.0.1> - 2015-07-06 10:52 +0100
            Re: BootProg released "James Harris" <james.harris.1@gmail.com> - 2015-07-06 21:42 +0100

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