From owner-freebsd-hackers@FreeBSD.ORG  Wed Sep 29 19:33:05 2004
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From: "vijay singh" <vijju_s@hotmail.com>
To: freebsd-hackers@freebsd.org
Date: Wed, 29 Sep 2004 12:32:53 -0700
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Subject: about freebsd boot1.S
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hello all, i am trying to understand the freebsd boot code. i saw that the 
1st stage boot loader relocates itself from 7c00 to 700. why is this done? 
if the run time kernel were to switch to real-mode and transfer control to 
this location (0700) would the 1st stage boot program run again?

for the output below, i used the BIOS debugger and read the 1st sector into 
7c00, and unassebled the text.

0000:00007C1D   cld
0000:00007C1E   xor     cx, cx	/* cx = 0 */
0000:00007C20   mov     es, cx	/* es = 0 */
0000:00007C22   mov     ds, cx	/* ds = 0 */
0000:00007C24   mov     ss, cx	/* ss = 0 */
0000:00007C26   mov     sp, 7C00	/* set SP to current location */
0000:00007C29   mov     si, sp
0000:00007C2B   mov     di, 0700	/* DS:SI pair denotes the source string and 
ES:DI pair the destination string 0:7C00 -> 0:700 */
0000:00007C2E   inc     ch	/* ch = 1, cx = 100*/
0000:00007C30   repe		/* repeat the movsw instruction cx number of times */
0000:00007C31   movsw	/* moves 200h = 512 bytes from 7C00 to 700*/

please cc me in your reply.
thanks
vijay