Put David's and my answer regarding loader and kernel memory usage

here.

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+~From: J Wunsch <j@uriah.heep.sax.de>
+~Message-Id: <199504160843.KAA16160@uriah.heep.sax.de>
+~Subject: Memory usage (Was Re: Memory init pattern)
+~To: freebsd-hackers@FreeBSD.org (FreeBSD hackers)
+~Date: Sun, 16 Apr 1995 10:43:29 +0200 (MET DST)
+
+[Audience extended to -hackers, since it's a general topic.]
+
+As Frank Durda IV wrote:
+> 
+> By the way, I have seen no description of how FreeBSD uses PC memory, ie
+> what 0-640K gets used for, does the kernel load there or higher,
+> is the kernel relocated, etc.  Is there a paper on this?
+
+Since i've just digged through the boot code, i can tell you what's
+going there. :)  [Someone going to collect this sort of messages
+and making a kernel hackers manual?]
+
+The boot sector will be loaded at 0:0x7c00, and relocates itself
+immediately to 0x7c0:0.  (This is nothing magic, just an adjustment
+for the %cs selector, done by an ljmp.)
+
+It then loads the first 15 sectors at 0x10000 (segment BOOTSEG in the
+biosboot Makefile), and sets up the stack to work below 0x1fff0.
+After this, it jumps to the entry of boot2 within that code.  I.e., it
+jumps over itself and the (dummy) partition table, and it's going to
+adjust the %cs selector -- we are still in 16-bit mode there.
+
+boot2 asks for the boot file, and examines the a.out header.  It masks
+the file entry point (usually 0xf0100000) by 0x00ffffff, and loads the
+file there.  Hence the usual load point is 1 MB (0x00100000).  During
+load, the boot code toggles back and forth between real and protected
+mode, to use the BIOS in real mode.
+
+The boot code itself uses segment selectors 0x18 and 0x20 for %cs and
+%ds/%es in protected mode, and 0x28 to jump back into real mode.  The
+kernel is finally started with %cs 0x08 and %ds/%es/%ss 0x10, which
+refer to dummy descriptors covering the whole address space.
+
+The kernel will be started at its load point.  Since it's been linked
+for another (high) address, it will have to execute PIC until the page
+table and page directory stuff is setup properly, at which point
+paging will be enabled and the kernel finally runs at the address
+where it has been linked to.
+
+[... -- no longer valid]
+
+The later memory usage (once paging is enabled) could better be
+explained by the VM folks.
+
+-- 
+cheers, J"org
+
+joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/
+Never trust an operating system you don't have sources for. ;-)
+
+~Message-Id: <199504160955.CAA00143@corbin.Root.COM>
+~To: freebsd-hackers@FreeBSD.org (FreeBSD hackers)
+~Subject: Re: Memory usage (Was Re: Memory init pattern) 
+~From: David Greenman <davidg@Root.COM>
+~Date: Sun, 16 Apr 1995 02:55:50 -0700
+
+...
+   The physical pages immediately following the kernel BSS contain proc0's page
+directory, page tables, and upages. Some time later when the VM system is
+initialized, the physical memory between 0x1000-0x9ffff and the physical memory
+after the kernel (text+data+bss+proc0 stuff+other misc) is made available in
+the form of general VM pages and added to the global free page list.
+   Does this answer the question?
+
+-DG
+