From owner-freebsd-current@FreeBSD.ORG  Tue Nov  9 17:11:10 2010
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Delivered-To: current@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id D62BE106566B;
	Tue,  9 Nov 2010 17:11:10 +0000 (UTC)
	(envelope-from bakul@bitblocks.com)
Received: from mail.bitblocks.com (bitblocks.com [64.142.15.60])
	by mx1.freebsd.org (Postfix) with ESMTP id BB0158FC14;
	Tue,  9 Nov 2010 17:11:10 +0000 (UTC)
Received: from bitblocks.com (localhost.bitblocks.com [127.0.0.1])
	by mail.bitblocks.com (Postfix) with ESMTP id 942D95B89;
	Tue,  9 Nov 2010 09:04:53 -0800 (PST)
To: Julian Elischer <julian@freebsd.org>
In-reply-to: Your message of "Tue, 09 Nov 2010 08:45:14 PST."
	<4CD97A9A.8000007@freebsd.org> 
References: <4CD97A9A.8000007@freebsd.org>
Comments: In-reply-to Julian Elischer <julian@freebsd.org>
	message dated "Tue, 09 Nov 2010 08:45:14 -0800."
Date: Tue, 09 Nov 2010 09:04:53 -0800
From: Bakul Shah <bakul@bitblocks.com>
Message-Id: <20101109170453.942D95B89@mail.bitblocks.com>
Cc: alc@freebsd.org, FreeBSD Current <current@freebsd.org>
Subject: Re: limits to memory on amd64 
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
	<freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>, 
	<mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 09 Nov 2010 17:11:10 -0000

On Tue, 09 Nov 2010 08:45:14 PST Julian Elischer <julian@freebsd.org>  wrote:
> During the discussion at MeetBSD the question came up as to what the real
> limiting factors were with regard to how much RAM a system could have.
> it was put to us that the limit was currently around 512 GB, though no-one
> at teh discussion knew what the mechanism of the limitation was or 
> what might ligh beyond it.
> 
> Could anyone who knows, pipe upt and let use know what the factors are,
> and if the current limit is overcome, what the next one after that will be?

You mean beyond architectural limits?

>From Wikipedia:

    Larger physical address space: The original
    implementation of the AMD64 architecture implemented
    40-bit physical addresses and so could address up to 1 TB
    (2^40 bytes) of RAM. Current implementations of the AMD64
    architecture (starting from AMD 10h microarchitecture)
    extend this to 48-bit physical addresses and therefore
    can address up to 256 TB of RAM. The architecture permits
    extending this to 52 bits in the future (limited by the
    page table entry format); this would allow addressing of
    up to 4 PB of RAM.