From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lists.gentoo.org (pigeon.gentoo.org [208.92.234.80]) by finch.gentoo.org (Postfix) with ESMTP id 050021381F3 for ; Wed, 9 Oct 2013 02:17:36 +0000 (UTC) Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id A10E8E0932; Wed, 9 Oct 2013 02:17:28 +0000 (UTC) Received: from smtp.cs.nyu.edu (SMTP.CS.NYU.EDU [128.122.49.97]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by pigeon.gentoo.org (Postfix) with ESMTPS id 9D4E0E0908 for ; Wed, 9 Oct 2013 02:17:27 +0000 (UTC) Received: from newlap.localdomain (ool-182df6e9.dyn.optonline.net [24.45.246.233]) (authenticated bits=0) by smtp.cs.nyu.edu (8.14.3/8.14.4) with ESMTP id r992HLLd017766 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT) for ; Tue, 8 Oct 2013 22:17:24 -0400 (EDT) Received: by newlap.localdomain (Postfix, from userid 1000) id 52888A00E5; Tue, 8 Oct 2013 22:17:21 -0400 (EDT) From: gottlieb@nyu.edu To: gentoo-user@lists.gentoo.org Subject: Re: [gentoo-user] re: NX (Execute Disable) protection cannot be enabled: non-PAE kernel! [dmesg] References: <52530B6D.5080707@gmail.com> <52530E8C.1040701@gmail.com> <52543B10.10201@gmail.com> <52547725.3030209@gmail.com> Date: Tue, 08 Oct 2013 22:17:21 -0400 In-Reply-To: <52547725.3030209@gmail.com> (Alan McKinnon's message of "Tue, 08 Oct 2013 23:20:37 +0200") Message-ID: <87eh7vgpce.fsf@nyu.edu> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@lists.gentoo.org Reply-to: gentoo-user@lists.gentoo.org MIME-Version: 1.0 Content-Type: text/plain X-Archives-Salt: ece4504c-c171-4244-8e99-f0b99dcf6eaa X-Archives-Hash: 5373d5c721c8ef362197ea05dfd06019 On Tue, Oct 08 2013, Alan McKinnon wrote: > That is correct, with 3G physica RAM, you will not benefit from using > PAE at all. I don't think it interferes with anything if you do have it, > I recall a time when RedHat shipped 32 bit kernels that were PAE-enabled. > > Briefly, the way it works is that the kernel assigns blocks of memory to > different processes. So a single process can still only access 4G of > memory, but two different process don't anymore have to address the same > 4G of memory like you must do without PAE. But you still don't get to > give your 32 bit database more than 4g of RAM Agreed. Virtual addresses refer to those in the program (really process). Physical addresses address refer to those in the hardware (i.e. addresses in the RAM itself). To have a single process able to access extra memory would be to increase the *virtual* address range. PAE (*physical* address extension) enables more RAM to be accessed (by the hardware not by a single process), but does not increase the virtual address range. When pdp-11s added I and D space, that increased the virtual address range by a factor of two. The I/D bit (instruction/data) was essentially an extra bit of virtual address. allan