From owner-freebsd-questions@FreeBSD.ORG Tue Jul 1 17:06:48 2003 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id D416F37B401 for ; Tue, 1 Jul 2003 17:06:48 -0700 (PDT) Received: from falcon.midgard.homeip.net (h76n3fls20o913.bredband.comhem.se [213.67.148.76]) by mx1.FreeBSD.org (Postfix) with SMTP id E597344057 for ; Tue, 1 Jul 2003 17:06:46 -0700 (PDT) (envelope-from ertr1013@student.uu.se) Received: (qmail 5049 invoked by uid 1001); 2 Jul 2003 00:06:42 -0000 Date: Wed, 2 Jul 2003 02:06:42 +0200 From: Erik Trulsson To: Joshua Oreman Message-ID: <20030702000642.GA5018@falcon.midgard.homeip.net> Mail-Followup-To: Joshua Oreman , george donnelly , questions@freebsd.org References: <20030701234655.GA72522@webserver.get-linux.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20030701234655.GA72522@webserver.get-linux.org> User-Agent: Mutt/1.5.4i cc: questions@freebsd.org Subject: Re: 4GB RAM limit? X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 02 Jul 2003 00:06:49 -0000 On Tue, Jul 01, 2003 at 04:46:55PM -0700, Joshua Oreman wrote: > On Tue, Jul 01, 2003 at 06:30:13PM +0000 or thereabouts, george donnelly wrote: > > hi > > > > I've got a 4.7 freebsd machine and after upgrading from 4 to 6GB of RAM, top > > does not recogmize the other 2 GB (only shows 4) and actually there was a > > message that said "ignoring 2 GB". > > > > Can anyone shed light on this or suggest where i can look to understand > > this? > > AFAIK, on i386 the maximum addressable memory space is 4096 MB. > Here's why: > C pointer = 4 bytes = maximum value 4294967296 Yes and no. i386 addresses are indeed 32 bits which means that a process can only address 4GB worth of memory. On the Pentium Pro and later x86 CPUs there some special tricks that can be used to have a physical address space of 36 bits (64 GB memory), even though a single process still only can use 4 GB. FreeBSD 4.x and earlier does not have any support for those tricks so it cannot use more than 4 GB of RAM. FreeBSD 5.1 and later does have support for PAE (Physical Address Extension) so it can handle up to 64 GB RAM (while a single process is still constrained to a 32-bit address space.) -- Erik Trulsson ertr1013@student.uu.se