From owner-freebsd-questions@FreeBSD.ORG Wed Jul 9 12:36:59 2008 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 60C2E1065674 for ; Wed, 9 Jul 2008 12:36:59 +0000 (UTC) (envelope-from raghu@mri.ernet.in) Received: from hrimail.hri.res.in (hrimail.hri.res.in [210.212.50.7]) by mx1.freebsd.org (Postfix) with ESMTP id 2CB018FC20 for ; Wed, 9 Jul 2008 12:36:58 +0000 (UTC) (envelope-from raghu@mri.ernet.in) Received: from ipc2.mri.ernet.in (unknown [192.168.3.2]) by hrimail.hri.res.in (Postfix) with ESMTP id 05E2097EFB; Wed, 9 Jul 2008 18:13:40 +0530 (IST) Received: from ipc2 (localhost [127.0.0.1]) by ipc2 (Postfix) with SMTP id 4403E1D4A7; Wed, 9 Jul 2008 18:06:33 +0530 (IST) Received: from riemann.mri.ernet.in (riemann.mri.ernet.in [192.168.3.122]) by ipc2.mri.ernet.in (Postfix) with ESMTP id 19C1917FD5; Wed, 9 Jul 2008 18:06:33 +0530 (IST) Received: from riemann.mri.ernet.in (localhost [127.0.0.1]) by riemann.mri.ernet.in (8.13.6/8.13.6) with ESMTP id m69CU07x045595; Wed, 9 Jul 2008 18:00:00 +0530 (IST) (envelope-from raghu@riemann.mri.ernet.in) Received: (from raghu@localhost) by riemann.mri.ernet.in (8.13.6/8.13.6/Submit) id m69CTob1045594; Wed, 9 Jul 2008 17:59:50 +0530 (IST) (envelope-from raghu) From: "N. Raghavendra" To: Robert Heron In-Reply-To: <1FC03320-82E6-4ADD-AE3F-E0BAD48AF4D0@heron.pl> (Robert Heron's message of "Sat, 5 Jul 2008 13:04:19 +0200") References: <1FC03320-82E6-4ADD-AE3F-E0BAD48AF4D0@heron.pl> X-Organization: Harish-Chandra Research Institute (HRI) X-Address: Chhatnag Road, Jhusi, Allahabad 211 019, India X-URL: http://www.mri.ernet.in/ and http://www.retrotexts.net/ X-Phone: +91 (532) 2667 509, 2667 318, 2667 578, 2567 746, 2567 747 X-Fax: +91 (532) 2667 576, 2567 748, 2567 444, 2568 036 X-OpenPGP-Key-ID: 0x03618806 X-OpenPGP-Key-Fingerprint: C75D D0AF 457E 7454 BEC2 37AD C6E1 0407 0361 8806 X-OpenPGP-Public-Key-Available-At: http://www.keyserver.net/ Date: Wed, 09 Jul 2008 17:59:50 +0530 Message-ID: <86ej63z1dt.fsf@riemann.mri.ernet.in> User-Agent: Gnus/5.110004 (No Gnus v0.4) Emacs/22.0.50 (berkeley-unix) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: freebsd-questions@freebsd.org Subject: Re: FreeBSD 7.0 and RAM limit X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: "N. Raghavendra" List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 09 Jul 2008 12:36:59 -0000 At 2008-07-05T13:04:19+02:00, Robert Heron wrote: > FreeBSD 7.0-R on i386 server with motherboard S5000VSA and 6GB RAM > onboard. BIOS version - 88 (the latest) > > Kernel includes: options MAXMEM=(6*1024*1024) > > And FreeBSD reports only: > > real memory = 2680160256 (2556 MB) > avail memory = 2617892864 (2496 MB) > > Why? What is wrong that FreeBSD sees only about 2.5GB instead of > 6GB? (I ran into this question recently when buying a computer, and did some homework on it, however my understanding may be off the mark.) As mentioned in earlier replies, the problem isn't caused by the OS, but is a limitation of the i386 architecture, in which each byte of memory is indexed by a 32-bit integer. This means that an i386 machine can use only 2^32 bytes, i.e., 4 GB, of memory --- unless one uses pae(4). Some of the 2^32 addresses are used by devices like the video card, and by the BIOS. For instance, if the machine has a video card with 512 MB of video RAM, this means that less than 3.5 GB of memory can be used. It seems a safe bet in such a case to install at most 3 GB of memory. There is more info at http://www.codinghorror.com/blog/archives/000811.html http://en.wikipedia.org/wiki/Memory_address Raghavendra. -- N. Raghavendra | http://www.retrotexts.net/ Harish-Chandra Research Institute | http://www.mri.ernet.in/ See message headers for contact and OpenPGP information.