From owner-freebsd-questions@FreeBSD.ORG Thu Nov 17 20:50:26 2005 Return-Path: X-Original-To: freebsd-questions@freebsd.org 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 27EC116A422 for ; Thu, 17 Nov 2005 20:50:26 +0000 (GMT) (envelope-from cswiger@mac.com) Received: from pi.codefab.com (pi.codefab.com [199.103.21.227]) by mx1.FreeBSD.org (Postfix) with ESMTP id 6275643D62 for ; Thu, 17 Nov 2005 20:50:24 +0000 (GMT) (envelope-from cswiger@mac.com) Received: from localhost (localhost [127.0.0.1]) by pi.codefab.com (Postfix) with ESMTP id 259AA5FA8; Thu, 17 Nov 2005 15:50:23 -0500 (EST) Received: from pi.codefab.com ([127.0.0.1]) by localhost (pi.codefab.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 16370-07; Thu, 17 Nov 2005 15:50:21 -0500 (EST) Received: from [192.168.1.3] (pool-68-161-122-227.ny325.east.verizon.net [68.161.122.227]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by pi.codefab.com (Postfix) with ESMTP id DAED85CB2; Thu, 17 Nov 2005 15:50:20 -0500 (EST) Message-ID: <437CED0D.2080800@mac.com> Date: Thu, 17 Nov 2005 15:50:21 -0500 From: Chuck Swiger Organization: The Courts of Chaos User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.12) Gecko/20050915 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Dan Nelson References: <20051117150323.U1019@ganymede.hub.org> <437CE254.3080701@mac.com> <20051117202734.GF62141@dan.emsphone.com> In-Reply-To: <20051117202734.GF62141@dan.emsphone.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: amavisd-new at codefab.com Cc: "Marc G. Fournier" , freebsd-questions@freebsd.org Subject: Re: EM64T supported? X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 17 Nov 2005 20:50:26 -0000 Dan Nelson wrote: > In the last episode (Nov 17), Chuck Swiger said: >>EM64T uses 64-bit wide registers and addressing, and can talk to >4GB >>of RAM natively. Older processors may still support >4GB of physical >>RAM using the PSE/PSE-36 CPU extensions, but are still using 32-bit >>registers. > > PAE/PAE36, right? Note that if you enable PAE, some drivers may not be > available. See the PAE kernel config file for a list. PAE is related, but I don't believe "PAE36" exists; cpuid lists these: PSE Page Size Extensions PAE Physical Address Extension PSE-36 36-bit Page Size Extension I believe PSE lets you choose whether your MMU uses a 4KB or a 4MB pagesize for virtual address translation. PAE was the first attempt at supporting more than 4GB of address space, but I gather it requires doing bank swapping or something fairly awkward that doesn't play too well with VM, whereas PSE-36 integrates more easily. The other point you've made is correct, that is, a fair number of drivers don't understand PAE/PSE36 yet, and will not work using it-- generally because the hardware associated with the driver has a DMA engine which is limited to 32-bit addressing. You end up having to double-buffer or use "DMA bounce buffers", whatever phrase you wish to use. :-) This link seems to have a more complete description: http://www.microsoft.com/whdc/system/platform/server/PAE/pae_os.mspx -- -Chuck