Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261370AbTHSUjw (ORCPT ); Tue, 19 Aug 2003 16:39:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261380AbTHSU2z (ORCPT ); Tue, 19 Aug 2003 16:28:55 -0400 Received: from hq.pm.waw.pl ([195.116.170.10]:12775 "EHLO hq.pm.waw.pl") by vger.kernel.org with ESMTP id S261406AbTHSUTR (ORCPT ); Tue, 19 Aug 2003 16:19:17 -0400 To: Jamie Lokier Cc: Paolo Ornati , linux-kernel@vger.kernel.org Subject: Re: [OT] Documentation for PC Architecture References: <200308181127.43093.javaman@katamail.com> <20030818185507.GB8297@www.13thfloor.at> <200308182244.01727.javaman@katamail.com> <20030818225422.GA23927@www.13thfloor.at> <20030819010205.GE11081@mail.jlokier.co.uk> From: Krzysztof Halasa Date: 19 Aug 2003 17:23:21 +0200 In-Reply-To: <20030819010205.GE11081@mail.jlokier.co.uk> Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1418 Lines: 26 Jamie Lokier writes: > Paolo's question is, what happens to the 384k of _physical_ addresses > starting at 0xa0000, which should correspond with 384k of actual > physical RAM? Part of it is used for BIOS (shadow of EPROM/flash EPROM - usually written by BIOS executing from EPROM and then made read-only by programming chipset registers). This involves main motherboard BIOS (usually 64 KB at 0xF000-0xFFFF) and any extension BIOSes (VGA, LAN etc) in 0xC000-0xEFFF (or 0xC000-0xDFFF) range. The remaining RAM from 0xA000-0xFFFF is unusable. One could program chipset registers to enable parts of this RAM. It would require knowledge of particular chipset registers, and there might be only one read-only/read-write bit for all shadows (so, unless you want the shadow BIOS to be R/W, the additional RAM would have to be R/O). RAM is quite cheap and these things are very non-standard so I think nobody bothers. And yes, older machines (older chipsets) used to remap fragments of this memory to the top of RAM. It was common on 80286 machines and I probably haven't seen a 386DX or faster board doing that. -- Krzysztof Halasa Network Administrator - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/