From owner-freebsd-hardware Tue Dec 11 10:56:22 2001 Delivered-To: freebsd-hardware@freebsd.org Received: from warspite.cnchost.com (warspite.concentric.net [207.155.248.9]) by hub.freebsd.org (Postfix) with ESMTP id 45F9F37B419 for ; Tue, 11 Dec 2001 10:56:19 -0800 (PST) Received: from bitblocks.com (adsl-209-204-185-216.sonic.net [209.204.185.216]) by warspite.cnchost.com id NAA26541; Tue, 11 Dec 2001 13:55:43 -0500 (EST) [ConcentricHost SMTP Relay 1.14] Message-ID: <200112111855.NAA26541@warspite.cnchost.com> To: nate@yogotech.com (Nate Williams) Cc: 9ustavo 9onzalez 9iron , freebsd-hardware@FreeBSD.ORG Subject: Re: i286 In-reply-to: Your message of "Tue, 11 Dec 2001 11:23:33 MST." <15382.20261.860671.461839@caddis.yogotech.com> Date: Tue, 11 Dec 2001 10:55:43 -0800 From: Bakul Shah Sender: owner-freebsd-hardware@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org > As I understand, don't you need paging for 'real' protection to work > right, otherwise you're limited to one/two processes on the box? Use of a page table to map a virtual address VA to a physical address PA is the most common method but not the only one. In the extreme case all you need is hardware that can do: PA = contents of a base_register + VA As long as the base register is not visible to user mode programs and the phys addr range for different processes didn't overlap, your process is protected! Actually, you don't even need virtual address space; just protectable address ranges (something you can do in i286) so that a process can only access address ranges open to it but this is not useful except for specialized closed system. The common method was in early 80s was to use two to four segments: code, initialized data, bss and stack. When you needed to make space for a new process, you swapped out an old process to disk instead of a few pages. This is how Unix upto V7 and, I believe also, system 3 (SVR3) worked. Please look up the Unix history for details. -- bakul To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hardware" in the body of the message