Date: Thu, 28 Feb 2008 05:45:23 +1100 From: Peter Jeremy <peterjeremy@optushome.com.au> To: Jeff Isaac <cineveggie.lists@gmail.com> Cc: freebsd-amd64@freebsd.org Subject: Re: "freebsd-amd64" Message-ID: <20080227184522.GE83599@server.vk2pj.dyndns.org> In-Reply-To: <443D814E-04F3-411C-9DF9-E799A39FAEB3@gmail.com> References: <E1JULcb-0001Er-9m@dilbert.ticketswitch.com> <443D814E-04F3-411C-9DF9-E799A39FAEB3@gmail.com>
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--k1BdFSKqAqVdu8k/ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Feb 27, 2008 at 07:34:48AM -0600, Jeff Isaac wrote: >doodle with, not BIOS), BUT, from a general knowledge perspective, what=20 >advantages does virtual 86 mode have over real mode? Essentially, why did= =20 >the FreeBSD project choose the virtual implementation? More portable?=20 >Easier to write? None of the above? Thanks! :) The kernel run in 32-bit protected mode. Switching between protected mode and real mode requires a reasonable degree of voodoo which does not currently exist in the kernel (the loader handles the initial real to protected transition and the kernel then never leaves protected mode). Plus you need to either ensure that exceptions/interrupts won't occur or handle them in real mode. OTOH, virtual86 mode is part of the hardware - you create a task descriptor and set the VM86 bit. Any exceptions etc are delivered to the kernel. --=20 Peter Jeremy Please excuse any delays as the result of my ISP's inability to implement an MTA that is either RFC2821-compliant or matches their claimed behaviour. --k1BdFSKqAqVdu8k/ Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.4 (FreeBSD) iD8DBQFHxa/C/opHv/APuIcRAgUeAKCTVGSNOk0mTV6OpXPdRpkg8BOVqgCfcR3q SmeCq7J+0bGmjJ8EuWiITWg= =dowN -----END PGP SIGNATURE----- --k1BdFSKqAqVdu8k/--
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