Date: Mon, 2 Aug 1999 21:12:38 -0700 (PDT) From: Brian McGroarty <bvmcg@yahoo.com> To: "Louis A. Mamakos" <louie@TransSys.COM>, Doug Ambrisko <ambrisko@whistle.com> Cc: multimedia@FreeBSD.ORG Subject: Re: 3D board for XFree86 GLX - Please recommend Message-ID: <19990803041238.12562.rocketmail@web1006.mail.yahoo.com>
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I don't know anything about the UNIBUS - what was the concept there? For passive components, there's pretty much no difference between AGP and PCI. With the early video cards, they pretty much put different connecters on the cards to be able to sell an AGP card as soon as possible. With newer cards, some of the main advantages are: Shorter prologs/epilogs for DMA operations - this allows more effective scatter gather operations. Of AGP, PCI, RAM and the CPU, two pairs of two can be communicating with each other at once - this means AGP can talk to RAM while the CPU is bothering itself with PCI components. Ditto AGP and PCI communicating while the CPU's banging on RAM. AGP can transfer data on the rise and fall of a clock cycle - 66mhz * 64 bit * 2 xfers. (I'm not sure how widely implemented this last is.) --- "Louis A. Mamakos" <louie@TransSys.COM> wrote: > > Doug Rabson writes: > > | On Sun, 1 Aug 1999, Marc van Woerkom wrote: > > | > Possible. AGP bandwith is 2x or 4x of PCI. > > | AGP is 2x or 4x 32bit PCI at 33Mhz. 64bit PCI at 66Mhz > matches AGP speeds > > | without reinventing the wheel... > > > > Yep, I hate AGP ... my guess is Intel had trouble making a > real PCI slot > > work like it is supposed to so they invented AGP so they > only had to > > make one separate PCI slot work. > > Well, there is a bit more to it than that. I think the AGP > slot (and > associated support chips) also include a mapping capability so > that the > AGP peripheral can do DMA bus cycles to virtual addresses you > hand to > it. This could be handy so that you don't need contiguous > physical > memory for texture maps, etc. > > Of course I'm sure this is some new invention, totally unlike > the > UNIBUS mapping registers we used in the dark ages. _____________________________________________________________ Do You Yahoo!? Free instant messaging and more at http://messenger.yahoo.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-multimedia" in the body of the message
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