Athlon 64/Opteron boards without Southbridge?

[n0d3]

Hi,

I was just wondering how you guys feel about a motherboard without a southbridge. The reason why i'm wondering about this is nowadays we have mobo's getting clutterd up with too much, and unnesasery stuff. Especially for some users. For instance, 6 USB ports, built in audio/lan/etc. Some people I do thik prefer their own hardware. Lets say a SB instead of the onboard sound and a 3com/or better instead of an onboard realtek, and why not get one of those USB/Fireware combined cards instead of having 6 built in USB ports. Oh and who needs onboard ata/133 when alot of boards these days have secundary raid controllers onboard.

Now with the comming of the opterons and PCI-Express, as far as I understood the PCI-express 'plugs' right into the Northbridge so what really is the use of the SB then? I wonder then if it would be possible to have a sb-less mobo and have all hardware in pci(express) form. That way you could choose your own Sound card and you wouldn't have to pay for the SB and all the extra traces that come with that. As far as I understand it PCI-Express is a serial bus and the old pci standard will be backwardly supported so it also communicates then over the pci-express serial bus so there should be a bunch of those on there for the extra cards needed.

I doubt thought anything like that would ever happen because if that would be possible it would have been done by now. So let us know how you feel think about this.

P.S. anybody happen to know if there's finally gonna be more IRQ's with the athlon 64/opteron or are we still stuck with only 16, and also will the pci-express bus just use one IRQ for it's entire bus or will each device have a seperate IRQ (wich shouldn't be nesaserry since it's on a serial bus (see scsi?)

 

[Vette73]

Actually the Athlon64/Opterons will be getting rid of the northbridge. The memory controller is built into the CPU. So only the AGP connect remains. And if you have something on the board that is not inside the southbridge, it will have ti run on the PCI bus.

And the ethernet card built into the nForce2 southbridge outperforms and uses less cpu cycles then 3coms ethernet card. It was one of the things that was pointed out when anandtech.com did a early review of the nForce2 board. The MCP-T southbridge has a Nivida and 3com ethernet card built into it, and the 3com was not as good as the nivida one.

 

[n0d3]

It was only a mear example. Say you'd want a nother, better, performing card in there etc. And yes, the Opteron does get rid of the memory controller (allthough they are still in the NB) the NB also has your pci-express connect in it no? It used to house the AGP bus but that's gonna be a goner aswell.

But it's still confusing though. Let's look at the nForce3 Pro's diagram (http://firingsquad.gamers.com/hardware/nforce3_pro/page2.asp) It seems to me that this 'once chip sollution' is connected through the hypertransport bus directly to the CPU. Since it has no PCI-express connectivety you only get PCI support through this chip. With all it's 'extra' features. Looking at the K8T400's diagram (http://www.extremetech.com/article2/0,3973,1148433,00.asp) we clearly see a NB SB design. However it seems to me that the NB is simply a AGP addon part and doesn't do much. Aswell as it's lacking of PCI-EXPRESS.

I guess we'll have to see how things will go but it would be nice to see some more 'barebone' motherboards as there are plenty of people who disable onboard equipment for whatever reason.

 

[Peter]

If you'd leave out the southbridge, it wouldn't be an IA32 (read Windows) compatible machine anymore. The SB not only contains lots of I/O, but also important core bits like the interrupt controller, system timers, as well as a bus bridge over to the remains of the ISA bus where we have more IA32 essentials like the keyboard controller and RTC.
Leave out just one of those, and it won't be a compatible PC anymore.

 

[Peter]

n0d3, everyone except NVidia is making north bridges that do three things - connect to CPU via HT, bridge to AGP, and bridge to their proprietary southbridge bus. This is to leverage the existing south bridges to the Opteron platform.
NVidia made a complicated new chip, essentially a south bridge with an AGP bridge in it. (Since they've always used HyperTransport for their north-south connection, they've already had the technology in the SB.)

 

[n0d3]

well back in the old days we used to have ISA and later PCI peripials to do those jobs. Think ISA IDE controllers etc. There used to be no Southbridges I don't think. So I guess it's just wishfull thinking on getting a sb less system. I'm kinda not wanting to get a nVidia nForce solution because they seem to be optimizing for the quadro on the AGP making me wonder how performance is diffrent with diffrent (ATi) cards. It wouldn't come to a suprise to me if ATi's would for some odd reason perform just a little less ...

And I do remember VIA's IDE implementation beeing somewhat slower then for instance, intel's. But there probably be many reviews etc by the time I'm ready to get a new rig, somwehere in march (2nd generation A64's)

 

[Peter]

Where'd you think the ISA bus came from? Right. Southbridge. The ISA bus, technically, is still there - only that all the legacy system core crap has been pulled into the SB chip, and the legacy peripheral I/O is on a pin-count-reduced "LPC" incarnation of ISA.
Only waaaaaay back when everything was ISA and there was neither PCI nor local bus nor EISA, the north bridge directly issued an ISA bus.

The best IDE implementation currently is in SiS chipsets, thanks to their massively fast chipset internal busses. VIA's new 8237 south also seems to be quite a bit faster than their previous solutions, mainly because they doubled the I/O link speed up to the north bridge.
Intel's chipsets still have the south bridge on a 266 MB/s connection, while VIA and SiS are on a 1 GB/s wire now. nVidia uses a HyperTransport link at either 400 or 800 MB/s.