Components for Building Computers From Scratch/PC BUS


QUESTION: I know all slow Devices like IDE and PCi and Floppy Drive and SATA all use the Southbridge to Conect to the Northbridge.

And yes I know the new CPUs have the Northbridge zBuilt into them.

But what I need help understanding is if you have a Motherboard that has standard PCi Slots that run at 133Mbps.

And it is conected to the Southbridge I get this but if you have say IDE for your Hard Drive as well.

I know PCi Slots run at diferant speeds then IDE so does it matter what speed the Southbridge runs at because you can have a fast Southbridge speed but if you are getting Data from a PCi Slot that runs at 133Mbps.

It does not matter how fast the Southbridge runs at am I right?

ANSWER: I'm not fully understanding your question - in a "conventional" system with a CPU that connects to the Northbridge (or "Memory Controller Hub" (MCH for short) via an FSB, and which also has a Southbridge (or "I/O Controller Hub" (ICH for short), there is a high-speed link between the MCH and ICH, and the ICH provides sufficient bandwidth for the PCI bus (133MB/s (not Mb/s) aggregate), as well as other peripherals it connects (e.g. ATA-133, USB2.0, etc). The MCH will also provide AGP or PCI Express connectivity, if featured.

On newer systems the CPU generally contains the memory controller, and in some cases also the graphics controller and other functionality, and it interfaces directly to the RAM and the ICH via high-speed link. The ICH concept remains more or less the same, but in more modern systems they tend to provide more bandwidth and connectivity (for example they can provide additional PCI Express lanes, USB3.0 support, and so on).

The "speed" of the MCH and ICH should be assumed sufficient for the tasks they're designed to complete - many years ago it wasn't uncommon to find comparisons between different models of motherboard, often with very real performance differences able to be observed depending on their hardware layout. However in recent years this has become less of a concern, as things have both standardized and integrated - performance differences between motherboards are generally very small (if measurable), and differences between different chipset models are often equally small (usually the delineating factors these days are I/O capabilities, not I/O performance).


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QUESTION: Well if you have a Motherboard and it has PCi 133MBps Slots and SATA Interfaces.

They conect to the Southbridge. And the Southbridge speed is a speed all by itself.

So if a PCi Slot send Data at just say 133MBps andd the Southbridge is say Faster then this what happens?

I always thought about this because everything runs at diferant speeds?

ANSWER: The PCI bus has 133MB/s between it and the ICH; if the ICH has an integrated SATA controller that will interface at whatever speed it provides to the drives. They're separate interfaces. On some motherboards the SATA controller is "external" (a separate chip on the board), and is often connected through the PCI bus (so it shares with that 133MB/s bandwidth, just like a PCI SATA card would).

Perhaps an illustration would help, here's a block diagram for the Intel 875p platform, which uses a conventional MCH/ICH arrangement, and is designed to work with the Pentium 4 CPU:

In theory it may be possible to over-saturate the ICH/MCH link, however in practice this is not likely to occur, as most hard-drives will not actually operate fast enough to reach the theoretical limit of their connection (and are not always reading/writing at their maximum transfer limit), and most peripheral devices also do not consume all of their available bandwidth constantly. Generally different peripherals will be used at different times based on user activity, for example you wouldn't likely be playing a demanding 3D videogame while also downloading hundreds of pictures from your digital camera and rendering hours of digital video all at once. You'd more likely do one of those activities at a time, which will use different sections of the computer to different extents (if you did all three things at once it would likely work, but everything would likely run more slowly than if it were handled individually).


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QUESTION: I think I get what you are telling me.

If I have say 4 PCi Slot that run at 133MBps all 4 Slot will split up the Bandwidth.

And if I have a SATA Interface my SATA will be useing the Southbridge as well as the PCi Slots.

And my SATA and PCi Slot will all be splitting up the Southbridge BUS bandwidth.

So say I am playing sound through a PCi Sound Card and I am transfering Data from my SATA Drive to another SATA Drive.

My SATA Drives will be slitting up the same Bandwidth.

Do I have this right I think I understand you now?

Yes and no. The PCI bus shares bandwidth, but if the system has multiple busses (usually this is seen if you have PCIe->PCI bridges) each bus gets its own bandwidth. If the SATA controller is on the PCI bus it will also share from that bandwidth pool, but if it's part of the ICH it won't necessarily share from that bandwidth. Each SATA device, at least in theory, has full bandwidth (for whatever version of SATA it uses) between it and the controller, however in practice this will be limited by the drive's speed (in most cases the interface is faster than the drive, to prevent the interface from being a bottleneck to the drive) and what the controller can handle internally (it may not be capable of handling 8x150 or 8x300 simultaneously, for example, but handling 2x150 or 2x300 may work just fine) - look for benchmark reviews of SATA controllers and hard-drives for more specific information about this.


Components for Building Computers From Scratch

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