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From Wikipedia:

Wikipedia screengrab

I was wondering how to understand the right-down corner of the picture?

Are SATA,USB, Ethernet, mouse, keyboard, and serial/parallel ports connected to Southbridge via PCI bus? In other words, are the buses from Southbridge and Super I/O to "Cables and ports leading-off board" PCI buses?

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The used picture is outdated. Today Intel as well as AMD system don't have a Northbridge anymore. It is integrate into the CPU. – Robert Aug 21 '12 at 8:19
up vote 2 down vote accepted

Are SATA,USB, Ethernet, mouse, keyboard, and serial/parallel ports connected to Southbridge via PCI bus? I

No those items are only connected to the southbridge and super-io chips

are the buses from Southbridge and Super I/O to "Cables and ports leading-off board" PCI buses?

The lines to "cables and ports ..." are the respective rs232, USB etc types of electrical connection, not PCI

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Thanks! Are USB ports really directly connected to southbridge without PCI bus in between, as shown in the picture? Why in the output of udevadm info -a -n /dev/sdb for an external USB 2.0 HDD connected to a laptop, there is an item for PCI (see here)? – Tim Aug 21 '12 at 14:07
    
@Tim, For example, see block diagram on P12 of manual for AMD SB710. Details depend on chipset used on motherboard. Note "A-Link Express and A-Link Express II are essentially PCIe 1.1 x4 lanes." according to Wikipedia but this isn't the bus used for PCI slots. – RedGrittyBrick Aug 21 '12 at 15:57
    
Thanks! Not sure what I should look at in the diagram. (1) Is "PCI bridge" the southbridge? (2) Do you mean for some, USB ports are directly connected to southbridge without a PCI, and for others, there is a PCI bus in between? – Tim Aug 21 '12 at 16:06
    
@Tim: the whole thing is the southbridge chip. The PCI-bridge is a small area of circuitry on the southbridge chip. There is no single masterplan for computers, each chipset and motherboard has it's own way of doing things. – RedGrittyBrick Aug 21 '12 at 16:11
    
USB host controllers are PCI(-E) devices, even if they are integrated into the "southbridge". (In quotes because that name is becoming obsolete, but there's still a functional equivalent.) The "Super I/O chip" shown above is attached to the "LPC", Low Pin Count, bus. This is a seven-wire (minimum) serial bus that logically emulates the old ISA bus. LPC in turn is supported by a PCI to LPC bridge, was is also inside the "southbridge". – Jamie Hanrahan May 8 '15 at 1:12

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