Meaning of “expansion bus” or “peripheral bus”

Question

From my last post "expansion bus" and "peripheral bus", "expansion bus" or "peripheral bus" are said to be the same concept. My questions here are not the same as those before. Please do read both of them, before you judge.

1. From the Wikipedia article "Expansion bus", expansion bus is defined as:

   An expansion bus is made up of electronic pathways which move information between the internal hardware of a computer system (including the CPU and RAM) and peripheral devices. It is a collection of wires and protocols that allows for the expansion of a computer.

   As far as I know peripheral devices can be internal or external to the computer case. So I wonder if here peripheral devices mean external peripherals only?

2. What is the opposite concept of "expansion bus" or "peripheral bus"?

3. In the following image, what buses are "expansion bus" or "peripheral bus"?

   

Thanks!

Answer 1

The answer to your question lies in the Wikipedia articale about peripheral devices you linked to:

A peripheral is a device connected to a host computer, but not part of it. It expands the host's capabilities, but does not form part of the core computer architecture. It is often, but not always, partially or completely dependent on the host.

A peripheral is generally defined as any auxiliary device such as a computer mouse, keyboard, hard drive, etc. that connects to and works with the computer in some way. Other examples of peripherals are Expansion cards, graphics cards, computer printers, image scanners, tape drives, microphones, loudspeakers, webcams, and digital cameras. RAM - random access memory - straddles the line between peripheral and primary component; it is technically a storage peripheral, but is required for every major function of a modern computer and removing the RAM will effectively disable any modern machine.

As you can see, internal and external don't refer to the computer case, but to the core computer architecture. As a rule of thumb, anything that can be removed without damaging the computer of preventing it from booting up isn't part of it's core architecture and – therefore – peripheral.

The "opposite" of an expansion bus would be an internal bus, such as those between CPU and Northbridge, Northbridge and Southbridge, CPU and chipset (all if present) or the memory bus.