Relatedly, why is PCIe x16, say, faster than PCIe x1? What functions are the extra pins performing if data cannot be sent multiple bits at a time?
In: Engineering
I can’t speak to HDMI, but PCIe I know.
The simple answer is the analog of water passing in a pipe. Just as the water in a pipe goes 1 part of water (cross-section area) in series at a time if you watched closely. The simple difference of x16 vs. x1 is that you have a pipe with 16x the diameter vs. “1x” or “normal” diameter. Similar to how a fire hydrant is a very wide pipe, but a bathroom sink is a narrow pipe. Pipes allow water to flow in a straight line, with varying widths.
Why is this useful? Some PCIe uses are for graphics cards that need that x16 diameter pipe to display your mind-blowing videos. Some use cases are just a slow wifi adapter that can use x2 or x4 because the pipe requirements don’t need as much “water” or “information” all at once.
Getting deeper, PCIe was invented for flexible use cases that were unforeseen at creation. They allowed a way for future uses to continue with the same interface for ease of computer design re-use (i.e. processor design re-use).
Yes, it is a “serial interface” – but it’s actually complex and using all those pins in parallel too. It’s actually a configurable set of “serial interfaces” in “parallel configuration”. If you need to know the details of a serial interface, it simply means that the data contains the clock embedded in the data signal itself. There is a “PCIe Clock” signal, but that isn’t for data collection, just coordination at the low-level and proper reference alignment to ensure the 2x processors that are talking to each other know what is going on. The details are scary, so just reply if you must know.
A real system has Processor <-> PCIe <-> Graphics Card (w/ Processor) <-> HDMI <-> Monitor
Another example is Processor <-> PCIe <-> Wi-Fi Client (w/ Processor) < – – air – – > Wi-Fi Access Point (w/ Processor) <-> Cable/Fiber/ (puke) DSL
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