This text below is hard to understand. Some thing that the PCIe uses 10 bits to send 8 bits because it is a serial bus that it cannot send 8 bits.
Why the computer bus cannot send 8 bits because some thing to do with it being a serial bus or clock.
Quote PCIe is a serial bus with the clock embedded in the data, it needs to ensure that enough level transitions (1 to 0 and 0 to 1) occur for a receiver to recover the clock. To increase level transitions, PCIe uses “8b/10b” encoding, where every eight bits are encoded into a 10-bit symbol that is then decoded at the receiver. Thus, the bus needs to transfer 10 bits to send 8 bits of encoded data. Quote
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What is the difference between sending zeros and not setting anything at all of you just send the data on a serial bus?
You can do that on a parallel bus because there is a separate clock line and you can add a specific line that says I am sending data. But on a serial line that is independent how do you know that anything is sent if there are just zeros?
The answer is you need to ensure that any message you send includes both zeros and ones. You also need the often enough changes from zero to one or the other way to determine the clock of the signal. So if you change 8 bits of data to 10 bites on the line you can create a signal that always includes both 1 and 0 and changes often enough to recover the clock.
There is a reason you have a serial signal with the clock built into the signal instead of a separate clock and data line like in a parallel bus.
How fast an electric signal propagates depend on its surrounding. It is hard to build many parallel wires where all signals travel at the same speed. There will be some variation in the arrival time of the signal. When you send data so fast that the variation in arrival time is comparable to the length of bits there will be lots of errors because the value of the line has not yet changed.
It is simple to have all lines as separate serial lines that operate at a bit higher clock speed so you can send 10 bits for 8 bits of data compared to trying to make electronics where all signals arrive at the same time.
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