title: What is the difference between Memory and IO bandwidth and how do we measure each one?
body: <p>What is the difference between memory and io bandwidth, and how do you measure each one?</p>
  
  <p>I have so many assumptions, forgive the verbosity of this two part question.</p>
  
  <p>The inspiration for these questions came from: <a href="https://stackoverflow.com/questions/57133871/what-is-the-meaning-of-ib-read-ib-write-ob-read-and-ob-write-they-came-as-out#57135393">What is the meaning of IB read, IB write, OB read and OB write. They came as output of Intel&#174; PCM while monitoring PCIe bandwidth</a> where Hadi explains:</p>
  
  <p><code> DATA_REQ_OF_CPU </code> is NOT used to measure memory bandwidth but i/o bandwidth.</p>
  
  <p>I’m wondering if the difference between mem/io bandwidth is similar to the difference between DMA(direct memory addressing) &amp; MMIO(memory mapped io) or if the bandwidth of both IS io bandwidth?</p>
  
  <p>I’m trying to use this picture to help visualize:</p>
  
  <p><a href="https://i.stack.imgur.com/ViZEI.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ViZEI.gif" alt="enter image description here"></a></p>
  
  <p>(Hopefully I have this right) In x86 there are two address spaces: Memory and IO. Would IO bandwidth be the measure between cpu (or dma controller) to the io device, and then memory bandwidth would be between cpu and main memory? All data in these two scenarios running through the memory bus? Just for clarity, we all agree the definition of the memory bus is the combination of address and data bus? If so that part of the image might be a little misleading...</p>
  
  <p>If we can measure IO bandwidth with Intel® Performance Counter Monitor (PCM) by utilizing the pcm-iio program, how would we measure memory bandwidth? Now I’m wondering why they would differ if running through the same wires? Unless I just have this all wrong. The github page for a lot of this test code is a bit overwhelming: <a href="https://github.com/opcm/pcm" rel="nofollow noreferrer">https://github.com/opcm/pcm</a> </p>
  
  <p>Thank you </p>