I was studying the I/O process of a PC...and I think I understood it..but not very much so I will type what I understood giving an example..and I hope that I got it right

e.g. typing with a keyboard

First: The Input, and that is done simply by the keyboard..

Second: The information gets to the CPU in binary, but the logic unit doesn't understand it so the Control Unit gets the Instructions saved in the RAM by the CU it self.. then the instructions is sent to the Logic Unit through the CU

Finally:The Logic Unit understands it that time and do some operations that produces some Outputs. The outputs are saved in the RAM, and viewed on the screen

So, please tell me if that's right or if I missed the whole thing.. Thank you very much in advance.

  • $\begingroup$ I'm not sure if this is ontopic here. Community votes, please! $\endgroup$
    – Raphael
    Jul 12, 2016 at 21:24
  • $\begingroup$ @Raphael. Seems on-topic to me. $\endgroup$ Jul 12, 2016 at 23:13
  • 1
    $\begingroup$ Have you seen topic about echoing? Or this one about peripherials? Might be helpful, but now back to your question - could you specify it? Besides the title there is none, and it seems very broad right now. Also there are some assumptions, like CU saves instruction in RAM, are you sure this is the case? $\endgroup$
    – Evil
    Jul 12, 2016 at 23:27
  • $\begingroup$ @Evil No sir, I just wrote what i could understand from hours of reding things about receiving, processing and outputing. So I'm asking if what I understood is right. And if not can you explain it to me. And the topics you mentioned won't help me, as I'm not even sure how the process is done. $\endgroup$ Jul 12, 2016 at 23:46
  • $\begingroup$ @TalalSharaa Questions of this form work well with a teacher or friend, but not so well on this website. Specific questions with clear-cut answers work best. Can you formulate any such question? $\endgroup$
    – Raphael
    Jul 13, 2016 at 8:10

2 Answers 2


From what I know, and I might be slightly wrong here, each device (Mouse, keyboard, screen etc') has a device driver.

The device driver is the one handling the communications with the CPU. Where usually, each device has its own Data register, Status register and Command register (Where the register are basically mapped areas in memory for the device itself).

What happens is when any action is made (i.e pressing a key on the keyboard) the device "updates its status" to ready to send and stores the data it needs to send in some area of memory specifically saved for it, and then interrupts the CPU to perform the action needed.

The CPU sends "Ack" as acknowledgement and accepts the interrupt, executes it, and goes back to what it did before. (Only if the status is ready, otherwise does nothing).

(There are other methods such as busy wait that the device can notify and interact with the CPU).


An easy way to facilitate understanding the working of a CPU is using the Little Man Computer which provides a visual representation of how instructions are processed to manipulate data. You can find it here http://peterhigginson.co.uk/LMC it may be useful to go through the help section to facilitate understanding. Note that this is a simple model. Good luck.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.