How can a computer run an infinite loop?










5














I understand the concept behind for and do/while loops, but I am trying to understand what is happening at the hardware level that allows a loop to run infinitely. Technically wouldn't it have to stop at some point because there are only a couple billion transistors in a microprocessor? Maybe my logic is off.










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  • 4




    A mechanical counter can only memorize a few digits, but it can loop forever. After 9999, we restart from 0000. Your argument only proves that in an infinite computation, the processor will eventually visit the same state twice, entering a loop.
    – chi
    Nov 9 '18 at 17:33






  • 2




    See this comment.
    – philipxy
    Nov 9 '18 at 19:58







  • 5




    "only a couple billion transistors". The same transistors get used over and over while the processor is running.
    – Barmar
    Nov 9 '18 at 20:23






  • 9




    A running track has a finite size, but you can run around it as many times as you like.
    – Barmar
    Nov 9 '18 at 20:24






  • 1




    A Cray can finish an infinite loop in 3 seconds.
    – kelalaka
    Nov 12 '18 at 16:04















5














I understand the concept behind for and do/while loops, but I am trying to understand what is happening at the hardware level that allows a loop to run infinitely. Technically wouldn't it have to stop at some point because there are only a couple billion transistors in a microprocessor? Maybe my logic is off.










share|cite|improve this question



















  • 4




    A mechanical counter can only memorize a few digits, but it can loop forever. After 9999, we restart from 0000. Your argument only proves that in an infinite computation, the processor will eventually visit the same state twice, entering a loop.
    – chi
    Nov 9 '18 at 17:33






  • 2




    See this comment.
    – philipxy
    Nov 9 '18 at 19:58







  • 5




    "only a couple billion transistors". The same transistors get used over and over while the processor is running.
    – Barmar
    Nov 9 '18 at 20:23






  • 9




    A running track has a finite size, but you can run around it as many times as you like.
    – Barmar
    Nov 9 '18 at 20:24






  • 1




    A Cray can finish an infinite loop in 3 seconds.
    – kelalaka
    Nov 12 '18 at 16:04













5












5








5


3





I understand the concept behind for and do/while loops, but I am trying to understand what is happening at the hardware level that allows a loop to run infinitely. Technically wouldn't it have to stop at some point because there are only a couple billion transistors in a microprocessor? Maybe my logic is off.










share|cite|improve this question















I understand the concept behind for and do/while loops, but I am trying to understand what is happening at the hardware level that allows a loop to run infinitely. Technically wouldn't it have to stop at some point because there are only a couple billion transistors in a microprocessor? Maybe my logic is off.







loops control-flow






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share|cite|improve this question













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share|cite|improve this question








edited Nov 11 '18 at 19:50









Bergi

34519




34519










asked Nov 9 '18 at 9:21









Cody Rutscher

498




498







  • 4




    A mechanical counter can only memorize a few digits, but it can loop forever. After 9999, we restart from 0000. Your argument only proves that in an infinite computation, the processor will eventually visit the same state twice, entering a loop.
    – chi
    Nov 9 '18 at 17:33






  • 2




    See this comment.
    – philipxy
    Nov 9 '18 at 19:58







  • 5




    "only a couple billion transistors". The same transistors get used over and over while the processor is running.
    – Barmar
    Nov 9 '18 at 20:23






  • 9




    A running track has a finite size, but you can run around it as many times as you like.
    – Barmar
    Nov 9 '18 at 20:24






  • 1




    A Cray can finish an infinite loop in 3 seconds.
    – kelalaka
    Nov 12 '18 at 16:04












  • 4




    A mechanical counter can only memorize a few digits, but it can loop forever. After 9999, we restart from 0000. Your argument only proves that in an infinite computation, the processor will eventually visit the same state twice, entering a loop.
    – chi
    Nov 9 '18 at 17:33






  • 2




    See this comment.
    – philipxy
    Nov 9 '18 at 19:58







  • 5




    "only a couple billion transistors". The same transistors get used over and over while the processor is running.
    – Barmar
    Nov 9 '18 at 20:23






  • 9




    A running track has a finite size, but you can run around it as many times as you like.
    – Barmar
    Nov 9 '18 at 20:24






  • 1




    A Cray can finish an infinite loop in 3 seconds.
    – kelalaka
    Nov 12 '18 at 16:04







4




4




A mechanical counter can only memorize a few digits, but it can loop forever. After 9999, we restart from 0000. Your argument only proves that in an infinite computation, the processor will eventually visit the same state twice, entering a loop.
– chi
Nov 9 '18 at 17:33




A mechanical counter can only memorize a few digits, but it can loop forever. After 9999, we restart from 0000. Your argument only proves that in an infinite computation, the processor will eventually visit the same state twice, entering a loop.
– chi
Nov 9 '18 at 17:33




2




2




See this comment.
– philipxy
Nov 9 '18 at 19:58





See this comment.
– philipxy
Nov 9 '18 at 19:58





5




5




"only a couple billion transistors". The same transistors get used over and over while the processor is running.
– Barmar
Nov 9 '18 at 20:23




"only a couple billion transistors". The same transistors get used over and over while the processor is running.
– Barmar
Nov 9 '18 at 20:23




9




9




A running track has a finite size, but you can run around it as many times as you like.
– Barmar
Nov 9 '18 at 20:24




A running track has a finite size, but you can run around it as many times as you like.
– Barmar
Nov 9 '18 at 20:24




1




1




A Cray can finish an infinite loop in 3 seconds.
– kelalaka
Nov 12 '18 at 16:04




A Cray can finish an infinite loop in 3 seconds.
– kelalaka
Nov 12 '18 at 16:04










5 Answers
5






active

oldest

votes


















25














step 1: take a calculator



step 2: input a number



step 3: add 1 to the number



step 4: subtract 1 from the number



step 5: goto step 3



If you didn't eventually get tired or bored you would be switching between the 2 results forever. Computers don't get tired or bored.






share|cite|improve this answer
















  • 2




    Good answer, but it leaves out an important word that appears in some of the others: That is, "state." Your answer illustrates the fact that even though a real computer can only have a finite number of possible states, nothing prevents it from cycling through some subset of those states, over and over again forever.
    – Solomon Slow
    Nov 11 '18 at 20:07







  • 1




    I'd propose to remove state altogether, as it's not mandatory.
    – phresnel
    Nov 12 '18 at 8:06


















29














In a contemporary processor there is, among many other things, a register (digital electronic component to hold some bits) called the Program Counter (PC). It holds the memory address to the current machine instruction.



During normal flow of the program, the PC will always be updated to address the next instruction. However, any loop will be implemented with so called branch or jump type instructions which will cause the PC to address some other instruction, rather than the next one.



One, if not the, simplest infinite loop, is one in which the PC is updated again to the same instruction.



An assembly (MIPS) code example (beq stands for Branch on Equal):



LABEL: beq $0, $0, LABEL # Comment: If 0 == 0,then goto LABEL.





share|cite|improve this answer






























    5














    At the most basic level, an "infinite loop" only requires two transistors — an astable multivibrator will alternate between two different digital states indefinitely as long as it has power. In some sense, every other loop is just a bigger version of this. You don't need more and more transistors to keep operating for a longer period of time.



    But what you might notice is that the astable multivibrator only has two states. Q is on, then Q is off, then Q is on again. It can only do two things before it repeats. There isn't really anywhere else for it to go. This is a general limitation: a system with a finite state can only go through a finite number of states before it repeats. The more transistors you have, the more "interesting stuff" you can do in your infinite loop. But with "only a couple billion" transistors there are trillions of possible combinations, which is quite a lot. And that's not even counting the RAM, which adds more billions (or even a trillion) more bits of state, making the number of possible states that the system can be in truly massive. As such, it's possible (even fairly easy) to write a program that, e.g. generates prime numbers, and keeps running for longer than the probable lifetime of the hardware (or even the solar system), without running out of different possible combinations of on/off transistors.






    share|cite|improve this answer




























      4














      You only need two transistors for that, as demonstrated by the old joke.



      How do you keep a (insert ethnicity here) busy forever?



      Write "Please turn over" on both sides of a sheet of paper.



      It's as true for transistors as for humans with a sheet of paper. In this case, two transistors make a bistable oscillator, and they'll toggle between true and false for as long as there's power there.






      share|cite|improve this answer






























        1














        One thing other answers have missed is that CPUs have a clock source, an external device (usually a quartz crystal oscillator) which switches from 0 to 1 and back a fixed number of times a second. This clock signal is what makes the CPU go from one instruction to the next. If the clock signal is too fast, the transistors that "perform" the instruction haven't finished charging up and so the results are garbled.



        Modern CPUs do very complicated things for performance reasons but this is the basic idea.



        Maybe that is enough to understand how the CPU moves from one thing to another thing and then moves back to the beginning. But I will go into a bit more detail.



        Inside the CPU are memory cells using a fixed number of transistors which can be overwritten with new values. There is also a fixed number of transistors that perform various computations, like addition, comparison, and so on. The clock opens the gate to allow data to "flow" from the memory cells, through the "compute" portion, and then the result is allowed back into the memory cells.



        So if your instructions are as follows:



        1. x = 5
        2. y = x + 1
        3. Go to step 1


        the processor will end up in exactly the same state when it starts each loop. (Well, in theory.)






        share|cite|improve this answer




















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          5 Answers
          5






          active

          oldest

          votes








          5 Answers
          5






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          25














          step 1: take a calculator



          step 2: input a number



          step 3: add 1 to the number



          step 4: subtract 1 from the number



          step 5: goto step 3



          If you didn't eventually get tired or bored you would be switching between the 2 results forever. Computers don't get tired or bored.






          share|cite|improve this answer
















          • 2




            Good answer, but it leaves out an important word that appears in some of the others: That is, "state." Your answer illustrates the fact that even though a real computer can only have a finite number of possible states, nothing prevents it from cycling through some subset of those states, over and over again forever.
            – Solomon Slow
            Nov 11 '18 at 20:07







          • 1




            I'd propose to remove state altogether, as it's not mandatory.
            – phresnel
            Nov 12 '18 at 8:06















          25














          step 1: take a calculator



          step 2: input a number



          step 3: add 1 to the number



          step 4: subtract 1 from the number



          step 5: goto step 3



          If you didn't eventually get tired or bored you would be switching between the 2 results forever. Computers don't get tired or bored.






          share|cite|improve this answer
















          • 2




            Good answer, but it leaves out an important word that appears in some of the others: That is, "state." Your answer illustrates the fact that even though a real computer can only have a finite number of possible states, nothing prevents it from cycling through some subset of those states, over and over again forever.
            – Solomon Slow
            Nov 11 '18 at 20:07







          • 1




            I'd propose to remove state altogether, as it's not mandatory.
            – phresnel
            Nov 12 '18 at 8:06













          25












          25








          25






          step 1: take a calculator



          step 2: input a number



          step 3: add 1 to the number



          step 4: subtract 1 from the number



          step 5: goto step 3



          If you didn't eventually get tired or bored you would be switching between the 2 results forever. Computers don't get tired or bored.






          share|cite|improve this answer












          step 1: take a calculator



          step 2: input a number



          step 3: add 1 to the number



          step 4: subtract 1 from the number



          step 5: goto step 3



          If you didn't eventually get tired or bored you would be switching between the 2 results forever. Computers don't get tired or bored.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Nov 9 '18 at 10:19









          ratchet freak

          2,57088




          2,57088







          • 2




            Good answer, but it leaves out an important word that appears in some of the others: That is, "state." Your answer illustrates the fact that even though a real computer can only have a finite number of possible states, nothing prevents it from cycling through some subset of those states, over and over again forever.
            – Solomon Slow
            Nov 11 '18 at 20:07







          • 1




            I'd propose to remove state altogether, as it's not mandatory.
            – phresnel
            Nov 12 '18 at 8:06












          • 2




            Good answer, but it leaves out an important word that appears in some of the others: That is, "state." Your answer illustrates the fact that even though a real computer can only have a finite number of possible states, nothing prevents it from cycling through some subset of those states, over and over again forever.
            – Solomon Slow
            Nov 11 '18 at 20:07







          • 1




            I'd propose to remove state altogether, as it's not mandatory.
            – phresnel
            Nov 12 '18 at 8:06







          2




          2




          Good answer, but it leaves out an important word that appears in some of the others: That is, "state." Your answer illustrates the fact that even though a real computer can only have a finite number of possible states, nothing prevents it from cycling through some subset of those states, over and over again forever.
          – Solomon Slow
          Nov 11 '18 at 20:07





          Good answer, but it leaves out an important word that appears in some of the others: That is, "state." Your answer illustrates the fact that even though a real computer can only have a finite number of possible states, nothing prevents it from cycling through some subset of those states, over and over again forever.
          – Solomon Slow
          Nov 11 '18 at 20:07





          1




          1




          I'd propose to remove state altogether, as it's not mandatory.
          – phresnel
          Nov 12 '18 at 8:06




          I'd propose to remove state altogether, as it's not mandatory.
          – phresnel
          Nov 12 '18 at 8:06











          29














          In a contemporary processor there is, among many other things, a register (digital electronic component to hold some bits) called the Program Counter (PC). It holds the memory address to the current machine instruction.



          During normal flow of the program, the PC will always be updated to address the next instruction. However, any loop will be implemented with so called branch or jump type instructions which will cause the PC to address some other instruction, rather than the next one.



          One, if not the, simplest infinite loop, is one in which the PC is updated again to the same instruction.



          An assembly (MIPS) code example (beq stands for Branch on Equal):



          LABEL: beq $0, $0, LABEL # Comment: If 0 == 0,then goto LABEL.





          share|cite|improve this answer



























            29














            In a contemporary processor there is, among many other things, a register (digital electronic component to hold some bits) called the Program Counter (PC). It holds the memory address to the current machine instruction.



            During normal flow of the program, the PC will always be updated to address the next instruction. However, any loop will be implemented with so called branch or jump type instructions which will cause the PC to address some other instruction, rather than the next one.



            One, if not the, simplest infinite loop, is one in which the PC is updated again to the same instruction.



            An assembly (MIPS) code example (beq stands for Branch on Equal):



            LABEL: beq $0, $0, LABEL # Comment: If 0 == 0,then goto LABEL.





            share|cite|improve this answer

























              29












              29








              29






              In a contemporary processor there is, among many other things, a register (digital electronic component to hold some bits) called the Program Counter (PC). It holds the memory address to the current machine instruction.



              During normal flow of the program, the PC will always be updated to address the next instruction. However, any loop will be implemented with so called branch or jump type instructions which will cause the PC to address some other instruction, rather than the next one.



              One, if not the, simplest infinite loop, is one in which the PC is updated again to the same instruction.



              An assembly (MIPS) code example (beq stands for Branch on Equal):



              LABEL: beq $0, $0, LABEL # Comment: If 0 == 0,then goto LABEL.





              share|cite|improve this answer














              In a contemporary processor there is, among many other things, a register (digital electronic component to hold some bits) called the Program Counter (PC). It holds the memory address to the current machine instruction.



              During normal flow of the program, the PC will always be updated to address the next instruction. However, any loop will be implemented with so called branch or jump type instructions which will cause the PC to address some other instruction, rather than the next one.



              One, if not the, simplest infinite loop, is one in which the PC is updated again to the same instruction.



              An assembly (MIPS) code example (beq stands for Branch on Equal):



              LABEL: beq $0, $0, LABEL # Comment: If 0 == 0,then goto LABEL.






              share|cite|improve this answer














              share|cite|improve this answer



              share|cite|improve this answer








              edited Nov 9 '18 at 22:57

























              answered Nov 9 '18 at 11:13









              Klorax

              52127




              52127





















                  5














                  At the most basic level, an "infinite loop" only requires two transistors — an astable multivibrator will alternate between two different digital states indefinitely as long as it has power. In some sense, every other loop is just a bigger version of this. You don't need more and more transistors to keep operating for a longer period of time.



                  But what you might notice is that the astable multivibrator only has two states. Q is on, then Q is off, then Q is on again. It can only do two things before it repeats. There isn't really anywhere else for it to go. This is a general limitation: a system with a finite state can only go through a finite number of states before it repeats. The more transistors you have, the more "interesting stuff" you can do in your infinite loop. But with "only a couple billion" transistors there are trillions of possible combinations, which is quite a lot. And that's not even counting the RAM, which adds more billions (or even a trillion) more bits of state, making the number of possible states that the system can be in truly massive. As such, it's possible (even fairly easy) to write a program that, e.g. generates prime numbers, and keeps running for longer than the probable lifetime of the hardware (or even the solar system), without running out of different possible combinations of on/off transistors.






                  share|cite|improve this answer

























                    5














                    At the most basic level, an "infinite loop" only requires two transistors — an astable multivibrator will alternate between two different digital states indefinitely as long as it has power. In some sense, every other loop is just a bigger version of this. You don't need more and more transistors to keep operating for a longer period of time.



                    But what you might notice is that the astable multivibrator only has two states. Q is on, then Q is off, then Q is on again. It can only do two things before it repeats. There isn't really anywhere else for it to go. This is a general limitation: a system with a finite state can only go through a finite number of states before it repeats. The more transistors you have, the more "interesting stuff" you can do in your infinite loop. But with "only a couple billion" transistors there are trillions of possible combinations, which is quite a lot. And that's not even counting the RAM, which adds more billions (or even a trillion) more bits of state, making the number of possible states that the system can be in truly massive. As such, it's possible (even fairly easy) to write a program that, e.g. generates prime numbers, and keeps running for longer than the probable lifetime of the hardware (or even the solar system), without running out of different possible combinations of on/off transistors.






                    share|cite|improve this answer























                      5












                      5








                      5






                      At the most basic level, an "infinite loop" only requires two transistors — an astable multivibrator will alternate between two different digital states indefinitely as long as it has power. In some sense, every other loop is just a bigger version of this. You don't need more and more transistors to keep operating for a longer period of time.



                      But what you might notice is that the astable multivibrator only has two states. Q is on, then Q is off, then Q is on again. It can only do two things before it repeats. There isn't really anywhere else for it to go. This is a general limitation: a system with a finite state can only go through a finite number of states before it repeats. The more transistors you have, the more "interesting stuff" you can do in your infinite loop. But with "only a couple billion" transistors there are trillions of possible combinations, which is quite a lot. And that's not even counting the RAM, which adds more billions (or even a trillion) more bits of state, making the number of possible states that the system can be in truly massive. As such, it's possible (even fairly easy) to write a program that, e.g. generates prime numbers, and keeps running for longer than the probable lifetime of the hardware (or even the solar system), without running out of different possible combinations of on/off transistors.






                      share|cite|improve this answer












                      At the most basic level, an "infinite loop" only requires two transistors — an astable multivibrator will alternate between two different digital states indefinitely as long as it has power. In some sense, every other loop is just a bigger version of this. You don't need more and more transistors to keep operating for a longer period of time.



                      But what you might notice is that the astable multivibrator only has two states. Q is on, then Q is off, then Q is on again. It can only do two things before it repeats. There isn't really anywhere else for it to go. This is a general limitation: a system with a finite state can only go through a finite number of states before it repeats. The more transistors you have, the more "interesting stuff" you can do in your infinite loop. But with "only a couple billion" transistors there are trillions of possible combinations, which is quite a lot. And that's not even counting the RAM, which adds more billions (or even a trillion) more bits of state, making the number of possible states that the system can be in truly massive. As such, it's possible (even fairly easy) to write a program that, e.g. generates prime numbers, and keeps running for longer than the probable lifetime of the hardware (or even the solar system), without running out of different possible combinations of on/off transistors.







                      share|cite|improve this answer












                      share|cite|improve this answer



                      share|cite|improve this answer










                      answered Nov 9 '18 at 17:26









                      hobbs

                      21315




                      21315





















                          4














                          You only need two transistors for that, as demonstrated by the old joke.



                          How do you keep a (insert ethnicity here) busy forever?



                          Write "Please turn over" on both sides of a sheet of paper.



                          It's as true for transistors as for humans with a sheet of paper. In this case, two transistors make a bistable oscillator, and they'll toggle between true and false for as long as there's power there.






                          share|cite|improve this answer



























                            4














                            You only need two transistors for that, as demonstrated by the old joke.



                            How do you keep a (insert ethnicity here) busy forever?



                            Write "Please turn over" on both sides of a sheet of paper.



                            It's as true for transistors as for humans with a sheet of paper. In this case, two transistors make a bistable oscillator, and they'll toggle between true and false for as long as there's power there.






                            share|cite|improve this answer

























                              4












                              4








                              4






                              You only need two transistors for that, as demonstrated by the old joke.



                              How do you keep a (insert ethnicity here) busy forever?



                              Write "Please turn over" on both sides of a sheet of paper.



                              It's as true for transistors as for humans with a sheet of paper. In this case, two transistors make a bistable oscillator, and they'll toggle between true and false for as long as there's power there.






                              share|cite|improve this answer














                              You only need two transistors for that, as demonstrated by the old joke.



                              How do you keep a (insert ethnicity here) busy forever?



                              Write "Please turn over" on both sides of a sheet of paper.



                              It's as true for transistors as for humans with a sheet of paper. In this case, two transistors make a bistable oscillator, and they'll toggle between true and false for as long as there's power there.







                              share|cite|improve this answer














                              share|cite|improve this answer



                              share|cite|improve this answer








                              edited Nov 12 '18 at 13:44

























                              answered Nov 9 '18 at 23:32









                              Graham

                              20912




                              20912





















                                  1














                                  One thing other answers have missed is that CPUs have a clock source, an external device (usually a quartz crystal oscillator) which switches from 0 to 1 and back a fixed number of times a second. This clock signal is what makes the CPU go from one instruction to the next. If the clock signal is too fast, the transistors that "perform" the instruction haven't finished charging up and so the results are garbled.



                                  Modern CPUs do very complicated things for performance reasons but this is the basic idea.



                                  Maybe that is enough to understand how the CPU moves from one thing to another thing and then moves back to the beginning. But I will go into a bit more detail.



                                  Inside the CPU are memory cells using a fixed number of transistors which can be overwritten with new values. There is also a fixed number of transistors that perform various computations, like addition, comparison, and so on. The clock opens the gate to allow data to "flow" from the memory cells, through the "compute" portion, and then the result is allowed back into the memory cells.



                                  So if your instructions are as follows:



                                  1. x = 5
                                  2. y = x + 1
                                  3. Go to step 1


                                  the processor will end up in exactly the same state when it starts each loop. (Well, in theory.)






                                  share|cite|improve this answer

























                                    1














                                    One thing other answers have missed is that CPUs have a clock source, an external device (usually a quartz crystal oscillator) which switches from 0 to 1 and back a fixed number of times a second. This clock signal is what makes the CPU go from one instruction to the next. If the clock signal is too fast, the transistors that "perform" the instruction haven't finished charging up and so the results are garbled.



                                    Modern CPUs do very complicated things for performance reasons but this is the basic idea.



                                    Maybe that is enough to understand how the CPU moves from one thing to another thing and then moves back to the beginning. But I will go into a bit more detail.



                                    Inside the CPU are memory cells using a fixed number of transistors which can be overwritten with new values. There is also a fixed number of transistors that perform various computations, like addition, comparison, and so on. The clock opens the gate to allow data to "flow" from the memory cells, through the "compute" portion, and then the result is allowed back into the memory cells.



                                    So if your instructions are as follows:



                                    1. x = 5
                                    2. y = x + 1
                                    3. Go to step 1


                                    the processor will end up in exactly the same state when it starts each loop. (Well, in theory.)






                                    share|cite|improve this answer























                                      1












                                      1








                                      1






                                      One thing other answers have missed is that CPUs have a clock source, an external device (usually a quartz crystal oscillator) which switches from 0 to 1 and back a fixed number of times a second. This clock signal is what makes the CPU go from one instruction to the next. If the clock signal is too fast, the transistors that "perform" the instruction haven't finished charging up and so the results are garbled.



                                      Modern CPUs do very complicated things for performance reasons but this is the basic idea.



                                      Maybe that is enough to understand how the CPU moves from one thing to another thing and then moves back to the beginning. But I will go into a bit more detail.



                                      Inside the CPU are memory cells using a fixed number of transistors which can be overwritten with new values. There is also a fixed number of transistors that perform various computations, like addition, comparison, and so on. The clock opens the gate to allow data to "flow" from the memory cells, through the "compute" portion, and then the result is allowed back into the memory cells.



                                      So if your instructions are as follows:



                                      1. x = 5
                                      2. y = x + 1
                                      3. Go to step 1


                                      the processor will end up in exactly the same state when it starts each loop. (Well, in theory.)






                                      share|cite|improve this answer












                                      One thing other answers have missed is that CPUs have a clock source, an external device (usually a quartz crystal oscillator) which switches from 0 to 1 and back a fixed number of times a second. This clock signal is what makes the CPU go from one instruction to the next. If the clock signal is too fast, the transistors that "perform" the instruction haven't finished charging up and so the results are garbled.



                                      Modern CPUs do very complicated things for performance reasons but this is the basic idea.



                                      Maybe that is enough to understand how the CPU moves from one thing to another thing and then moves back to the beginning. But I will go into a bit more detail.



                                      Inside the CPU are memory cells using a fixed number of transistors which can be overwritten with new values. There is also a fixed number of transistors that perform various computations, like addition, comparison, and so on. The clock opens the gate to allow data to "flow" from the memory cells, through the "compute" portion, and then the result is allowed back into the memory cells.



                                      So if your instructions are as follows:



                                      1. x = 5
                                      2. y = x + 1
                                      3. Go to step 1


                                      the processor will end up in exactly the same state when it starts each loop. (Well, in theory.)







                                      share|cite|improve this answer












                                      share|cite|improve this answer



                                      share|cite|improve this answer










                                      answered Nov 9 '18 at 23:10









                                      Artelius

                                      30112




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