How does a COMPUTER CPU actually WORK?

this video is sponsored by onedreams stay tuned to the end to find out more think of any computing device or computer activity you take for granted shopping on your smartphone playing games on your computer watching this video on a notebook all these devices and activities are made possible by something that is not that dissimilar from this light switch a standard light switch simply turns a light either on or off yes or no true or false that's it remarkably the brain of your computer called the cpu or central processing unit is made up of essentially billions of light switch-like components called transistors a transistor is simply a device that either has a current flow through it or not when a current is flowing it is odd or true or equivalent to a one when no current is flowing it is off or false or equivalent to a zero this is what binary means a one or zero a standard computer at its essence only understands this binary language what is a 1 and what is a 0 that's all so the question is how does a simple device like a transistor result in the myriad of complexity and sophisticated devices capable of enabling so much of our modern lifestyle and essential activities to answer this question i want to take you on a journey inside the cpu of a computer and show you how it actually works in addition i'll point out the essential differences in how a cpu of a quantum computer would work versus a classical computer cpu you don't want to miss what's coming up right now let's do a quick review of the main components of a computer for any computer to work it needs a power supply because energy is needed to run the system a computer works with a lot of data so it needs a place to store the data for storage of bulk data hard drives and solid state drives are used but bulk storage devices are simply too slow for the speeds needed to transfer data with the processor to help this issue most computers have something called ram or random access memory which is much faster than any hard disk or ssd and it's also physically closer to the processor allowing higher bandwidth and faster flow of data all these devices are really ancillary to the main component of the computer which is the central processing unit or cpu this is the brain of the computer that does the actual computation the device that you're likely watching this video on like a laptop notepad phone etc contains such a processing unit a classical cpu is made from transistors a transistor is basically like an on off switch if it is on then it's like the number one and if it's off it's like the number zero groups of transistors connected in the appropriate way form what's called logic gates these logic gates do the actual computation in cpus to understand how logic gates work let's look more closely inside a cpu we'll do this by looking at the very first commercially available general purpose processor which was introduced by intel corporation in 1971 called the intel 4004 by looking at this relatively simple processor we will get an idea of the architecture of the cpu the 4004 was a four bit processor this means it can work with inputs formed by four bits and again one bit is nothing but either one or zero thus the processor could accept an input like one zero one one this is also called a word a word is an object made from ones and zeros with which the cpu works and in the case of the intel 4004 it was four 4-bit words it consists of 2 250 transistors to give you an idea of how much we have progressed in 50 years modern processors are 64-bit processors and consists of billions of transistors now let's look closer at how a computer actually works by processing just ones and zeros the internal diagram of the intel 4004 chip looks like this there are some timing controls at the bottom responsible for keeping the operation synchronized because if not synchronized the computer will get lost with what it's trying to do and crash we have some registers and an address stack for storing values to keep track of the data we're working with there's also an instruction decoder that helps decipher the code and figure out what the cpu should be processing and we have some io or input output to communicate with other components of the computer the magic all happens at this red thing called the alu or arithmetic logic unit this is where everything is calculated in process the rest is mostly just data management and data storage so it's really not that complicated basically you take some input perform a set of operations on it and then you get an output the end result is a set of output data now there are many more components needed to make all this synchronized and smooth but essentially that's it how it's processed at the alu is determined by the instructions that it is given in modern cpus there can be many such alus as part of so-called executive units and then each of these units can specialize in different tasks like addition or multiplication let's do a quick example to see how an alu works let's say we want to add two numbers two and three these two numbers will be represented by four binary bits in binary code two is represented as 0 0 1 0 and 3 is represented as 0 0 1 1. these are the input bits also called operands to add them together the instruction code must tell the alu to add them this will be specified by some flag that tells it what to do with the operands it receives these are sent to the alu in the form of a set of binary bits so for example the flag could be 0 0 and this could mean add and 0 1 could mean multiply and 1 0 could be subtract and 1 1 would mean division some of the bits of the original instruction code will be flags and some will be the inputs we need to add multiply subtract or do some other operation how exactly all this works is different for different types of cpus then the alu processes these inputs and outputs a result now in order to compute the results a lot of complex logic is needed the logic is built into the processor using something called logic gate now what is a logic it's actually rather simple there are different variants but essentially a logic gate takes in two bits thus two binary numbers of a single digit then depending on the type of logic gate it is and depending on what value the bits have the gate will output a result bit physically these gates are made from a bunch of transistors connected in the appropriate way for whatever gate you want to make a simple example would be the and gate in the and gate if the two incoming bits are one thus true then the output is one otherwise the output is false or zero this is easier to understand in terms of truth tables where 1 is true and 0 is false another gate is the or gate here if either or both of the incoming two bits are one then the output is one otherwise the output is zero now what if we only want the case where the gate is true if and only if one input is one and the other is zero otherwise it is false this is called an xor or xor gate there are several more gates but you get the idea with the and or or xor gate we can construct a circuit which can add numbers but before we get to that let's look at how a logic gate is built using transistors after all the transistor is the core building block of a cpu the add gate is rather simple to build you just need two transistors and some appropriate resistors there are different ways to physically construct a logic gate so this is just one example the and gate takes in two inputs and if those two inputs are true or one then the output is on or one or true so let us take one transistor and attach some power source to it thus the source input is a then we connect the first input a as the gate input to the transistor thus if the input a is on or connected then the gate will have electricity flowing through now the second transistor has to also be on for the output to be one if either a or b are not connected in other words if either is zero then the output will be zero they both have to be one for the output to be one this is exactly how an and gate should work we can also make an or gate with two transistors if we just change the wiring a bit in this case if either a or b transistors are on the output will be one it will be zero only if both transistors are off the xor gate is a little bit more complicated but the idea is the same it's just a couple of transistors and resistors to regulate the signal and then everything must be wired in the correct way how can we then use these logic gates to add numbers for this we need two xor gates two and gates and one or gate this is called a full adder circuit here a and b is the input to add and c n is the carry bit from the c out output this is needed to carry over bits for example in elementary school when you learned to add five plus five then you had to carry the one for the tens unit and put a zero in the one spot it works the same way in binary language the carry out bit is the same concept this might seem trivial but a computer is fundamentally just doing first grade math really fast of course computers work with binary numbers so in the cpu we would get a carry if we add one and one since anything larger than a one would require a carry in binary let's now add two numbers two and three first we must convert them into binary using four bit numbers we can write 2 in binary as 0 0 1 0 and 3 as 0 0 1 1. from right to left we have 0 and 1 through the xor gate the result is 1 or true in the beginning of the calculation the c n starts with a zero since there's no carry from the c out when the zero from the c in is combined with the one from the first xor gate into the second xor gate we get a one for the output now if we continue with the first and gate the inputs will be 0 and 1. the result will be 0. the input for the second and gate will be 0 and 1 from a and b the result will be 0. 0 and 0 through the or gate will also result in a zero next we again have one and one for the input and the result is zero because the previous c out was zero then c n will be zero again if we continue we will see that we have a zero at the second xor gate and the first and gate but this time since both a and b are one then the second and gate will return a one now since we have zero and one as the input for the or gate the result will be a one we get that the c out is one we thus have a carry to consider in the next step for a and b this time we have zero and zero which is zero from the first xor connected to a and b but now we have a carry so cn is now 1. this means that in the second xor gate we now have 0 and 1 as the input so we get a 1 as the result now as a and b is 0 there is no carry out so c out is now 0. in the last step we have zero and zero as the input and since the c in is also zero then everything is zero and the result of this round is zero all around if we collect all the results from our four rounds of computation then we get that zero zero one zero plus zero zero one one equals zero one zero one and if we convert this into standard integer numbers we get five so voila two plus three is equal to five and this is exactly what we would expect from this adder logic circuit similarly logic gates can be constructed to do other things so in this way a computer can do all kinds of cool things but it's easy to forget that these logic circuits are just doing first grade math the circuitry and architecture of the computer as a whole is complex but it is built around an elementary concept this is roughly how a classical processor works you have some timing management components and a lot of storage for instructions and the data which the processor needs to work the alu then executes and performs the actual calculation to give you some result that's it now how do quantum computers differ quantum computers in principle do the same computations as a classical computer but there are a couple of differences instead of bits the quantum processor uses qubits to do the computations qubits are bits that are in a superposition of both zero and one but they can potentially take on an infinite number of values between zero and one they could be made with one of many quantum objects like electrons or photons that have some binary property like spent stupids being in superposition have some significant advantages if you want to learn more about why this is so powerful check out my prior video about quantum computers because qubits can be in a state of both 0 and 1 at the same time qubits can store 2 to the power of the equivalent number of bits so three qubits can hold the same amount of data as two to the third or eight classical bits and just 10 qubits would be able to store the same data as 2 to the 10 or 1024 classical bits now qubits are quite different physically compared to the bits of a classical computer in the classical computer we use electrical signals that flow through a circuit if there's a signal you have a one state if there's no signal you have a zero state the qubit on the other hand is usually stationary it's located in a physical place on the quantum chip so they do not flow like classical bits through a gate the gate has to be applied onto the stationary qubits this can be done using photons in particular using microwave pulses but the exact detail depends on the design of a specific chip we're still in the early days of quantum computing so many different approaches are being tested instead of classical logic gates quantum computers use quantum logic gates in the quantum case we can also make a full adder to add two numbers but instead of and gates we use what's called to foley gates and instead of or or xor gates we use c not gates at face value the quantum full adder isn't really anything special the gates are slightly different but we're still just doing simple operations the magic of the quantum computer comes from the fact that the quantum logic gates can work with cubits we have two qubits in this circuit so instead of adding just two numbers together we could potentially do four additions at the same time if we had three qubits we could do eight additions at once and so on adding two numbers on a quantum computer isn't any better than on a classical computer but something like finding a specific number among billions of numbers like a reverse phone number search is relatively easy for example let's consider that we want to find a phone number where for simplicity the number is between zero and eight this is the biggest number that we can write with three classical bits the classical computer would then just start from one end and ask is this the right number so first it would try 0 0 0 then 0 0 1 then 0 1 0 then 0 1 1 and so on on a quantum computer we can take 3 qubits and make a superposition of all eight possible numbers and thus search the entire space of possibilities in just one search instead of up to eight one thing that quantum computer scientists agree on is that it won't solve every type of problem it's well suited only for certain kinds of challenges like probability problems optimization like finding the best possible travel route or a needle in a haystack type of problems the challenges that quantum computing faces isn't in the hardware but the real magic of the quantum computer comes from the algorithms used to solve these problems using qubits not better machinery or speed as new algorithms are developed we'll find more ways to use quantum computers in more applications the past might be classical but the future is almost certainly going to be quantum if you want to learn more about computers and quantum mechanics then consider subscribing to wondering today's sponsor one of the courses that helped inform me during the research for this video is called the science of information from language to black holes it's taught by one of my favorite educators benjamin schumacher of kenyan college this is a 24 lecture series which teaches you everything from logic gates to cryptography to cubits to the connection between reality and information you can not only enjoy these great lectures by professor schumacher but also some of the best educators in the world you'll be hard-pressed to find a better online learning service than one dream i myself have been a member for a very long time i can't recommend them enough you'll even see my testimonial at the bottom of one dream's homepage it's really easy to sign up right now because they are offering a free trial and you can cancel at any time but there's really nothing to lose if you want to support this channel and greatly increase the depth of your knowledge be sure to click the special link in the description and if you have a question or comments from me please leave them in the comment section because i try to respond to all of them i'll see you in the next video my friend [Music] you

Channel: Arvin Ash

Views: 180,599

Keywords: how do computers work, classical computing vs quantum computing, difference between classical and quantum computing, classical computer vs quantum computer, central processing unit, central processing unit in computer architecture, arithmetic logic unit, how does a cpu work, intel 4004 architecture, what are logic gates, how do logic gates work, transistor circuit for or gate, transistor circuit for and gate, how does quantum computer work, quantum computing, quantum computer

Id: EsDyGfh8bnM

Length: 18min 29sec (1109 seconds)

Published: Sun Sep 19 2021