My knowledge is very vague as all we have are visual diagrams etc, but we have memory address and registers, the ALU being the heart(apparently). Single core CPUs process one instruction at a time AFAIK and multi-core have parallelism to some degree. So where do the millions of transistors come in and how do 32 registers manage everything. We have FPU's I know, how many transistors would these use roughly. Any way to get a fairly simple idea of what the bulk of the transistors do, why more means faster and how the registers 'manage' everything.

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    $\begingroup$ I think this is below the resolution of CS; maybe this question would be better off on Electrical Engineering? (This question may be helpful.) $\endgroup$
    – Raphael
    Feb 7, 2014 at 7:50
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    $\begingroup$ Why do you say that the registers manage the CPU? That seems like saying that a piece of paper on my desk manages me; isn't it the other way around? $\endgroup$ Feb 7, 2014 at 10:43
  • $\begingroup$ fairly similar to this question how does a computer work. the question seems to be about how the different transistors are allocated across different fns of the cpu. actually ALU mentioned takes a significant part... as for last question "how the registers 'manage' everything" is not very meaningful, registers do not "manage" anything, its more eg that a compiler "manages" the use of registers through optimization etc.... one can write working code that uses almost no registers. $\endgroup$
    – vzn
    Feb 7, 2014 at 16:07
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    $\begingroup$ Why does more transistors = more processing power? on the Electrical Engineering SE might be of interest. (I am somewhat proud of my answer there, but it might be a little too technical.) $\endgroup$
    – user4577
    Feb 7, 2014 at 16:24

4 Answers 4


This is a huge question. To fully answer it would take far more space than you'd want to read (not to mention that I suspect that there's a limit on the length of any SE answer), but I'll try to give you an idea of what goes on in the CPU.

First, a transistor (when used in a CPU) is essentially a switch, like a light switch except that you don't have to turn it on or off manually. Rather, it is controlled by an electrical current. The most important thing to understand is that modern computers are two-state devices: the only thing that really matters is whether a wire has a current or not.

One then begins the process of chip design by, for example, deciding how an integer (or other data) will be represented. For integers, say, the chip designers generally decide to them by ganging wires together in a logical unit, so with a collection of four wires it would be possible to represent 16 possible patterns: $\mathtt{0000}, \mathtt{0001}, \dots \mathtt{1111}$, where a pattern like $\mathtt{1101}$ would represent a voltage in wires 1, 2, and 4, and no voltage in wire 3 and this collection might be interpreted as the number 13. In this example, we'd have what's known a a 4-bit chip. A modern computer would have either 32 or 64 wires treated as a unit.

It happens that with a suitably-connected collection of switches (aka transistors), one can do things like add two numbers, compare two numbers for equality, decide whether a number is zero or not, and so on. Often, all of these operations are often done at once, simultaneously, and the relevant one is chosen by the current instruction, which determines which of the various results to use, and where that result will be sent. All of this traffic control is also controlled by switches, depending on what the current instruction is (in the program being executed). In addition, things like memory and registers which store information can also be implemented by these switches.

To get a feel for the number of transistors used, an adder circuit in a $n$-bit computer might require about, say, $20n$ transistors, an $n$-bit register might require $50n$ transistors, and the traffic control circuitry to sent the results to the right place might require several hundred more for each bit. It's not hard to imagine that with a lot of functionality and a wide data path (the number of wires ganged together) a modern CPU could easily take millions of transistors.

As to why "more [transistors] means faster", the answer is "not necessarily", but in general, doubling the width of the data path, say from 32 bits to 64, gives you the ability to manipulate larger numbers in a single instruction at the cost of requiring more transistors.

Finally, the registers don't really "manage everything". A register is simply a very fast storage unit, capable of storing and retrieving information far faster than, say RAM memory. For that reason, things like the current instruction are often stored in a special register (called the instruction register), simply because access to its bits is very fast. The current instruction actually "manages everything", and it's stored in a register for speed.

This is a very abbreviated explanation---I've left out a ton of detail and glossed over a lot of technical matters, but I hope it at least gives you a sense of what goes on in a modern computer. [entering duck-and-cover mode in expectation of howls of complaints from computer engineers]

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    $\begingroup$ The 'more means faster' came from the many years when Moore's Law (transistor scaling) and frequency scaling were happening at almost the same rate. In many people's minds they're still conflated a bit. One other thing to mention- there's an impression here that everything is linear; however, there's a number of places where the number of transistors will be polynomial or higher in the number of stages, or elements, or wires. $\endgroup$
    – Matthew G.
    Feb 7, 2014 at 14:33
  • $\begingroup$ This is a great short answer. If you want the long and detailed answer from an extremely gifted author and famous early Windows programming guru, I recommend the book, Code, by Charles Petzold. I've given away 7 or 8 copies of this book, and I recommend it to anyone who wants to know how modern computers work. He begins with simple logic building blocks that can be build from electrical relays and follows progression all the way to a simple CPU with memory access. With each developing chapter you see where all the transistors go. His book web page: charlespetzold.com/code $\endgroup$
    – inflector
    Jan 31, 2016 at 21:11
  • $\begingroup$ Still cannot account for the billions of transistors required. I don't think the number of registers or the data path has changed over the many generations of the i7 CPU. Unless, say, duplicating a core requires something like 500 million transistors. $\endgroup$
    – Old Geezer
    Jul 23, 2022 at 1:52

Typically one bit of cache memory requires 6 transistors (some designs use more or less, with different tradeoffs; see http://en.wikipedia.org/wiki/Static_random-access_memory), so modern CPUs with large caches spend a lot of transistors there.

Modern CPUs also execute multiple instructions concurrently, so there are multiple execution units (ALUs) on the chip, each of which is fairly complex.

Certain mathematical algorithms in the FPU can be accelerated by table lookup plus interpolation; the reciprocal square root instruction in Intel SSE units, for example, is implemented with a table that gives 12-bit precision almost instantly; this table is essentially a chunk of ROM on the chip -- that is, still more transistors.


there are several questions here & will just focus on one of them. the transistors on a chip is "roughly" proportional to the surface area used for the transistors. so you can find diagrams of a chip that show the graphical boundaries of different subsystems and simply use the formula that # of transistors in a region is equal to the proportion of area of that region to total area times total number of transistors on the chip.

example in this paper:

fig 1 shows the graphical boundaries on the chip. see fig 4 that gives area and # of devices in the millions for the separate functions of the CPU. the exception is that it appears that cache circuits are very dense and have much more transistors per area, it seems to have 3x the transistors at 2/3 the area. apparently on this chip it looks like about ¾ the transistors are dedicated to fast cache.


The simple answer is transistors are the basic components of logic gates, registers and storage devices. their various configurations make possible the or and not and flip-flops that comprise the higher order registers and processors. Look up the 7404 (not gate)7408 (and) and the 7432 (or gates). the basic 7474 and the 74279 are storage configurations. I am not sure if national semiconductor still publishes the actual schematic but texas instruments does.

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    $\begingroup$ You are digging up lots of old questions, posting answers that don't seem to be adding much (or in a very convincing form). Before answering, please consider carefully if you can truly add something that prior answers fail to provide, and take care to present it in a digestible form, adhering to scientific standards (references, proofs, ...) $\endgroup$
    – Raphael
    Jul 21, 2015 at 19:58
  • $\begingroup$ I did not see any actual circuitry answers to the questions. I think clarity and simplicity add to the discussion. not really interested in your opinion of my contributions or rating of my answers. in fact I find your response rather snobbish and condescending. maybe you should adhere to the same expectations and stop trying to control others right to free speech. $\endgroup$
    – SkipBerne
    Jul 21, 2015 at 20:26
  • $\begingroup$ 1) As a moderator, I'm warning you to adhere to our standards in order to help you avoid disappointment. 2) I don't care about your opinion of my statements. 3) Free speech does not apply here. This is a website owned by a company, with a community given mandate to moderate. $\endgroup$
    – Raphael
    Jul 22, 2015 at 6:03
  • $\begingroup$ using this case in point I did present references, in fact I cited the BIBLE of TTL logic written by TI. I thought that the individual posting this question was unclear about logic electronics and need some on to point them to the basics. what about this does not add to the discussion? $\endgroup$
    – SkipBerne
    Jul 22, 2015 at 15:45
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    $\begingroup$ For one thing, I don't see any reference that can be recognized as such in your post. Then, you only seem to say "they are the basic building blocks of logic gates, which CPUs are build of". Other answers already say the same in a much more elaborate and explanatory way. $\endgroup$
    – Raphael
    Jul 23, 2015 at 7:02

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