echoSwe said:
But is it THE limiting factor?
It might be for some designs, but not for others. There are a variety of limitations, and any of them can be the dominant limiting factor for any given design.
Processors are built on silicon wafers, slices of pure crystalline silicon, which naturally have some amount of impurities scattered throughout them. A large transistor, which uses a large area of the wafer, would not be much affected by a very small spot of impurity. A very small transistor, however, could be totally ruined by it.
No you can't. You can't just make a big CPU... Explain yourself.
Of course you can make a very large, very high clock frequency monolithic processor -- that's the approach Intel's been taking for decades. An alternative approach is to build distributed computers, with lots of independent processors working in parallel. This is the approach of companies like Sun, IBM, and SGI.
I don't believe I ever implied that HyperThreading (which is nothing more than two CPU state machines sharing one CPU's worth of functional units) is anything like a distrbuted supercomputer. That was, after all, my point: there are two approaches currenly in vogue, monolithic and distributed.
Are you saying my own computer works like this?
No. Your personal computer is probably based on a single monolithic processor by Intel or AMD.
What I meant is this: even if you have amazing cooling systems that can remove heat at a ridiculous rate from the surface of a chip's package, that cooling system is worthless if the heat from the die itself can't make it out of the package efficiently enough.
1) But isn't the limit reached now, when they can't make the transistors any smaller? Because if they do it leads to, what dduardo said, electrons tunneling through the polysilicon gate into the body of the tranistor?
Process geometries continue to shrink. The limit has not been reached yet, but it is looming in the near future.
Btw - what is the gate in a transistor? Is it where the electric signal exits the transistor?
As has been explained already, the gate of a field-effect transistor is the electrode which is used to selectively deplete the transistor's channel, changing its conductivity.
3) Do you have any tips on where to find more information about this?
Get a college textbook on microarchitecture.
4) And this is what will come?
Distributed computing is already the norm in scientific and numerical computation. It does not benefit the desktop user much, because desktop tasks do not lend well to parallelization.
What's the difference between semi conductors and transistors? The whole, not the "basically" difference?
You're asking questions that really require several years of education to "wholly" answer, so you're going to have to deal with some basic answers.
Semiconductors are materials which can act as either insulators or conductors, depending upon the electric fields applied to them. Raw, natural silicon is an insulator. You can dope the silicon with impurities like phoshorus and boron, which result in materials with an excess or scarcity of electrons. Placing these materials together results in junctions across which electrons can flow one direction but not the other. These junctions are called diodes. You can slap two such diodes together and build a basic transistor. You can build complex devices by wiring many such transistors together. Field-effect transistors operate on a different principle, but still involve the same physical principles.
So,
basically, semiconductor is the bulk, raw material out of which transistors are made. If you want more detail, you'll either have to ask more specific questions, or consult a semiconductor device physics textbook (I suggest Neaman), or pursue a graduate education in electrical engineering. I cannot explain it all to you on a forum.
Because the impedance of a capacitor is frequency dependent. The displacement current is proportional to the rate of change of the electric field. The faster the field changes, the more displacement current you see, and the lower impedance the capacitor appears to have.
Interessting. So there is a limit to how small you can make the walls of the transistor? Has this got anything to do with quantum mechanics?
There isn't a specific hard limit like a brick wall. Instead, the limit is a fuzzy area where it becomes increasingly difficult (and decreasingly economical) to make smaller structures. It does indeed have to do with quantum mechanics. Electrons have characteristic wavefunctions which are not localized. If the size of your barriers is comparable to the size of the wavefunction of the electron, the electon can spontaneously appear on the other side of supposedly impenetrable barriers. You essentially cannot trap electrons in very small spaces. Much research is being done on the behavior of electrons in "low-dimensional" spaces, like quantum dots.
I've heard some approximations about when the limit for our technology will be reached, and they were 4, 5 and 10 GHz.
Try not to think of a processor's speed in terms of its master clock cycle; that's very deceptive. Novel processor architectures, compiler architectures, heat rejection systems, packaging, and more all contribute to the computational power of a computer.
Now, I know this is approximations, so don't comment on these numbers, because they just give you a feel for it (...). What more can be done to increase the clock speed now? Since raised voltage can increase the frequency, will they do that, and start shipping the CPUs with water cooling, and in the end liquid nitrogen or something like this?
That's one approach, but it's not very practical. There are better ways to build faster computers, as we've already explained.
(And if they ship it with liquid nitrogen - doesn't the electrons freeze/the current stop?)
Electrons do not freeze. On the grand scheme of things, liquid nitrogen is really not very cold.
What makes could make the development come to a stop, at these frequences?
The same limitations we've been discussing all along.
If you consider the spin of electrons - can you do anything from that?
Yes, spintronics is a new and very promising technology that uses the spin states of electrons to encode information.
- Warren
