# Physical limitations of computer speed

• jhirlo
In summary, Taylor and Wheeler explore the problems with data communication and how we are trying to overcome physical limitations. They state that the speed of light is a limitation, but for data communication, since fiber optics has not yet been used as a technology for computer busses and CPU data paths. The constant c however, in the context of data communications, brings propagation delays which are ignorable. The important thing is the bandwidth (data rate) carried by light.
jhirlo
We can agree that there are limitations originating from physical principles (constanats) computer speed.
On many sites I read common sentence was one referring to CPU frequency increment. It’s sad that as we increase CPU’s working frequency we have to locate memory (RAM) closer to CPU because this length has to be smaller than the wave length of given frequency, why ?
Than there’s the problem with constant for speed of light….

What are your thoughts on this subject, how do you think we’ll try to pass this barriers?

jhirlo said:
We can agree that there are limitations originating from physical principles (constanats) computer speed.
On many sites I read common sentence was one referring to CPU frequency increment. It’s sad that as we increase CPU’s working frequency we have to locate memory (RAM) closer to CPU because this length has to be smaller than the wave length of given frequency, why ?
Than there’s the problem with constant for speed of light….

What are your thoughts on this subject, how do you think we’ll try to pass this barriers?

Taylor and Wheeler (1992) explore this problem in one of the exercises in
Spacetime Physics. In their book, Taylor and Wheeler assume that each instruction involves the transmission of data from the memory to the processor where the computation is carried out, followed by transmission of the result back to the memory. If the average distance between the processor and the memory is $\ell$, then distance covered by the signal during one instruction is $2\ell$. Assuming the signal propagates at the maximum possible celerity $c$, then the time taken to carry out one instruction is $2\ell/c$. Today's computers are capable of performing billions of instructions per second. A one gigaflop computer may carry out up to 1 billion sequential instructions per second. So the duration of each instruction is $2\ell/c = 10^{-9}s$. This allows us to calculate the value of $\ell$. It can be seen from the equation that if the time for one instruction decreases, then the value of $\ell$ must decrease to keep the equation balanced.

jhirlo said:
Than there’s the problem with constant for speed of light….
The speed of light is a limitation, but for data communication, since fiber optics has not yet been used as a technology for computer busses and CPU data paths. The constant c however, in the context of data communications, brings propagation delays which are ignorable. The important thing is the bandwidth (data rate) carried by light.
Physical limits on the bandwidth of electical data communications are implied by Nyquists' theorem (on the rate that hardware can change signals) and by Shannon's law (on the effects of noise on data rate).

We may not use fiber optics, but the signals on an integrated circuit still travel at a speed slower than 'c'.

The wiring traces on an IC can be modeled as a lossy transmission line. (The substrate serves as a ground plane, and the glass insulation serves as the dielectric). The speed of propagation of electical signals along this transmission line is (of course) less than 'c'.

Note though that not all memory accesses have to occur at the operating speed of the processor, because of a technique known as "cache". The most commonly used memory locations are kept close to the CPU in very fast memory. Usually some portion of the CPU is dedicated to cache memory nowadays (level 1 cahce). There's also often some external cache as well (level 2).

Parallel processing is another way around the speed-of-light limit, as are other tricks such as out-of-order execution. A lot of these tricks are already being used, the typical marketing specification of a prcoessor's "speed" has only a vague resemblence to the actual clock rate of the CPU.

We haven't even cme close to meeting the basic physicaly limitations of computers. Like networking, for instance, physically those cat5 cables ca carr way more than they do. However, we just have trouble making the parts that pus them to the limits, so to speak.

We're starting to getting close to the limits of standard silicon, even if we aren't close to the theoretical limits of computation. Of course you may not consider 20 years more of growth at the current rate "close", depending on your viewpoint. The 20 year figure comes from

article

Does Nyquist's Theorem regarding rate of signal change also imply limitations to the speed of microprocessors? Does it have any relationship with the limitation of constant c?

## 1. What is the maximum speed that a computer can operate at?

The maximum speed at which a computer can operate is dependent on various factors such as processor speed, memory capacity, and storage speed. However, the theoretical limit for the speed of computers is determined by the speed of light, which is approximately 299,792,458 meters per second.

## 2. Can computer speed continue to increase indefinitely?

No, computer speed cannot continue to increase indefinitely. As technology advances, the physical limitations of computer components, such as the size of transistors and the speed of electrons, become more apparent. There will eventually be a limit to how fast computers can operate.

## 3. How do physical limitations affect the performance of computers?

Physical limitations, such as the size and speed of components, can affect the performance of computers by limiting their processing speed and memory capacity. This can result in slower operations and longer loading times for complex tasks.

## 4. Are there any potential solutions to overcome physical limitations of computer speed?

Scientists and engineers are constantly working on new technologies and techniques to overcome physical limitations and improve computer speed. Some solutions include using new materials for components, developing new architectures, and utilizing parallel processing.

## 5. How do physical limitations of computer speed impact the development of new technologies?

The physical limitations of computer speed can impact the development of new technologies by limiting the capabilities and performance of these technologies. For example, artificial intelligence and virtual reality require high-speed processing, and if computers are not able to keep up with the demand, it can hinder the advancement of these technologies.

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