The challenge of the future
Microprocessors are a breakthrough in computer technology. A whole computer in a small silicon chip! Microprocessors have expanded the range of computer use to the personal level. Microprocessors are at the root of everything from personal computers, laptops to smartphones, tablets. The microprocessor that started the journey with the Intel 4004 chip in the seventies, a few decades later today the microprocessor is much more efficient and powerful. In the last 20 years, the performance of this chip has increased almost a thousand times. This is due to the continuous improvement of transistor technology and processor design. Over time the speed of transistors and the density of silicon chips have increased, with new features added to the processor design. Combining these two, the performance of the microprocessor has been steadily increasing. But the rate of increase in the speed of the transistor is decreasing than before. At the same time increasing the power consumption of the transistor, Which is limiting the speed of the microprocessor. Currently the main challenge of microprocessor design is how to get maximum performance on a limited power budget.
Microprocessor speeds have made remarkable progress over the past few decades, following Moore’s Law. At the heart of Moore’s formula is the scaling of transistor technology. For every new transistor technology generation (every two years), The dimensions of the transistor can be reduced by 30 percent. Due to this the size is reduced by 50 percent. With it the speed of the transistor increases by 40 percent. And the amount of electricity consumption is reduced by 50 percent. Many new and complex micro-architecture features have been added to the microprocessor design using this new generation of additional transistors. This has helped the processor to work faster. And due to the increased speed of the transistor, it is possible to increase the clock speed (or frequency) of the microprocessor. So the new generation microprocessor works faster than the previous generation. The architecture of the core processing unit (CPU or core) of the microprocessor has changed a lot over time to what it is today. Added Pipelineing, Branch Prediction, Superscaler Execution, Out-of-Order Execution, Speculation etc. Each core feature further enhances the performance of the microprocessor. In addition to the core micro-architecture feature, cache memory has been added to the microprocessor. The cache can be read quickly by keeping it close to the program’s most widely used data processor. This has further increased the speed of the microprocessor. Multimethreading and multicore technology have been added to reduce the performance of single-threaded CPUs, which is helping to increase the throughput performance of the processor. But at the same time, due to these different features, the chip area of the microprocessor and the use of electrical power have also increased a lot. Which is helping to increase the throughput performance of the processor. But at the same time, due to these different features, the chip area of the microprocessor and the use of electrical power have also increased a lot. Which is helping to increase the throughput performance of the processor. But at the same time, due to these different features, the chip area of the microprocessor and the use of electrical power have also increased a lot.
Transistor scaling has so far helped maintain the trend of increasing the performance of microprocessors in a moderate area and power budget. If we want to increase the performance of microprocessors at the same rate in the next few decades, we should not rely on transistor scaling alone. As the size of the transistor decreases, its threshold voltage decreases, And leakage current is increasing. A large portion of the low voltage transistor power comes from leakage current. The threshold voltage of the transistor cannot be further reduced to limit the leakage current. Then the rate of increase of the speed of the transistor will also decrease. Due to the small dimensions, the density of the transistors on the chip will continue to increase. But the benefits of power and speed are no longer available. The main challenge in the future of microprocessor design is how to use these additional transistors conveniently to increase performance, given the limited size and power budget.
As mentioned earlier, there are two factors behind increasing the performance of a microprocessor, frequency scaling and the addition of advanced design features. The contribution of frequency scaling is declining due to power limitations of transistors. So the reliance on design features to increase performance is increasing. The core of microprocessors is basically made up of logic transistors. The more advanced and complex the features, the more logic transistors are used. So the power demand of the core is much higher. If we just increase the number of cores in the microprocessor and run the core at the highest frequency to increase performance using additional transistors, Then the chip will exceed the power limit. On the other hand, cache memory is much more energy efficient. By reducing the number of cores and increasing the cache memory, the pressure on electricity decreases. A balance between core numbers and cache must be maintained in the microprocessor with a focus on performance and power. That is even more important for future microprocessors. In addition to the microprocessor design of the multicore, multithread processor that we see now, it will continue. However, how this core-thread will be adjusted, given the power budget, may change in the future.
Another new trend in power saving design is hardware customization. This adds an application-dependent hardware engine (or accelerator) to the microprocessor. With these accelerators, many computations, which are traditionally done in software, can be performed much faster on hardware. But it is economical to work separately from the core processor core and as needed. Some examples of hardware accelerators are cryptographic accelerators, media codec accelerators, etc. Another example of hardware customization is the combination of CPU-GPE (Graphics Access Unit). The structure of CPU memory can be made much easier by using GPU for vector data processing. As a result, the CPU can be designed to save energy.
More widespread use of hardware customization will be seen in the future due to the availability of additional transistors through transistor scaling.
A new concept in power-saving microprocessor design is the heterogeneous processor, which will have several large cores for single-threaded performance. And there will be many smaller cores for throughput performance. Core is run at much higher frequencies for single-threaded performance, and many complex micro-architecture features are used, which are logic transistor-dependent. So the demand for large core power is also high. On the other hand, the core for throughput is not so complicated. So the demand for electricity is less. It is possible to further reduce the power consumption by running the small cores at different voltage and frequency levels as per the demand. He has various power management techniques (such as clock gating, power throttling) to make the microprocessor more energy efficient. Therefore, it will be possible to ensure maximum performance in a limited power budget by proper combination of small and large cores in heterogeneous processors.
The last few decades have been the golden age of microprocessor design. Following Moore’s Law, microprocessor performance has increased dramatically. But due to the limitations of technology, it is becoming difficult to maintain that performance in the future. The importance of making the future microprocessor energy efficient has increased a lot. So there is a need to think about the design of the processor. Multicore, Adding to the current trend of multithread processors will be the use of new hardware accelerators. The use of heterogeneous processors will be added to multicore processing. However, in order to get the highest performance by utilizing the functionality of these new design features, the software programming model will also have to change considerably. And with that, new innovations in transistor technology may one day remove the limitations of silicon transistor scaling. And it will be possible to gradually increase the performance of the microprocessor by overcoming the challenges of the current technology. With new technology will come new types of challenges and will require alternative design thinking. The way microprocessor design is evolving to meet the challenges of today’s technology will provide food for new thinking in the field of microprocessor design of new technologies.
Author: Senior Chief Hardware Engineer, Oracle Corporation.
Sources: Shekhar Borkar, Andrew A. Chien, ‘The Future of Microprocessor’, Communications of the ACM, Vol. 54 No. 5, Pages 67-77.