Moore's Law
When the price unchanged, the integrated circuit can accommodate the number of components, it will increase approximately every 18-24 months doubled the performance will also be doubled
CPU are based on long-term rapid exponential increase, but in recent years, CPU clock speed has remained at around 4G Hz, can no longer be further enhanced. Moore's Law gradual failure
Amdahl's Law boarded the stage of history
Amdahl's Law
The main contents of Amdahl's Law is more the processor, the faster the speed of execution, but there is a limit.
The more the processor, the faster execution speed is obvious, the more CPU resources can do, we have a task to execute multiple CPU speed of the faster, of course,
A faster is limited, it is impossible to infinitely improved.
This limit means: for example fish, growing from a big fish fry into the speed is definitely not affected by the number of fish ponds, as this type of task is known as a serial task.
Serial task no matter how many CPU resources we are unable to improve the speed of
Most of the program, most of the tasks are all part of the serial and partially parallel, a certain proportion of serial and parallel ratio, the difference is that different proportions of these different tasks.
If the program is particularly high proportion of parallel, multi-threaded at this time will be able to play a better role. But if the program is a purely serial, which is his code only in the past
Perform back line by line, then the time multithreading can not bring us help. So the meaning expressed by the ratio figure is parallel to what percentage of the time, you can most
How many times reached the final upgrade.
Lowest blue line parallel proportion of 50%, two times from zero to stop eventually rise to the beginning, because only 50% of the code can be parallel.
But the proportion of parallel top green curve is 95%, the anti speaking is only 5% of serial sections so since in the limit can be up to 20 times improvement.
This is known as Amdahl's Law.
In the future, we slowed for a CPU upgrade, which requires us to be more parallel part in parallel with the program, in this way to improve the performance of the program
