Does the frequency of machine effect execution time of my code?

I have written code which performs a specific task; now when I will run on different machine(having different frequency) will it take different time?

Ouestion

If my code has one printf function, then will its required number of machine cycles be fixed for all machines, or will it depend on the system?

My system frequency is 2.0GHz, what does it 开发者_如何学Gomean?

The performance time of the code will depend on the frequency of the CPU, amongst many other things. All other things being equal, a faster CPU will take less time to execute the same instructions. But the number of other things that can affect the timing is vast, including O/S, compiler, memory chips, disk and so on.

If the machines have the same basic architecture, then the number of machine cycles is fixed. However, modern CPU architectures are very complex, and there could easily be variations depending on what else is running on the machine at the same time. If the machines have different chip types (even within a family such as Intel Core 2 Duo), then the results could be different. If the machines are of different architectures (Intel vs SPARC or PowerPC, say), then all bets are off.

If the 'frequency is 2.0 GHz', then it means that the main CPU clock cycles at 2.0 GHz. How many instructions are executed in that time depends on the instructions, and the parallelism (how many cores), and the CPU type, etc. The CPU frequency is separate from the bus frequency which controls how fast memory can be read (so, I'm using a 2.0 GHz CPU but the memory bus runs at 1067 MHz).

Clock speed of a computer of course has its influence on the execution time of a program, but just stating that the processor runs at 2 GHz is absolutely not enough to determine how long exactly the program will run because there are huge differences in "efficiency" between the processor families - an Intel Core family processor will just do a lot more work per time unit than its predecessor, the Pentium 4, when both run at the same speed.

So yes, CPU speed has a serious influence on the execution time of a program but just the GHz value is absolutely not enough. That's why various benchmarks were set up, to be able to compare the work a processor can do in a time unit. These benchmarks will run a mix of instructions that can be considered a typical workload in a chosen scenario, and time how long their execution will take. Check out Whetstone and Dhrystone for some older but relatively easy to understand benchmarks.

The fact that there are tons of benchmarks only proves that it's not easy at all to obtain a comparable value on whose relevance everybody can agree, it remains a topic for debate...

The frequency of the CPU defines how much work it can do within a certain time. The code is the same on all machines (i.e. it's compiled code) so yes the frequency will affect the time it takes to run your program.