During my time spent working with multiple machines, I have noticed that performance of the same machine doing the same tasks in the same order differs and sometimes the difference is big enough to be noticeable. This applies to all the machines I've owned and/or maintained (old and modern). Some examples (many of them you may have noticed yourself) that sometimes are completed in different time frames:
Hardware tests and operations (usually executed within a customized OS such as one of the many DOS variants), HDD tests and "low level" formats
Software installation or other tasks (such as benchmarks) within a general purpose OS (Windows, Linux, etc)
I can imagine this is caused by the fact that a machine is built with many components having to communicate as a whole and since the mechanical and electronic parts aren't perfect the overhead occurs. In the last example, I assume the OS complexity and concurrently running multiple processes has some additional effect as well. However, I'm wondering if this hardware imperfection and overhead is indeed that high to be humanly noticeable? Maybe there are other factors that are influencial as much or even more? So, in short - why?
Actually, it doesn't matter: laptops, desktops, etc. OS doesn't really matter either. Btw, I'm not comparing machine to machine. I'm just saying that the same tasks on the same machine sometimes take noticeably different time to complete (the difference is usually small, but still noticeable).
there will be variations as no 2 pc's are ever the same might be the same spec but one could have a better binnned cpu or motherboard
You still didn't understand the question. I am not comparing separate machines. I'm comparing results on the SAME machine. And from my experience this applies to ANY machine.
Just to give you a simple example - if you did OS installation multiple times (say, 20) on the same computer, record the times taken and then compare them, you'd see the difference in them. This applies to any computer.
you didn understand my answer there are different stepping of cpu's as a cpu evolves you get an c0 and d0 stepping i7 920 the d0 will be a lil faster then the c0 nothing greatly notable but there is or for in stance a core 2 from earlier and one thats gone through some evolution, even though its the same model the one will be a bit faster same as for mother boards there might be a board that has a minor capacitor problem nothing that affects the working of a pc but it might still affect a pc's performance