I would like to know how was counted 1 second in computers. I mean how machine can understand period of 1 second. Who and when resolved this problem, and more important how ?
Basically, the computer has a "clock". This is a chip that generates a pulse every fixed period of time, say, every 1 millisecond, generated usually via a crystal.
Counting second (or any long enough time) is now simple - the computer can count the number of "clock ticks" to estimate the time that has passed. If the external clock signal has a pulse every 1 millisecond, then after $10^6$ such pulses, about 1 second has passes. This is not precise, because the computer takes some time to count each pulse, but such an impreciseness is order of magnitudes smaller than milliseconds.)