How does the class (Random) generate random numbers?

If the class Random uses the current time, how can it generate a lot of random numbers within the same millisecond?

I wrote a code that generates random numbers using the current Time with accuracy up to millisecond, but when I test the technique in the loop, it keeps generating the same number for about ten times, but If I use the class Random, it generates random number even in the loop.

So how as there is nothing less than millisecond in the computer time? If it doesn't use the current time, what does it use?

Thanks!