3.6ns RAM is rated to run at 555.56MHz (277.78MHz)
Here's how to figure it out. A MHz is one million (1,000,000,000) clocks per second. The nanosecond rating is the delay between cycles. Therefore, one simply divides one billion (a nanosecond, after all, is one billion
th of a second) by the nanosecond rating for a Hz rating. Divide by a million to get the MHz rating.
Or, you could simply divide 1000 by the nanosecond rating.
