To answer correctly we need a scenario, because there is nothing like absolute answer when thinking about IT speed.

The speed is usually taken at the end of an operation, for example a reading time needs a seek time + an access time, and typically none is linear on a normal rotating hard drive ( cf. https://en.wikipedia.org/wiki/Ha... )

In 2015 an average seek time latency is around 10 ms for hard drives.

On the other hand an average DDR3 has an access latency of 10 ns ( cf. https://en.wikipedia.org/wiki/DD... )

So based on those values, we can conclude that the average seeking time of data in memory is roughly 1 000 000 times faster than accessing it from a hard drive.

This ratio started to change only with the arrival of SSD disks.