On page 133 of the SI brochure, the International Bureau of Weights and Measures says, “The numerical value always precedes the unit, and a space is always used to separate the unit from the number [...] The only exceptions to this rule are for the unit symbols for degree, minute, and second for plane angle.” (emphasis added)

By those standards, 3.06 GHz, 500 GB, and 1.44 MB are correct. 3.06GHz, 500GB, and 1.44MB are wrong — but so many places have been doing it wrong for so long that it’s almost become common practice.

Common Practice: 32GB looks better.