These days, most Americans the word "data" as a mass noun, like water, happiness, air, love, food, etc.
Originally, a "datum" was one single piece of information, and the plural of "datum" was "data." People actually said, "Our data ARE very carefully protected." But since the dawn of the computer era, no one uses the word "datum" anymore. When they talk about "data," they mean all of the data, or at least the entire collection of data that is referenced in the conversation.
Frankly, although most of us still remember the word "datum," we're rather confused about its usage. Is my birthday (1943-08-31) a datum? Probably yes.
Is the Japanese surrender at the end of World War II a datum? Perhaps not.
I cannot recall the word "datum " (and I am a pre computer dinosaur) but I was always aware that "data" was a plural form.
However, I think it is acceptable for collective nouns to be treated either as a singular or a plural quantity.
http://data.grammarbook.com/blog/si...ect-and-verb-agreement-with-collective-nouns/
Also "data" can be thought of as either a collective noun or as a simple plural. (eg it can be "data" or "the data")