The word data is more often used as an uncountable noun with a singular verb than as a plural noun with singular datum.
It's like "hair". You can hold a single 'hair', you can also hold three hairs. But if you're looking at an entire mane, you ain't counting, so it's referred to as "hair" again.
Yeah, but for example, IEEE conference paper templates explicitly state "The word 'data' is plural, not singilar". So if you use it with a singular verb you will receive this post in an email and you can only say thank you and change it.
I guess I tend to use data as a mass noun when referring to computer data ("there's a lot of data on that drive") and as a regular noun when referring to data in the scientific sense ("these data show xyz")