Imho it depends on context:

For memory (ROM / RAM etc) the 2^x convention applies. 1GB = 1024MB etc.

For background storage (harddisks, USB sticks, optical, tape etc), that used to be true as well. But long ago manufacturers' marketing corrupted this into the decimal 1G = 1000M meaning.

But distinction can be fuzzy sometimes. And subject to abuse. So when in doubt: read the fine print.