The alternative would be M.2, the slim strip type you'll find in modern Notebooks and some PCs. As you mentioned an Atomos, you likely want a 2.5' SSD. Now, SSD also come in two typical form factors. No need to add drive to that, the D stands for drive. As you also wrote SSD shortly after in your original post, I guess you only meant to write SSD.
You write harddrive, which is a term usually referring to mechanical spinning drives. Click to expand.It is hard to understand what exactly you want.
