The information was being copied to the hard disk, not the other way round, so no a 1 TByte hard disk was not being used by the White House in the late 90s.
The process is called electronic document management. You have all these pieces of paper taking up masses amounts of storage space. So the answer is to keep all the pieces of paper and scan them into an intelligent electronic document management system that's too complicated for your average person to figure out how to use. What that does is (with masses of human-input) is create databases of information with document readers for each type of file being stored.. and absolutely nothing that solves the storage problem all that paper caused.
Queries then retrieve the data and the relevant reader will be used to view it automatically. The system we use at our Dept of Transportation cost about $30K, has mirror sites around the state (connected via fiber) and keeps track of all documentation related to projects dating back to the 60s.
Nowadays that includes email and word processor documents associated with projects (usually converted to pdfs but there are other possible formats) as well as your regular dwgs.
Older projects have had the letters and legal paper work scanned and converted to pdfs, and paper drawings scanned and converted into dwgs.
Naturally we use network appliances to store the data, usually made up of multiple 1/2 or 1 TByte disks, with built in redundancy and repair.
So there you have it. The most likely scenario is that this unsecured hard disk was the end product of electronic document management and as such should have had encryption built in.
None of the data we store is unencrypted even though we don't keep anything that you'd normally associate with requiring security. I mean the huge fucking road or bridge we built is a bit of a giveaway, not usually something you can pretend didn't happen. Of course the number of government systems with default usernames and passwords left unchanged are another story. But I'm sure admin / admin won't work.. well pretty sure... well I'm hopeful.. shit it's going to work isn't it?