Misc: What not so hep disease had its virus finally identified in 1984?

Questions

Computers - what is the web program "web crawler" used for?

Computers - what key on the keyboard "shifts" the alphabets keys to "uppercase"?

Computers - what year was the first IBM pc introduced?

Computers - when software stops responding & your computer freezes, what has happened to your computer?

Computers - which drive is mostly the "main drive" on a pc computer?