How are PC components bought in bulk handled compared to components bought individually?

Bulk components used for manufacturing come on reels of thousands not individually

Comment: I used to work in a manufacturing place, where we assembled computers. The answer from Marvinator is spot-on. His disk drive example is what we saw for disk drives,  memory, expansion cards, and other components.

One model computer we were assembling had an infrared sensor. The company that sold that sensor didn't offer bulk packaging. We received the kind of boxes a retail store would receive: Each censor was in a plastic package, ready to be put onto the sales floor. We had to open thousands of those packages, and take out a USB cable, driver & software installation disk, and printed instructions when all we wanted was the sensor. 

When you buy bulk, they are usually shipped in bulk packaging.  Individual items come in their own packaging.  This may seem a bit confusing but let me see if an example can help.  We bought hard drives in bulk for our office. We got in large boxes that had drives in their own compartments, separated by Styrofoam.  Each box had about 20 drives.  When you buy a single drive, retail, it comes in it's own box, with it's own Styrofoam, made for one drive.  A second example is when we purchased a large quantity of mice. We received a large box with all the mice in retail packaging, complete with the hole that they would be hung on a peg in a retail store. 

Now, this does not mean you will get EXACTLY what we did.  You may want to order 10 or 20 of an item and you might get a big box with 20 smaller boxes in it, each item packed in it's own box.  It really depends on the company you purchase from.