One of the things that impress me is the evolution of technology around hard drives. I bought my first hard drive when they cost around 1/3 or so the cost of the actual computer. The first HD I added to a computer was a 20 meg external SCSI drive. I had just gotten a Macintosh SE with a 20 meg internal HD and added an external one. The external HD was a loaner from the company I was working for; they wanted me to test it out and see if it would do the job.
It was slow, but it did what we needed (moving a large set of files around). At the time of the first hard drives appearing I had between 1200 and 1500 floppy disks (the 3.25 disks not the much older 5.25). We used to have two floppy disks so that we could have the OS and Applications running on one drive and the memory of the computer with the other drive having the files we were using. The summer I built a HyperCard Dinosaur Stack with my students we used 24 disks to run the entire stack. Swapping those disks was painful, having a hard drive changed everything.
The funny thing about the HD’s of then and now is that I have more memory on my phone now than I had in a computer until the late 1990’s. External drives have become so much easier to use now. USB connected hard drives are a breeze. I am a fan of the Western Digital (one of the few surviving hard drive companies) USB 3.0 external drives. They have 7200 rpm drives and 5400 rpm drives.
For the most part and for most people the 5400 rpm drive is perfect. That is the speed at which the platter spins inside the drive, honestly unless you are moving massive amounts of data every day (a terabyte or more per day) having a 5400 rpm drive is all you need. With the new USB 3 connections, you have plenty of speed to move the average amount of information around (100 megs or so per day or less).
Hard drives have become amazing tools!