A recent twitter discussion via Doctor Karl led me to the question of whether it matters that while large capacity desktop drives spin anywhere between 7200RPM and 15,000RPM, most large capacity laptop drives spin at only 5400RPM.
For years, 5400RPM was the standard speed of a hard drive, back when 1GB and 2GB were huge. The speed demon server drives that came out shortly thereafter were 4GB and 9GB 7200RPM drives, and required active cooling so they didn’t melt from the heat. Everyone understood that 7200 RPM was faster, because it delivered your bits quicker.
Fast forward ten years, and you can get 1TB and 2TB hard drives spinning at 7200RPM, and smaller laptop drives at 500GB and 1TB spinning at 5400RPM. (You can also get 600GB drives spinning at 15,000 RPM, but that’s today’s bacon-cooker for servers.)
But is the 5400RPM laptop drive really slow?
I would argue it’s not. Areal Density increases as drive capacity goes up; and today’s 3.5 inch and 2.5 inch drives aren’t physically bigger than the same size drives of the past, meaning their areal density has gone way up (see some examples on Wikipedia’s Memory Storage Density page).
This means that when a 1TB disk makes one revolution (in 1/5400th of a second), it’s picking up much more data from the platter than, say, an 80GB disk spinning at 7200RPM is after a single revolution in 1/7200th of a second.
Granted, you’ll still get faster performance out of a 7200RPM drive than a same-sized 5400RPM drive, but it’s not the end of the world to pick the slower-rotating disk. It also won’t get as hot as the faster one.
Now keep in mind, too, that these speeds are talking about sequential or mostly-sequential data access, when you start at one point on the disk, and read continuously to a later point, like playing a record or a CD. Unless you’re playing audio or video, most data access isn’t like this. And that kind of performance — operations per second — hasn’t increased much over 20 years. But that’s another post.