With all the talk on new Solid State Drives and the drive transfer speeds they offer, it’s easy to overlook the time-honored, platter-based hard drive. The fact remains that there is still no better price per gigabyte when it comes to storage than going with the traditional hard drive.
The advances in technology on platter-based hard drives are keeping them as viable data storage devices and, while it may be hard to fathom, today’s 5400RPM drives are even faster than 7200RPM drives from a just few years ago. Why? Spin speed is no longer the single determining factor on platter-based hard drive performance. With the advent of PMR, the areal density of today’s drives is increasing and head movement is faster because the distance to data points is shorter. That probably sounds like a bunch of gobbledygook, so let’s break it down some more…
What is Areal Density?
Also known as bit density, areal density is the amount of data that can be packed onto each platter of the hard drive. The higher the density, the more data. The more compact that data is, the quicker the drive mechanisms can get from bit to bit to read and write data. It is usually expressed in Gigabits per square inch (Gb/in2). Think of it like two people delivering newspapers. Each has the same amount of papers to deliver, each is on a bicycle doing their deliveries.
But one has a route that is very rural with lots of farmland between each house. The other is delivering in a dense subdivision where each house is built right next to each other. Who will finish first? The one that has less area to cover, of course.
Perpendicular Magnetic Recording (PMR) vs. Longitudinal Recording
All electronic data, in its purest form, still breaks down to ones and zeros. Switch on, or switch off. Storing that data long term started with punch cards. Each section of the card either had a hole punched in it (indicating a “zero”) or it didn’t (indicating a “one”). Thousands of cards were needed to achieve the simplest of tasks. Thankfully, we’ve advanced through other methods in which to store data – mainly using tiny magnetic particles lined up on some type of media (whether be tape, cassette, drums, floppy disks, CDs, DVDs, etc.) – on to today’s hard drives.
Think of each piece of data as a teeny, tiny domino tile. One end is positive, the other is negative and depending on which way the tile is facing determines that zero or one. For years, hard drive manufacturers have used a longitudinal arrangement of those dominos lined up all around the platters (as shown above).
Now the technology has developed so that hard drive manufacturers stand each of those dominoes on end – allowing for a higher density. If we take our example literally, it would be like marking each of the dominos on one end rather than on the face of the tile. Stacking this way (as shown on the right) allows many more dominoes (more bits on the drive) to fit on the table. This also reduces the distance from one data point to the next, which means a faster drive.
Isn’t spin speed still important?
Of course it is! Let’s take our two newspaper delivery boys again and mix things up a bit. Let’s give our rural delivery boy a little advantage and rather than a bicycle (a 5400RPM vehicle) we put him on a moped (a 7200RPM vehicle). Now the areal density of the houses really makes a difference in who will finish first. If the delivery route and number of papers is the same, it’s a no brainer – the faster mode of transportation wins.
But let’s give our paperboy on the bike more houses per mile now, and the same amount of papers to deliver – even though the moped is a faster mode of transportation (spin speed) our paperboy on the bike finishes first.
In fact, now let’s have Dad drive him in the car (representing, say, a 10,000RPM spin speed) if all things are even, the car finishes first, but if that car has to go 5 miles to finish and the bike only has to go two blocks, there’s a good chance that bike gets finished first. So areal density makes a huge difference. Right?
Sounds good in theory, can you prove it?
We decided to test out a few notebook drives from just a few years past against drives today. For these tests, each drive was installed in our OWC Mercury Elite Pro mini enclosure and the QuickBench benchmarks were taken over the eSATA connection (capable of up to 300MB/s). Drives that we had on hand for the testing were a 200GB Toshiba MK2035GSS 4200RPM drive and a 100GB Hitachi Travelstar 7K100 7200RPM drive, both only about five years old.
Let’s start with the 4200RPM drive averaging a modest 25MB/s read speeds and 39MB/s writes…
As expected, drive spin speed made all the difference back then as you can see below, the 7200RPM read speeds doubled and increased the write speeds by 25%
That five year old 7200RPM drive with a lower areal density and linear recording technology topped out at roughly 50MB/s read write speeds. Now let’s look at a modern 5400RPM drive such as the 1.0TB Samsung SpinPoint M8. Now, this slower spin 5400RPM drive gives us a data transfer rate over twice as fast as that faster spin 7200RPM drive from just a few years ago.
So what does this mean for me?
While the main benefit to perpendicular recording was originally to fit more data on a single platter in order to create larger drive volumes, the added benefit of faster access means that if you’ve been using the same drive for the last few years, simply swapping the drive to a newer model can make your machine perform much faster.