Solid state drive (SSD) sales are on the rise, but traditional magnetic hard disk drives (HDDs) are still popular both for home users and businesses alike.

As far as storage is concerned, HDDs are still the cheapest when it comes to price per terabyte, and they’re also much easier to recovery data from. But every year that goes by, these advantages are being lost, so manufacturers are keen to keep up. The first hard disk drive was introduced in 1953 by IBM and since then the storage capacity of HDDs has skyrocketed to keep up with demand.

For decades, HDD manufacturers have used a method known as longitudinal recording technology (LRT) to record data on drives. The magnetisation of each data bit is aligned horizontally, parallel to the spinning disk inside the drive. The issue with LRT is that we are quickly approaching the point when the magnetic grains on the disk become so tiny that they could begin to interfere with each other, losing their ability to hold magnetic orientations; this could render an HDD unusable.

In 2005, Toshiba introduced perpendicular magnetic recording (PMR), followed swiftly by Western Digital and Seagate. PMR bits align vertically and offer a significant increase in areal density compared to conventional longitudinal magnetic recording (LMR) technology, meaning the same surface area can accommodate a lot more data.

PMR is now the standard for recording data to HDDs, but the technology is reaching its limits. The smaller the magnetised domains on the disk are, the shorter distance is needed between the head and surface – and heads are rapidly approaching the point of being as small as they can be made.

The move from LTR to PMR has increased maximum platter density tenfold, to 1000GB per square inch, and we’re now seeing hard disk drives with a whopping 8TB of space. While it is expected that hard drives with a capacity of 10TB will eventually be produced, it’s unlikely manufacturers will be able to downsides the heads any more.