o achieve such a huge leap in density, Seagate had to use a technology called heat-assisted magnetic recording (HAMR). Basically, the main issue that governs hard drive density is the size of each magnetic “bit.” These can only be made so small until the magnetism of nearby bits affects them. With HAMR, “high density” magnetic compounds that can withstand further miniaturization are used. The only problem is that these materials, such as iron platinum alloy or a sprinkling of table salt (really), are more stubborn when it comes to changing their magnetism (i.e. writing data) — but if you heat it first, that problem goes away.

HAMR, which was originally demonstrated by Fujitsu in 2006, adds a laser to the hard drive head. The head seeks as normal, but whenever it wants to write data the laser turns on (pictured below). Reading data is done in the conventional way. Just so you understand how small the magnetic bits are in a HAMR drive, one terabit per square inch equates to two million bits per linear inch; in other words, each site is just 12.7 nanometers long — or about a dozen atoms.