Terabyte hard disks on the horizon

The first computer I bought almost exactly 20 years ago had a disk capacity of 720 kB. It was provided by a so-called high-density floppy drive. Somewhat later I added a 40 MB hard disk in 5.25” installation size, which was absolutely lavish for a home computer. Today (mid 2006) the largest commercially available hard disk has a capacity of 750 MB which is roughly one million times that of a 720 kB floppy, or twenty thousand times larger than my first hard disk. The current street price for a 750 GB hard disk is at $400 USD.

This development shows that the 1024 MB hard disk is around the corner and we will soon have to get used to another SI unit called terabyte. In fact, the SI quantity “tera” is misused here, since it refers to the decimal power 10^12, or one trillion, whereas the number of bytes on a terabyte hard disk is actually the power of two 2^40, which amounts to 1,099,511,627,776 bytes.

The IEC has devised the cute sounding name tebibyte for this number in conjunction with gibibyte, mebibyte, and kibibyte for the lower binary quantities. The IEC denomination turned out to be not very popular, however. Have you ever heard anyone speaking of a gibibyte hard disk?

The etymology of the SI quantity specifiers is likewise interesting. They all go back to the Greek language. “Kilo” originates from the Greek khilioi meaning thousand, “mega” comes from the Greek megas which means great or mighty; “giga” or Greek gigas meant giant, and finally tera is the Greek word for monster, which is probably an apt description for a hard disk that large.

Before the monster disk becomes available, there are some technical challenges to master, in particular the challenge of the superparamagnetic effect. The industry’s answer is currently perpendicular recording which aligns bits vertically to the disk surface.

An even newer technology -currently in research state- is heat-assisted-magnetic-recording (HAMR), where a laser beam or a similar energy source heats the disk surface while recording bits. This reduces the required strength of the magnetic field and magnetisation can thus be achieved at a higher density.

There is a problem, though. The disk’s lubricant unfortunately evaporates at these temperatures, which is why the industry is now researching self-lubricating disks that use embedded nano tubes to store replacement lubricant. This technology would allow multi-terabyte hard disks to become a reality. This is probably just a few years away from us.