IBM's discovery of "pixie dust", a microscopic layer of the element
ruthenium just three atoms thick, has prolonged the active life of
the disc drive - but for how long? writes Nicholas Enticknap.
We tend to take disc technology for granted, but a pause for
thought shows that the progress storage engineers have been making
over the past decade is truly staggering. In 1991, peak packing
density was 90Mbits per square inch, and the largest available
drive capacity, using 11in platters, was under 6Gbytes. Today peak
packing density is 25Gbits per square inch, and the largest
available disc drive, using 3.5in platters, is 75Gbytes.
That represents a 75% improvement in packing density every year for
more than a decade. It is hard to think of any other technology
that has been improved at such a rapid rate.
This development has made possible the doubling of storage capacity
experienced by most users over the past few years, as they have
adopted new wave applications such as enterprise resource planning,
customer relationship management, datawarehousing and e-business.
Advances in disc technology have been the fuel that has powered the
Internet boom - it could not have happened without them.
Disc drive sales in 2000 were estimated by Gartner Dataquest to be
$32.4bn (£23bn). This amount of storage would have cost 40 times as
much 10 years ago - over twice the gross domestic product of the UK
- and, clearly, that would have been impossible.
But what about 10 years from now?
To sustain the progress the industry has made during the past
decade, packing densities would have to rise to 4.7Tbits per square
inch by 2010. That looks unlikely, to say the least.
Commenting on IBM's new antiferromagnetically-coupled (AFC) disc
technology, which uses the pixie dust layer, IBM storage technology
division communications manager Kim Nguyen said, "We were looking
at a barrier coming up very quickly. What pixie dust does is allow
us to push the paramagnetic effect out for at least two or three
years."
The paramagnetic effect is what will ultimately prevent storage
engineers increasing the packing density any further. In theory,
there is a limit to how small domains of magnetism can be made, any
smaller and they will be unstable and therefore useless for
recording information.
What nobody knows is what the minimum size of a stable magnetic
domain can be, and estimates are constantly being revised
downwards. Gartner analyst Josh Krischer said, "A few years ago we
thought the paramagnetic limit was 35Gbits per square inch. Today
we place it at over 100."
We will almost certainly push it beyond 100, but 4,700 looks way
out of reach. If the limit had been 35Gbits per square inch, disc
technology development would grind to a halt within a couple of
years. Before the discovery of the pixie dust effect, IBM's disc
drives had packing densities in the range of 15 to 20Gbits per
square inch, so just one more doubling of capacity would have
bought us right up against the theoretical limit.
AFC technology has allowed IBM to push today's state of the art up
to 25Gbits per square inch, as implemented in the Travelstar 48GH
drive introduced at the end of March, which yields a 2.5in disc
capacity of 48Gbytes.
IBM believes it can push capacity up to 100Gbits per square inch by
2003 which will yield a desktop 3.5in disc capacity of 400Gbytes, a
notebook (2.5in) capacity of 200Gbytes, and a microdrive (1in)
capacity, for handhelds and mobile phones, of 6Gbytes.
Is that the limit? Nobody really knows. According to Nguyen,
scientists still have a couple of other ideas to pursue which may
push the ultimate limit beyond 100Gbits per square inch. Whether
they can do it or not, the industry is very relaxed about the
situation. There have been so many technology advances in the
half-century history of IT that it seems inevitable that another
one will come along when it is needed.
"Once the paramagnetic limit is reached,we will get new technology
such as holographic storage. So don't worry about the technology of
the disc," said Krischer.
IBM's increasing disc densities
Disc packing density
has increased from 200,000 bits per square inch on the first disc
drive, IBM's Ramac of 1956, to over 25 billion bits per square inch
today. Progress has been uneven, as this chart of leading-edge IBM
disc technology shows. In the 1970s density increased by 32% a
year. In the 1980s, growth was 17% a year. But, in the 90s, the
discovery of first the magnetoresistive and then the giant
magnetoresistive effect accelerated progress. Capacity increased by
75% a year. If progress continues at this rate, packing density
will be 4.7Tbits per square inch in 2010.