Saturday, February 11, 2006

Hard Drive Densities

There are only a few ways to get more capacity in a hard drive.

1) Larger platters (physical size). Not really an option for most applications as the larger platters lead to larger seek times. Which is one of the reasons that the old 5.25" HDDs went out of vogue (they had 20-40ms seek times). The 3.5" drives typically have 8-12ms seek times and 2.5" drives are even faster (3-5ms).

2) More platters. Some drives pack 5+ platters into each unit, with up to 10 heads (one on each side of the platter). After a certain point, you run into a roadblock. The platters can't be made any thinner and you can't pack the platters any closer together.

3) Areal density. This is the number of bits that you can store per square inch (or square centimeter, 1 square inch = 6.4516 square centimeters). Most gains in capacity come from increases in areal density. However, even with GMR, they've run into a roadblock where you can't store the bits any closer together without them starting to interfere with each other. Future drives will use a technology called PR (perpendicular recording) which allows more areal density without this problem. PR is expected to boost capacity up to 5x over GMR technology.

Areal densities:

1998 - ~12 gigabits/sq in
1999 - ~25 gigabits/sq in
2000 - ~60 gigabits/sq in

GMR was expected to top out at 75 gigabits/sq in, but even today, most drives being manufactured are only 60 gigabits/sq inch. That's the main reason that hard drive sizes seem to have stagnated for the past few years.

PR drives are finally shipping (nearly 4 years after being demonstrated back in 2002). Their starting density is 100-130 gigabit/sq inch. Expected maximum density should be around 230-245 gigabits/sq inch. That's about a 4x gain over what we can cram into a 3.5" drive today.

As a rough guess, we should see 600-800GB drives soon with drive sizes topping out just shy of 2TB in a 3.5" package before we hit the wall again.

Labels: 2006

posted by Wuphon's at 12:14 PM