today are half again as wide, at 0.85 inches; the first such devices have capaci-
ties of as much as 4GB. Stop and think: That’s less than an inch square and
smaller than a postage stamp. The first uses of this sort of tiny drive are
expected to be in cell phones, digital audio players, PDAs, and digital cameras.
Designers (and buyers) are continually clamoring for drives to be lighter for a
real reason: Their shoulders and backs hurt from dragging around 10 pounds
of laptop, power adapter, and other accessories. Every ounce that can be
trimmed from a laptop gives the marketing department something else to
brag about.
Current 2.5-inch notebook hard drives weigh somewhere near 100 grams, or
about 3.5 ounces, an amazing feat of productive shrinkage. As this book goes
to press, makers including Toshiba offer 1.8-inch-wide drives with a capacity
of as much as 60GB and weighing just 62 grams, or just over two ounces. And
the same company’s 0.85-inch 4GB device weighs 10 grams, or about a third
of an ounce. (You would have to stack about 45 of these drives atop each
other to come up with a pound’s worth of electronics.)
Because laptops are intended to be powered at least part of the time by a
rechargeable battery rather than from AC wall current, another important
specification for a hard drive is its power consumption. The less power
required by the hard drive, the longer the battery will last, or designers can
try to get away with a battery of a smaller capacity. And the more wattage a
hard drive demands, the more heat it generates within the case, and that
must be exhausted by a fan, which itself draws power.
A modern 3.5-inch hard drive for desktop and tower computer usage spins at
7,200 or 9,600 rpm and requires a 5-volt power source; at startup it draws as
much as 10 to 11 watts. A typical 2.5-inch internal laptop model, with 100GB
storage, spins at 4,200 rpm and requires 5 volts. At startup, the power draw is
typically about 4.5 watts, dropping to about 2 watts for reading and writing.
Toshiba’s 1.8-inch 60GB drive, which spins at 4,200 rpm, requires only 3.3 volts
and demands as little as 1.2 watts to start up and 1.4 watts for reading and
writing. And the tiny 0.85 drive has about the same miniscule power demands,
although it spins at only 3,600 rpm and currently has not gone past 4GB in
capacity.
Other than size, weight, and power demands, a laptop hard drive is very
similar in design to a desktop drive. The fact that they are small does require
some tradeoffs, though. For example, a typical 3.5-inch drive may have as
many as four platters, a laptop drive may have only one or two; coupled with
the smaller size of the platter itself, this reduces the portable drive’s maxi-
mum capacity.
Chapter 7: Easing In to Hard Disks 115