The laptop stores instructions and data in the form of 0s and 1s that are
recorded on the surface of the platter as tiny magnetic points; to read back
the information, the read/write heads look for changes in the polarity of the
dots. The hard drive does not decode the meaning of the 0s or 1s; it is just a
pick up, storage, and delivery mechanism to the computer’s microprocessor.
The read/write heads are almost all variants of the same simple design first
developed for use with magnetic audio tape: turns of tiny copper wire circle a
ferrite(a form of iron oxide, once again) leaving a tiny gap on the side of the
head that faces the platter. When electrical current is passed through the
coil, it leaves a tiny magnetic marking on the data surface.
To read the information, the current is turned off, and the same gap senses the
magnetic markings — actually the transition from one polarity to another —
as it passes over the disk. The drive includes a tiny amplifier and a rectifier
that converts the information into precise digital 0s or 1s.
How big is that hard drive in the window? .....................................
Designers of laptops and personal computers sometimes use the sort of fuzzy
math that would make a politician proud. Some real numbers exist when it
comes to capacity, but they are often hidden behind technological and mar-
keting bafflegab.
Here’s an example: Exactly how big is a 10GB hard drive?
In precise technical terms, a gigabyte of information is equal to 2^30
power, or 1,073,741,824 bytes.When the marketing department at a hard drive manufacturer (or a com-
puter seller) describes the capacity of a drive, they often use a shorthand
definition of gigabyte that means 1 billion bytes: 1,000,000,000. In that
case, a marketer’s 10GB hard drive is actually a 9.3132GB device, about
7 percent smaller.
Back to technical specs: The hard drive has to devote some of its space
to the index of files as well as electronic markings that denote the
tracks, sectors(portion of a track), and clusters(groups of sectors). And
if the hard drive is the boot diskfor your system — the one that loads
the operating system when the laptop is turned on — space also has to
be left for that purpose. All told, the overhead required by the computer
to manage the hard drive can range from 10–20 percent; pick the middle
point and call it 15 percent. The supposed 10GB drive that is actually a
9.3132GB device may actually only have room for 7.9162GB of data.Chapter 7: Easing In to Hard Disks 119