Hardware Reference
In-Depth Information
Performance
When you select an HDD, one of the important features you should consider is the per-
formance (speed) of the drive. Hard drives can have a range of performance capabilities.
As is true of many things, one of the best indicators of a drive's relative performance is
its price. An old saying from the automobile-racing industry is appropriate here: “Speed
costs money. How fast do you want to go?”
The speed of a disk drive is typically measured in two ways:
Transfer Rate
Thetransferrateisprobablymoreimportanttooverallsystemperformancethananyother
statistic, but it is also one of the most misunderstood specifications. The problem stems
from the fact that several transfer rates can be specified for a given drive; however, the
most important of these is usually overlooked.
Don't be fooled by interface transfer rate hype, especially around ATA-133 or SATA-150/
300/600. A far more important gauge of a drive's performance is the average media trans-
fer rate, which is significantly lower than the interface rate of 133, 150, 300MBps or
600MBps. The media transfer rate represents the average speed at which the drive can ac-
tually read or write data. By comparison, the interface transfer rate merely indicates how
quickly data can move between the motherboard and the buffer on the drive. The rota-
tional speed of the drive has perhaps the biggest effect on the drive's true transfer speed;
in general, drives that spin at 10,000 rpm transfer data faster than 7,200 rpm drives, and
7,200 rpm drives transfer data faster than those that spin at 5,400 rpm. Note, however,
that rotational speed is not the only thing to consider—the track linear density plays a
huge part in performance as well. For example, the 5,400 rpm 500GB drive in my current
laptop has a maximum transfer rate of 118MBps, whereas the 7,200 rpm 60GB drive in
my previous laptop has a maximum transfer rate of only 44MBps. That means my newer
5400 rpm drive is actually more than 2.6 times faster in actual transfer rate performance,
eventhoughitspinsover33%moreslowly.Ifyouarelookingforperformance,besureto
check the true
media
transfer rates of any drives you are comparing.
The confusion results from the fact that drive manufacturers can report up to seven differ-
enttransferratesforagivendrive.Perhapstheleastimportant(butonethatpeopleseemto
focus on the most) is the raw interface transfer rate, which for SATA drives is 150MBps,
300MBps or 600MBps, and up to 100MBps or 133MBps for older PATA drives. Unfortu-
nately,the drives actually read andwrite data much more slowly than that; youmust usea
high-performanceSSDinsteadofatraditionalharddiskifyouwanttofullyexploitSATA
