Hardware Reference
In-Depth Information
those few that did for other reasons. Some cube-style Mini-ITX cases provide
one 3.5” drive bay, and a few provide two or more. If the case you choose has
a 3.5” drive bay and you require significant storage capacity, installing a quiet
desktop 3.5” hard drive is by far the most cost-effective decision.
Nearly all Mini-ITX cases include one or more 2.5” drive bays. Mainstream 2.5”
laptop hard drives are available with capacities up to 1 TB and rotation rates
from 4,200 to 7,200 RPM. A few 10,000 and 15,000 RPM models are available,
but their prices are outrageous, their capacities small, and their heat produc-
tion and noise prodigious. The price, capacity, and performance of laptop hard
drives are closely interrelated: the largest drives are expensive and slow, the
fastest drives are expensive and small, and the least expensive drives are small
and slow.
A typical laptop 2.5” hard drive has half the capacity of a 3.5” desktop hard
drive that costs the same, and runs at 5,400 rather than 7,200 RPM. You pay
that premium for the smaller physical size and lower power consumption.
Read and write speeds are closely matched and vary from moderate to high
depending on the type of drive. Laptop hard drives have a reputation for un-
reliability compared to desktop hard drives, but in all fairness that's probably
because they are typically used in poorly ventilated laptop systems that are
much more likely than desktops to be dropped or shocked. If the case you
choose does not accept a 3.5” hard drive, the most cost-effective choice is a
2.5” hard drive in whatever combination of capacity, performance, and price is
best for your needs.
Solid-state drives debuted in consumer systems as very expensive options for
high-end notebook systems, but they are becoming increasingly common in
Mini-ITX systems. Their advantages are obvious: high performance, low power
consumption (and heat production), and completely silent operation. SSDs
are available in many form factors, including some units that can be installed
in a PCI slot, leaving a drive bay available for another drive.
With the exception of their very high price per gigabyte, the disadvantages of
SSDs are less obvious, but worth considering. First and foremost, SSDs wear
out as they are used. Consumer-grade multi-level cell (MLC) SSDs are gener-
ally rated for one to two million write cycles (1,000 to 10,000 writes per cell)
and professional-grade single-level cell (SLC) SSDs for about five million write
cycles (100,000 writes per cell). Even with wear-leveling enabled and a large
allocation of spare sectors, the capacity of any SSD gradually decreases with
use as more individual cells become unusable.
The performance of SSDs is a mixed bag. Excluding the least expensive mod-
els, a new SSD generally offers noticeably faster read performance than a hard
drive. In particular, random reads are much faster because there are no heads
to be moved and zero latency. Writes are much slower than reads, however,
and write performance declines as the drive ages, even if the operating sys-
tem fully supports TRIM (as do Windows 7 and recent Linux releases). In some
cases, write performance may degrade sufficiently to cause the system to ap-
pear to hang for a second or more while a write is completed.
Finally, although it's not an issue for most people, it's impossible to securely
wipe an SSD. Well, at least if you expect the drive to be usable after it's wiped.
