PACK YOUR BAGS
Data travels over an Ethernet network in
packets called frames. A frame consists of
a MAC header (consisting of the source and
destination MAC addresses and the Ether
type), the data (or payload), and a CRC
checksum. The Ether type identifi es which
protocol is being transported inside the frame
(e.g., Internet Protocol); the CRC checksum
detects any alteration that might have oc-
curred during transmission. A jumbo frame is
an Ethernet frame carrying more than 1,500
bytes of payload.
The original Ethernet cable had a shielded,
coaxial design with a BNC (Bayonet Nut Con-
nection) at each end. This single cable was
shared by every computer on the network.
Ethernet networks using unshielded twisted-
pair wiring were developed in the mid 1980s.
This enabled the network to operate in full
duplex mode, meaning data could fl ow in two
directions simultaneously. Although the wir-
ing is unshielded, the twist design blocks most
interference (provided the cable is not run in
close proximity and parallel to electrical wir-
ing). Twisted-pair wiring, which is terminated
with 8P8C jacks, is also much less expensive to
deploy than coax.
The most common Ethernet cable is
known as Category 5 (Cat5). It consists of four
pairs of twisted wires inside a single PVC jack-
et and can support data rates up to 100Mb/s.
Cat5 has since been superseded by Cat5e (the
“e” stands for “enhanced”), an improved speci-
fi cation that is capable of supporting data rates
up to 1Gb/s. Both types of cables can operate
at frequencies up to 100MHz and are limited
to runs of 100 meters (328 feet), including
the length of patch cables used at each end.
Ethernet networks based on this technology
(combined with a hub or switch) are known
as 10BASE-T (speeds of 10Mb/s), 100BASE-T
(speeds of 100Mb/s), or 1000BASE-T (speeds
of 1Gb/s).
Category 6 (Cat6) cable also consists of
four twisted pairs of wires and is backward
compatible with Cat5/Cat5e installations,
but it features more stringent specifi cations
for crosstalk (interference caused by the
signal transmitted on one channel bleeding
into an adjacent channel) and system noise.
Cat6 cable can operate at frequencies up to
200MHz and is capable of supporting data
rates up to 10Gb/s, but it is still limited to runs
of 100 meters.
The Wi-Fi standard operates on the exact
same principles as wired Ethernet, with the
obvious exception that the data is transmitted
over the airwaves instead of cables.
AUTOPSYHP Touchsmart IQ770
We pried open HP’s Kitchen PC to see what makes it tick. We wanted
to expose its touch screen, but doing so would have destroyed the
machine in the processhttp://www.maximumpc.com | JUL 08 |MAMAMAXIMXIMXIMXIMUUUUMMPPPCC| 63
SUBMIT YOUR IDEA Ever wonder what the inside of a power supply looks like?
Don’t take a chance on destroying your own rig; instead, let us do the dirty
work. Tell us what we should crack open for a future autopsy by writing to
[email protected].HARD DRIVE
HP tucked a 320GB SATA
hard drive in a bay inside
the part of the aluminum
chassis that the display is
mounted to.OPTICAL DRIVE
A low-profi le, slot-fed 8x SuperMulti DVD
burner—with HP’s LightScribe technology—is
squeezed into the lower chassis, above what’s
basically a notebook motherboard.CPU
HP chose a mo-
bile CPU—AMD’s
dual-core Turion
TL-52, clocked at
1.6GHz—to mini-
mize the need for
cooling. As you
can see here, the
chip is cooled by a
heat pipe instead
of a fan.VIDEOCARD
The IQ770 is no gaming power-
house, but it does feature a dis-
crete videocard: Nvidia’s GeForce
Go 7600 clocked at 445MHz, with
256MB of GDDR3 RAM running at
500MHz. The GPU is cooled by a
second heat pipe.THERMAL UNIT AND HEAT PIPES
A PC in your kitchen should be
seen, not heard. The IQ770 oper-
ates with just two fans: One sits
above a very large heatsink. A set
of heat pipes wicks heat from the
CPU and GPU. The second fan cools
the diminutive power supply.TENSION SPRINGS
These large springs keep
the 19-inch touch screen at
the desired height.