Serial in the box ..................................................................................
Serial ATA represents another step away from parallel wiring for high-speed
communication. First I tell you why the techies are all excited, and then I tell
you how it won’t make much of a difference to you as a laptop user except
that you’ll have to make sure you know what you’re buying when it comes
time to upgrade a hard drive.To this point in the history of the PC, nearly every hard drive has used paral-
lel ATA as the transfer protocol for data. (A relatively small number of drives,
mostly used in high-demand graphics or as servers, used high-speed SCSI
serial interfaces.)One significant disadvantage of parallel ATA was the fact that the motherboard
and the drive had to be connected by a wide and unwieldy 40- or 80-wire
cable and a 40-pin connector. Another problem was the requirement that
26 of the wires carry 5-volt signals.Among the beauties of serial ATA is the fact this standard requires only four thin
wires in a casing similar to a telephone cable. The first specification for SATA
requires only four 500 millivolt (^1 ⁄ 2 volt) signals; future versions are expected
to allow use of signal voltages half again as strong at 250 millivolts or^1 ⁄ 4 volt.As a laptop user, you’re not likely to be working under the covers of your
machine moving cables and worrying about the proper flow of cooling —
both problems that exist for designers and upgraders of desktop and tower
PCs. But you will benefit when future motherboards use SATA because
designs will become simpler, electrical demands a bit less, and throughput of
data improved. The first drives and adapters offer only a tiny increase in true
throughput — perhaps 1–5 percent — compared to parallel ATA, but future
specifications are expected to double and triple throughput to 300 MBps
and 600 MBps.Serial ATAis a point-to-point interface with each device directly connected to
the motherboard and able to use the entire bandwidth; parallel ATAtypically
uses a master and slave arrangement for pairs of devices, and in certain circum-
stances the two drives may have to share the same channel for loading or
unloading data. And serial ATA is also capable of being set up to be hot pluggable
(like USB and certain PC Card devices), allowing drives to be attached or
removed from a laptop while it is running. The politically incorrect terms of
masterand slaverefer to the fact that one device on the connector is considered
to be the dominant piece of equipment, with the slave subservient to it or with a
lower priority when it comes to demanding the attention of the microprocessor.All that said, serial ATA drives have not yet arrived in consumer laptop
designs. When they do, you’ll have to take care to distinguish between plug-in
hard drives (and CD and DVD devices) that expect a parallel connection and
those that are looking for a serial attachment.122 Part III: Laying Hands on the Major Parts