Overview
Serial ATA, or SATA, is a relatively new storage technology that is
now being adopted in computers. It is the successor to Parallel ATA.
SATA allows for faster transfers between the hard disk and the system,
uses thinner cables and is easier to physically install.
The Technology
ATA stands for AT Attachment. ATAPI - a term that will be well used
in this article - stands for ATA Packet Interface. AT is the designation
used by IBM for their early range of personal computers. ATA/ATAPI
is the single most popular interface for disk drives, the alternative
method being SCSI, which is found where speed and reliability are
essential. SCSI is not used by the vast majority of users due to
cost.
Most USB pendrives, flash memory cards, CDROM drives and PCMCIA
devices are also based on the ATA/ATAPI standard. These standards
are developed and maintained by a governing body named INCITS –
InterNational Committee for Information Technology Standards.
The ATA standard was developed in 1986 when a trio of companies
(Western Digital, CDC subdivision Imprimis and Compaq) were manufacturing
disk drives. At that time WD was a major manufacturer of silicon
chips, having developed and produced the hard drive controller chips
for the IBM PC/AT machines during 1984.
Compaq were the first to start using 3.5” drives fitted with
the new interface manufactured by Connor Peripherals. The interface
only started to take off when other distributors started using the
drives and they started to become available in retail outlets. Since
then the original specification has been improved upon and refined
leading to several types of ATA standard, from ATA-1 offering 16.6MiB/s,
up to and including ATA-7 used by some manufacturers providing 133MiB/s
in burst mode which is the most recent version.
Serial ATA is the next evolutionary stage in the development of
magnetic storage media, it differs from PATA not only in the speeds
attainable (150MiB/s to 600MiB/s as opposed to a maximum of 133MiB/s
burst speed with PATA), but in the physical layout of the connector
and other hardware.
The most glaring difference should the two connectors be placed
next to each other is the size, PATA cables are 20 pins wide in
two layers giving 40 pins, whereas the SATA connector is a mere
7 pins wide in a single layer. One advantage of this is the ease
with which SATA cables can be run through your case. PATA ribbon
cables take up a lot of space and can block airflow through the
case. PATA cables are also length limited by signal attenuation
making the maximum useable length of the cable around 45cm. SATA
cables can be up to a meter long before the signal degrades. One
potential disadvantage with these new connectors is the increased
risk of damage to the less robust pins. The power connector also
differs from the standard molex, though adaptors are readily available
for those who own power supplies without the correct connector for
SATA devices.
The major advantage that SATA has over PATA is the way in which
data is transferred. PATA cables use bidirectional channels for
data, the channels able to transmit data both to and from the controller,
SATA uses a different method with a pair of separate channels for
data lines with this method reducing crosstalk and other types of
impedance. SATA drives use a low voltage swing method of transferring
data with a voltage differential of 0.125V, whereas PATA devices
use a 3.3V signalling method. This low voltage swing greatly improves
the energy efficiency of the device decreasing drain on the PSU
and decreasing the heat output of the system as a whole; important
for those large RAID arrays and allows greater speeds to be attained
as signal integrity is maintained.
