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Untitled Document
Serial ATA
The SATA standard is the first time in nearly 20 years that any major changes
have occurred in hard drive technology, beyond exponentially increasing drive
capacities and incremental improvements to the IDE standard.
Despite the ever increasing pace of technological development, the upgradeable
nature of the PC means that old technology can take decades to die, since people
always want backwards compatibility. The IDE standard has been with us for as
long as the 1.44 megabyte floppy disk, or the scroll lock key. Unlike the scroll
lock key, the IDE hard drive is still very useful, but eventually any technology
must reach its limits. This is where SATA comes in.
SATA, or Serial ATA, is quite a departure from the older Parallel ATA designs.
The Parallel ATA standard transmits 16 bits at once (i.e. in parallel), but
SATA uses a serial data transfer method, sending one bit at a time in a constant
stream. The ribbon cable of the Parallel ATA drive has proven to be its downfall,
as interference between the many wires limits the amount of data you can transfer
without an unacceptable error rate. For a time, this was cured by the introduction
of 80 core cables, which use the extra wires as earthing to reduce the interference.
Although SATA transmits less data per clock cycle, the simpler electrical design
allows for much higher clock speeds and therefore greather bandwidth. The current
SATA spec gives a bandwidth of 150MB/s, which doesn’t seem like a huge
improvement over 133MB/s ATA. SATA is here to stay though, and is likely to
be the standard PC drive interface for the next 10 years. Like Parallel ATA,
Serial ATA will undoubtedly have occasional upgrades, all backwards compatible
of course. It is expected that SATA technology will eventually reach up to 6
GB/s before running out of steam.
As the fashion for rounded IDE cables has shown, people are losing patience
with bulky and messy ribbon cables. SATA has reduced the data wiring to a single
slim wire, with small and easy to use connectors. This is just a fringe benefit
of SATA, but it makes a RAID installation much easier and tidier.
From left to right, we see the IDE ribbon cable, SATA connector and SATA power
connector.
SATA has also brought with it a new power connector. This connector probably
has you wondering what was wrong with the old one, especially with most people
using molex adapters. The new power connector makes more sense when you consider
the SATA standard is planned to last for 10 years or more. The connector brings
a 3.3 volt supply to the drive. This isn't used for anything yet, but in the
future, this 3.3 volt supply will be useful for running the low power electronics
on the drive, keeping costs down.
The new power connector, like the data connector, has no latching mechanism
and is very easy to push in and out. This is because the SATA standard has been
designed with hot swapping and external drives in mind.
Parallel ATA is by no means dead yet as it still the predominant standard for
optical drives and most of the latest hard drives come in both SATA and PATA varieties.
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