Parallel vs. Serial ATA
by Lucas Frawley
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If someone were to say they preferred a serial connection to a parallel connection, most would laugh
at them uncontrollably. Serial COM ports have always been known to be one of the slowest connections
in modern computers. However, the newest version of Advanced Technology Attachment (ATA), Serial
ATA, is set to sweep parallel ATA off its feet.
PATA vs. SATA
Parallel ATA (PATA) has been the industry standard for connecting hard drives and other devices in
computers for well over a decade. However, due to a few major limitations, PATA could be a quickly
dying breed with the introduction of Serial ATA (SATA). To compare, PATA cables are limited to only
18 inches long, while SATA cables can be up to 1 meter in length, which is less than 40 inches.
It is possible to have longer cables but, due to attenuation, these longer cables are generally more
trouble than they are worth.
PATA cables are large and bulky and can easily restrict airflow. With the onslaught of
better and faster devices, computers continue to generate more heat and this can cause many problems
including complete computer failure. PATA cables are 40 wires wide and they block precious space,
which can restrict airflow greatly. SATA cables are only 7 pins wide and, with their longer maximum
length, can be easily routed to not restrict any airflow at all. The change to serial transfer is
what allows the cable to be so thin, only two data channels are required, one for sending and one
for receiving data. Parallel cables use multiple wires for both sending and receiving and this
technology uses a total of 26 wires for data transfer.
Another comparison is that SATA devices require much less power than PATA. Chip core
voltages continue to decline and, because of this, PATA's 5-volt requirement is increasingly
difficult to meet. In contrast, SATA only requires 250 mV to effectively operate. SATA is
also hot-swappable meaning that devices can be added or removed while the computer is on (depends on OS features to detect new hardware after hot-swap).
The last, and most important, difference is the maximum bandwidth between the two technologies.
The true maximum transfer rate of PATA is 100 MB/sec with bursts up to 133 MB/sec. With the first
introduction of SATA, the maximum transfer rate is 150 MB/sec. This is supposed to increase every
3 years with a maximum transfer of 300 MB/sec in 2005 and 600 MB/sec in 2008. Finally, SATA doesn't
require any changes to existing operating systems for implementation. SATA is 100% software
compatible and, with SATA adapters, some hardware doesn't have to be immediately replaced.
MB/s with bursts up to 133 MB/s
MB/s Currently 300 MB/s by 2005 and 600 MB/s by 2008
(about 40 inches)
Power Connector Pins
Data transfer wires used
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Hardware, Configurations & Pictures
Between the last quarter of 2002 and the first quarter of 2003, motherboards with
onboard SATA adapters were released to the public market. For users that are
not ready to purchase new motherboards, SATA RAID
controllers are available as
well. Most Hard drive manufacturers released their first
SATA hard drives for sale in the first or second quarter of 2003. For those that would
like to take advantage of SATA's longer and thinner cabling requirements without
having to purchase new hard drives,
SATA adapters, can
be purchased to convert current drives to accept SATA cables. To fully
implement the SATA standard a new motherboard, a new hard drive or other storage
device and a new power supply or power adapter must be purchased. Its unknown
how soon power supplies with new SATA power connectors will be available for
sale but, for the time being,
can be used with existing power supplies.
When looking at the hardware for serial connections, one can easily see the
differences between it and parallel ATA. A side-by-side comparison of the two
connectors on a motherboard is shown in figure 1. As shown, the SATA connector
is much smaller than its parallel counterpart. This effectively means that
motherboard manufacturers will have more room to include more on board options
as well as being able to offer better board layouts, as this will not be so
restricted by the ATA connectors.
(Fig. 1) These pictures show the difference in size of PATA and SATA connectors.
Furthermore, a look at figure 2 shows a PATA cable on the left and an SATA
cable on the right.As is easily apparent, the SATA cable is much more builder
friendly and can be easily routed out of the way in a case due to its length and
(Fig. 2) SATA is the undisputed champion in terms of size and flexibility of
Figure 3 shows an SATA power adapter with a 15-pin connector as opposed to
the customary 4 pin connectors in parallel ATA. The new 15-pin connector may
sound as though it would be a hindrance in comparison to the older ones but the
two connectors measure almost the same width. The reason for the 15-pin
connector is so that different voltages are supplied to the appropriate places.
In addition to the customary 5v and 12v wires, new 3.3v wires are included for
the new devices. 9 of the pins provided are for the positive, negative and
ground contacts for each voltage. The remaining 6 connectors are for the
hot-swappable feature of SATA, designating an additional two contacts per
voltage for this.
(Fig. 3) As seen in the picture above, SATA power connectors are still the same
size as current power connectors even though they have a total of 15 contacts.
As discussed earlier in this article, SATA to PATA adapters are currently
available to allow existing hard drives to be used with new motherboards or
controller cards and one is shown below in figure 4.
The package, made by
Soyo, includes the SATA to PATA adapter, 1 SATA cable and a short
instructional manual. To connect this to a hard drive, simply connect the
40-pin PATA adapter to the connector on the drive as shown in figure 5. Also, 7
jumpers will have to be set according to the instructions shown in the manual.
Then, connect one end of the serial cable to the adapter and the other end to
a motherboard or controller card. Finally, connect a power connector to both
the hard drive and the SATA adapter. This device can be used to connect a PATA
drive to a SATA connector on a motherboard or controller card, connect a SATA
drive to a PATA connector on a motherboard or, with the use of two adapter kits,
connect a PATA drive to a PATA connector on a motherboard using an SATA cable. Figure 6 below shows a comparison of the inside of a computer case with a PATA
cable connected to a hard drive and a SATA cable connected to a hard drive.
(Fig. 5) Standard PATA cable
(Fig. 6) Itís quite easy to distinguish the winner here: SATA takes the gold
without a doubt.
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It is unknown how quickly most consumers will begin using Serial ATA devices. The majority of
current PC users will not want to trade in their existing system just to take
advantage of a few extra MB/s. However, many technical users and PC junkies may
find themselves huddled over their favorite suppliers?website waiting for the
instant the next set of SATA drives become available for sale. Furthermore, many
Original Equipment Manufacturers (OEMs) will look to incorporate SATA devices in
their PCs in the near future. The Parallel ATA interface is one of the few
aspects of a computer system that has remained unchanged for many years.
However, it appears PATA may be in search for its final resting spot once Serial
ATA begins to consume the retail market.
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Related Items: |
Controller and Adapter Cards |
Cables | SATA Power
Other Articles by Lucas Frawley: | How to Build a Baybus | A Guide to Connecting Wires |
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Last Updated: 6/24/03
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