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Parallel vs. Serial ATA

by Lucas Frawley

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Introduction

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
Hardware, Configurations & Pictures
Conclusion

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.

	Parallel ATA	Serial ATA
Maximum Speed	100 MB/s with bursts up to 133 MB/s	150 MB/s Currently 300 MB/s by 2005 and 600 MB/s by 2008
Cable Length	18 Inches	1 Meter (about 40 inches)
Cable Pins	40	7
Power Connector Pins	4	15
Data transfer wires used	26	2
Power Consumption	5V	250 mV
Hot Swappable?	No	Yes

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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, power adapters, 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 flexibility.

(Fig. 2) SATA is the undisputed champion in terms of size and flexibility of cables.

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 connection.

(Fig. 6) It�s quite easy to distinguish the winner here: SATA takes the gold without a doubt.

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Conclusion

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: | SATA Motherboards | SATA Controller and Adapter Cards | SATA Cables | SATA Power Adapters |

Other Articles by Lucas Frawley: | How to Build a Baybus | A Guide to Connecting Wires |

This information has been provided as a reference. Directron.com is not responsible for any problem as a result of properly or improperly following the advice above.

Last Updated: 6/24/03

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