Serial ATA

Serial ATA

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There have been some components of PCs that haven’t changed much since the early days of PC’s, nearly 15 years ago. Floppy drives are still around, and haven’t changed since the standard became the high-density 3.5″ disk many, many years ago. Slowly but surely, the aging old floppies are slowly becoming redundant, with the extra push from Intel to go to a legacy free PC standard.

Another of the oldest standards is the IDE ribbon cable for hard drives. Besides the slight increase in data speeds, not much has really changed for the IDE cable, with the only physical change being the extra grounding wires for the ATA66 and above standards. They are still quite a clumsy cable, although this is has been slightly corrected since rounded IDE cables became popular.

When most people think “serial”, the most common association is with the serial ports within a PC. These are of course very slow, but synchronous serial (as opposed to the asynchronous RS232 PC standard) offers much higher data throughput. In comparison, a typical PC serial port is capable of 115kb/s, whereas Serial ATA is capable of over 1,000,000kb/s!

Finally, Serial ATA offers us a much better cabling system for hard drives, with faster speeds and a better data transfer interface. It also introduces a few other changes (that are outlined below), but I think the biggest difference that will be noticed is the physical aspect of the cable.

What is different?

Parallel ATA vs Serial ATA cabling

The first obvious difference with Serial ATA is the cable. No 40 pin connectors, no messy ribbon cable, but instead a small 7 pin connector, and a cable that’s only just thicker than a cable you would find on a keyboard or mouse. This is going to be beneficial to keeping a neater case, and will certainly make a difference for PC’s like the Shuttle Barebones systems.

The new connectors

As the name suggests, the data will be transmitted in serial format, unlike it’s predecessor (IDE ribbon cable) which relies on the parallel data format. This is what makes the cable itself only need seven wires, as serial essentially only has 1 send and 1 receive channel. The seven wires consist of a differential pair for both transmit and receive, as well as 3 grounds. The introduction of a differential signal means that less grounding is needed, and greater resistance to electrical interference.

We will see a greater speed available from the Serial ATA standard, with the initial implementation capable of 150mb/s.By the end of 2003, it’s predicted that we will be seeing Serial ATA hit over 300mb/s. Of course, the real benefit of the faster interface speeds may not translate to much in the real world. Even the fastest hard drives cannot sustain much more than 40mb/s, so only cache hits will be able to use the full 150mb/s. As hard drives advance, we can hopefully start to see them utilising more and more of the capable bandwidth.

The new standard is also backwards compatible, so it’ll be easy to convert from Serial to Parallel formats, and vice versa. Products like the HighPoint RocketHead will allow normal, parallel ATA drives to run on a Serial ATA controller. This should hopefully increase the adoption rate of Serial ATA, and we’ll all be able to enjoy the benefits sooner.

HighPoint RocketHead 100

Signal voltages on the data lines have been lowered from 5 volts, to a mere 0.7 volts. This will allow the drives to have a lower power handling, as well as reduce the size of the controller. Serial ATA will also have a greater error correction capability, with the largest difference being that the instructions (not just the data itself) will now be checked for errors. This should result in higher reliability, and less chance of data corruption.

Who is making Serial ATA products?

If you have seen any of the pictures from Computex this year, most motherboard manufacturers have already begun integrating Serial ATA controllers into their hardware. Most of the latest motherboards just coming out will feature Serial ATA capabilities, and I’m sure it won’t be long until it’s a standard feature across most motherboards.

Standards like USB have taken a while to fully take off when it was first introduced, but you’d be hard pressed to find any new PC or motherboard without at least 2 USB ports. The availability of USB devices now has skyrocketed, and the latest change to USB 2.0 has gained support much quicker. Like USB, Serial ATA drives will also be hot swappable, which should allow for greater flexability.

The Seagate Barracuda V, available soon

All of the major hard drive manufacturers have been busy developing Serial ATA drives, which is already a good sign. Some manufacturers may have gone for a simple solution of bridging the current controller to work with Serial ATA, but others (such as Seagate) have completely redesigned their onboard controllers to talk directly in serial mode. Complete integration should hopefully allow the drives to make full use of the Serial ATA interface.

RocketRAID 1520 2-Channel Serial ATA RAID controller

Companies like Highpoint have also released a Serial ATA RAID controller, which is where I believe Serial ATA will start to become very interesting. IDE drives are continuing to progress in speed and capacity, and we are starting to see quite cost effective use if these drives in basic RAID configurations. Serial ATA will bring the benefits of greater data integrity, increased speed and some of the extra commands should be very beneficial to RAID setups.


It’s obvious that Serial ATA is going to introduce some much needed changes to the way IDE data is transported, but it may take a while until we see the benefits of these changes. The uptake of the new technology will certainly be dictated by the availability of the controllers (both on motherboards and PCI controllers), the availability hardware of the hardware (hard drives, CDROMS etc) and most importantly the price.

The initial implementation of any new technology can be tricky at the best of times, but hopefully the manufacturers will have done their homework properly. While PC enthusiasts love to tinker and test new technology, the business and corporate buyers will be less likely to invest in anything “unproven”.

We should start to see the first generation of Serial ATA drives released before the end of this year, and motherboards with Serial ATA are already on the market. Hopefully we can expect to see some smaller performance gains, with speeds ramping up for the 2nd and 3rd generation Serial ATA devices. Serial ATA is here now for the next 10 or so years, and I’ll certainly be glad to finally rid my system of IDE cables.

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