If you've been in the market for a new computer lately, or perhaps just looked at an upgrade to your motherboard, you may have noticed that the new motherboards offer SATA as well as ATA connections for hard drives.
What are SATA drives and are they worth a look?
Let’s start with a little history on the name. The hard drives that have typically been in all PC’s for the last twenty or so years are referred to as ATA (Advanced Technology Attachment) drives. Advanced Technology Attachment is actually a standard which defines how data is transferred between the hard drive and the mother board inside your computer (this is independent of how quickly the hard drive itself can obtain data from the disk). If you’ve ever looked inside your computer you may know that the hard drive connects to the mother board via a ribbon cable. This ribbon cable has forty separate wires in it that are used to transfer the data. Sixteen of the wires are used for the actual data while the other twenty-four are used for various signaling and power requirements. ATA drives transfer data sixteen pieces (or bits) at a time which is referred to as a “parallel” transfer. (Since eight bits are referred to as a byte, sixteen bits is the equivalent of two bytes.) Today, these types of ATA style drives are referred to as PATA or Parallel ATA to designate that they transfer data several bits at a time.
Now along comes SATA which stands for Serial ATA. Serial implies that the data is transferred one bit at a time. So then the logical question becomes: how can a drive that transfers data one bit at a time be as fast, or faster, than a drive that transfers data sixteen bits (two bytes) at a time.
The main reason has to do with the electrical constraints associated with transferring data across wires that are so close to each other. This proximity can cause problems such as crosstalk and ringing. There is also the settle time that is required, which means each transmission has to wait until all the lines are stable and ready to go before the data is sent. For these and other reasons beyond the scope of this article, the maximum transfer rate for the latest version of the PATA interface (ATA/ATAPI-7) is 133 Mbytes/sec. Also beyond the scope of this article are the reasons why SATA can perform so much faster; but in its simplest form, it is because data is continuously sent over the cable (even when nothing is being requested from the hard drive – this keeps the timing between the sender and receiver in synch) so none of the PATA constraints have to be dealt with. The data is continuously streaming at much higher rates than can be achieved over the parallel ribbon cable.
PATA devices have gone through several upgrades over the years to increase the speed of the interface to keep up with faster hard drives. Due to the difficulties in getting PATA speeds up past 133 Mbytes/s, SATA was developed as the future interface in anticipation of faster and faster hard drives.
The first version of SATA was SATA/150 or SATA 1. This had a 1.5 gigabit per second (Gbit/s) transfer rate. After overhead is accounted for, the actual rate is approximately 1.2 Gbits/s which is the equivalent of 1,200 megabits per second (Mb/s). 1,200 Mb/s converts to 150 megabytes per second (dividing by 8 since there are 8 bits in a byte). So while SATA 1 was faster at 150 megabytes per second (MB/s – upper case B), it was only 17 MB/s faster than PATA. Not a blazing speed increase.
Subsequently SATA 3.0 was introduced with a speed of 3.0 Gbit/sec. And SATA 6.0 is on in the future plan (with a transfer rate of 6.0 Gbit/sec).
So is SATA the better choice? Although it is capable of transferring data faster, most hard drives today can only move data from the drive to the cable at a maximum rate of about 120 MB/s. So until hard drives can supply the data to the SATA interface faster, the extra bandwidth of the SATA cabling will go unused.
Some more obvious advantages of SATA are: the interface supports ‘hot swapping;’ maximum cable length of 39” is more than double the PATA interface spec of 18”; the SATA cable has seven conductors as opposed to forty for PATA so it is easier to route and handle; and the SATA cable is cheaper.However, the ‘hot swapping’ feature - as well as a few others - are only supported when there is operating system support for the SATA standard interface (AHCI, or Advanced Host Controller Interface). Due to the relative newness of this technology, this standard is only supported by new operating systems (Windows Vista, Mac OS X, and Linux). XP and older MAC OS’s do not have this support. You can still run the SATA drive on these systems (in what is referred to as “IDE Simulation Mode”), you just won’t have the hot swap and other features which are enabled by the standard.
Another important item that I don’t want to forget to mention is that you’ll obviously need something to plug your SATA hard drive cable into. Either you have a fairly new motherboard which already has SATA connectors on it, or you have an older mother board which doesn’t. If it’s the latter, you’d then have to incur the added cost of buying a SATA add-on card to plug into one of your mother board’s expansion slots.
So if you’re looking for a new or additional hard drive, my advice is:
- If your mother board has SATA connectors on it, go with the best price hard drive you can get. Either SATA or PATA will do the job.
- If your mother board does not have SATA connectors, buy a PATA drive. The added cost of the add-on card will make the SATA drive more expensive.
- Or, if you’re just one of those people who always wants the latest and greatest, go with the SATA drive.
Just for comparison, here are some other interface transfer rates (all in MB/s):
USB 2.0 60
FireWire 800 98.25
PATA 133 133
SATA 150 187.5
SATA 300 375
Also, Fiber Optic cables can transfer data at up to 2,000 MB/s.
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