Thursday, June 9, 2011

PATA vs. SATA

Computer components and devices are so heavily intertwined that it is hard to separate entries into very basic topics so that beginners can understand what I am talking about. I consider this entry 3 of 3 of what was initially just going to be one entry- HDD vs. SSD. That didn’t work out so well, but at least it gives me more stuff to write about.

This entry is about computer component interfaces. When I was first starting to learn about the inside of computers, this section took me a while to understand  but all it is just how computers components connect to one another and how information travels to each component. There are different types of interfaces that were used more in the past (SCSI, Firewire, Centronics), but the two I will be focusing on are PATA and SATA.

Though it is not as popular as it once was, expect to work with PATA on older computers. PATA stands for Parallel AT Attachment, and is the name given retroactively to devices that transmit data over parallel (Wikipedia, 2011). It is just easier to assign the one name, because PATA has been called by different names over the years (IDE is the most common, but EIDE, ATA, ATAPI exist out there too. It’s all PATA now). PATA transmits data 8 bits over 8 transmittal wires (one bit per wire= 1 byte) through a 40 pin ribbon cable that can connect up to two drives inside the computer.

SATA stands for Serial Advanced Technology Attachment, and this bus interface is an improvement on PATA in many different ways. Unlike PATA, SATA can only connect to one drive, but in return it provides higher data transfer, reduced bulk (those ribbon cables are huge!), and it’s hot swappable! An example of a common use of SATA transfer is the USB flash drives that are like a mini portable hard drive. I remember those little devices becoming popular when I was in college; a godsend since I didn’t have to carry floppy disks or those giant Iomega disks around with me anymore. SATA transmits data one bit a time in a single stream. The PATA interfaces can transmit data at speeds between 5 MB per second to 133 MB per second; SATA transmits much faster, at rates between 150 MB per second to 300 MB per second (Blogulate, 2007).

So why does SATA transmit data faster than PATA? This took me a while to understand because one would think that with 8 bits going over a wire at once, that would mean information would be sending faster than in one single stream. Here are the reasons why this isn’t the case:

1.      Those 8 bits traveling the wires may not reach the destination all at once. The computer will start to slow down when it has to wait for all those bits to catch up (Blogulate, 2007).
2.       The more wires (This vs. this) there are, the higher the chance there is for disturbances (Blogulate, 2007).
3.       Those 8 bits have to convert back into one stream in order for the destination port to read them, and this adds time. Since serial is already being transmitted in one single stream, no conversion needs to happen, and time is saved (Wikipedia, 2011).

PATA and SATA are not interchangeable, so any devices will have to be one or the other, unless there is an adapter.

Blogulate. (2007, December 2). Why is Serial communication preferred over Parallel ? Retrieved June 8, 2011, from Blogulate: http://blogulate.com/content/why-is-serial-communication-preferred-over-parallel/
Wikipedia. (2011, May 31). Parallel ATA. Retrieved June 9, 2011, from Wikipedia: http://en.wikipedia.org/wiki/Parallel_ATA
Wikipedia. (2011, June 4). Serial ATA. Retrieved June 9, 2011, from Wikipedia: http://en.wikipedia.org/wiki/SATA

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