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| FastSilicon's Guide To Storage Technology: Part 1 |
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Page 2 of 4 SATA (Serial ATA) Ahh yes. Serial ATA. The evolutionary step from IDE/EIDE mass storage devices. Serial ATA storage devices are in a league of their own. Not only are they completely different than IDE/EIDE devices, they also have quite a few interesting features worth mentioning. With evolution comes perfection, however, this cannot be said about Serial ATA technology.  First off, lets
hit the performance aspect. When it comes down to it, Serial ATA is
just plain quick. No matter the task, no matter the load, the
technology seems to be able to handle it pretty well. Got a database
server with lots of heavy database queries and data being constantly
written to? Serial ATA may be for you. Do you play demanding games?
Serial ATA technology is quick, and can (under ideal situations)
improve your game load times at least 50% over IDE/EIDE. Having said
that, there are still many Serial ATA drives that aren't all that
much faster than their older IDE/EIDE brethren. The specification
allows for a 30-40% performance improvement in comparison to a
similarly equipped EIDE disk but its the lack of proper
implementation that kills the main goal of serial transfer
technology. This is primarily a matter of cost, as Serial ATA has
replaced IDE/EIDE as the main storage system used in desktop and
mobile PC's.
Spindle speed again is one of those things that affect drive performance. The spindle of a high end Serial ATA desktop drive runs at a considerably higher speed than a high performance IDE/EIDE disk. 10,000 rpm. Yup, you heard it. It spins as fast as a dremel! Not that Dremel tools and hard disk spindles have anything to do with each other. I was simply making the point that perhaps if you touch the edge of the spinning platter to a piece of wood it might cut a notch in it! Back to a more serious note though. The 10,000 RPM platter rotation speed is what gives Serial ATA its edge over the IDE disks of old.  Well, hooray for
performance. Performance isnt everything though :) Lets talk about
storage capacity and price, shall we? From a pocketbook standpoint,
Serial ATA wont put too much of a hurt on you, unless you really need
a lot of storage space. With disk drives ranging from 80GB all the
way up to 750GB, and soon 800GB, there are many options. 160 and
250GB disks are the most commonly sold, and range from $60 to $100,
depending on features and specifications. As you can see, they are a
tad more expensive than IDE storage, but the price is worth it if you
are seeking performance gains.The last two features I am going to touch on before I move on to my favorite mass storage device type is Serial ATA's increased buffer and the use of a new technology called Native Command Queuing. First off, the buffer in most Serial ATA disks is 16MB, a 100% increase over EIDE's 8MB of on disk cache. This enables the drive to store more data in its on board memory units that is going through the interface. This improves read/write performance tremendously. Why you ask? Because if the data is sitting in a high speed bucket (the cache/buffer), it can be sent instantly to the interface for transport over the system bus, or be sent directly to the write head for writing back to the disk. Why is this such a fast improvement? Well, if data is already in the buffer, the read heads dont have to seek on the platters and read data. Or the CPU doesn't have to fetch data from your system RAM and send it to the disk. It's already there! Nifty huh? Buffer size drastically affects overall disk throughput. A simple test to check this is to run a buffered read test on a 2MB cache, 8MB cache, and a 16MB cache drive. You can just guess which will have the highest throughput :) Nah I'll just tell you. The disk drive with a 10,000 rpm spindle and a 16MB cache will blow the others away. Serial ATA has a buffered disk read of about 100MB/s continously. Compared to the IDE/EIDE's 2MB disks @ about 40MB/s, and the top end with an 8MB cache reaching about 60MB/s, Serial ATA is THE option if you need a high performance disk w/o paying too much money.  Now onto that
weird term I mentioned up there. I saw your face, it was all twisted
like WHA!?? Is this guy on crack? No I assure you I am not smoking
any illegal substances. Serial ATA has a new feature in revision II
(Sata 2) that is called Native Command Queueing. Simply put, this
allows the drive to do 2 things. First, the controller can be sent
multiple commands at once from the system. This allows the drive to
take orders while performing operations, instead of telling the
system to wait. Second, it can perform a simple checklist of the
tasks it is currently doing, compare the tasks, and orders them in
the best possible way to get the maximum amount of performance. This
allows the disk to process a very large amount of transactions and do
them as efficiently as it can, and the result is a smoother and
faster disk subsystem. Hooray for NCQ huh? Well not really. It does
have its nasty sore thumb. If the command queue gets too deep, the
drive will, however very rarely, completely ignore any more incoming
commands from the system until it has emptied the queue and completed
its tasks. This has the obvious downside of a drastic system
performance drop. All in all, however, SATA is a great technology.
And of course, its also not as expensive as the next type of mass
storage, which is geared towards being the untouchable king of
performance.
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