Friday, March 14, 2014

What Makes Solid State Drives (SSD's) Different from Traditional Hard Disk Drives

Lately it is hard to hear about disk drives for a computer, laptop, server, or other device, without hearing about solid state drives (SSD's).  Most people have heard of SSD's at least once, whether they fully understand how they work, know if they could benefit from them, or what all the fuss is.  Listed below are some of the ways SSD's are different from traditional hard disk drives (HDD's).

How they work in a nutshell
Traditional hard drives have a set of stacked platters that spin to provide access to your data as a mechanical arm moves between these platters.  The mechanical arm reads data from the platters and writes data to the platters using a magnetic charge.  HDD's write new data into the next available sectors, leaving existing data where it originally was read from whenever possible.

SSD's do not have any mechanical parts,meaning there are no spinning platters so they run much quieter than HDD's.  Instead of spinning platters, SSD's operate similar to the memory in your computer.  The RAM in your computer is volatile memory, meaning it holds data until the power is turned off to it at which point all items stored there are lost.  Think about a time when you were working on a project and your computer suddenly froze.  In that situation, it is likely you lost everything you had done to that file you had open since your last save or auto-save.  These changes are lost because the changes sat in memory waiting to be saved, or written to disk, when the computer froze.  Once the computer froze, the changes were lost from RAM, unable to be retrieved upon reboot.  SSD's on the other hand, use non-volatile memory, called flash memory, so data stored there remains even when the power is turned off.

Physical Size
SSD's are smaller than HDD's making them perfect for laptops, ultrabooks, and tablets.  SSD's can also be used in traditional desktop computers fairly easily as many ship with the components needed to fit compatibly inside a desktop computer tower.  If you purchase a SSD that does not ship with these adaptive components, you can find them available online from many electronics companies.  Most of the adaptive cases can be reused between multiple desktop cases.

As with any new technology, SSD's are more expensive than HDD's because the technology used is different.  Instead of stacked platters, a SSD uses a type of flash memory comprised of transistors.  While prices continue to come down on SSD's, you will find different brands are priced differently as with any product.  When browsing for a SSD, keep in mind the price will often get cheaper per GB the larger the size of the drive.  However, purchasing a 500GB SSD for $429, when you only need 100GB, and can purchase a 250GB SSD for $249 might not really be a deal for you.  

Before purchasing a new SSD or HDD, take a look at how much disk space you actually need by checking what you are currently using.  If you right click on the hard drive (C:), you can see how much of your existing disk space is currently being used.  Also, right click on your files, often stored in the My Documents folder on a Windows machine, to see how much of the total disk usage is your data versus the operating system and application files.  Knowing how much of the disk space is being used by your data can help you predict how much disk space you will need for regular growth over the life of the drive.  

Lastly, consider what types of files you store.  Documents take up much less space than videos and music, even if you create new documents often.  If you find yourself adding music and photos every week, the space you will need for growth over the life of the drive will be much higher.  Ultimately, the appropriate size drive for you will depend on what data you store on it and how you plan to use it in the future.

SSD's are known for their increased levels of speed compared to HDD's.  Remember how we described HDD's, a set of stacked platters with a mechanical arm moving back and forth between them reading or writing data.  As new data is written on a HDD, it is written to the next available sector.  So, if a file you created last month was changed each week for four weeks, that one file could potentially be broken out and stored in five different sectors spanned across the stacked platters.  This means the mechanical arm must switch between each of those sectors to grab all the data belonging to that particular file.  Since SSD's do not have mechanical parts, the time it takes to access each file is the same because access time is not relative to the location of the last file accessed.  Without mechanical arms moving between platters, the time it takes to access files is much quicker than HDD's.

This difference in storing, and therefore accessing, data is what allows devices with SSD's to boot up in about half the time of a HDD on average.  There are other important things to note about the differences in speed between SSD's and HDD's.  For instance, while the example above shows the read speeds between SSD's and HDD's are substantially different, the write speeds do not have as big a gap.  SSD's do provide faster write speeds than HDD's in most cases, but the difference factor is much less than the difference factor in the read speeds which have been reported to be as much as ten times faster.  Remember though, like any computer part, your results will vary based on your unique setup.

There are valid concerns about the longevity of SSD's yet there are tests that have shown SSD's will last longer than they are warrantied by the manufacturer.  As will all things tech, you will find arguments for both sides and both can be valid for different situations.  So what does that mean for you?  Well, one thing to note is SSD's write data differently than HDD's.  While HDD's write data to the next available empty block in a sector, SSD's are broken into cells of data and must erase an entire cell to be able to write new data to that cell.  Additionally, many SSD manufacturer warranties cover the SSD up to a certain number of writes to cells rather than a number of years because the age measurement for a SSD is more accurately measured this way.  SSD's have a limited number of write cycles and once that amount is hit, the drive is no longer under warranty, regardless of how quickly that number of cycles hits.  Like any warranty, just because the number of writes or number of years runs out does not mean the drive is dead.

Ultimately, the number of cycles for each cell is based on how you use your device.  Also to note, some SSD manufacturers use wear-leveling.  Wear-leveling extends the overall life of SSD's by moving "static", or rarely changed, data to different cells to keep the wear pattern on each cell as consistent as possible.  Purchasing a SSD that utilizes wear-leveling should provide a drive with increased longevity over one without this feature.

In summary, just because SSD's are the newest technology does not necessarily mean they are the right solution for everyone.  Use the above factors, as well as reviews of specific drive models when you are purchasing your next drive.  Rarely is there any one type or model of a product that can meet the needs of everyone best, because that does not take into account each individual's particular needs and uses.  

Whatever type of drive you choose, consider all aspects of your purchase so you get the best solution for your existing and future needs.

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