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Solid State Disk vs. Spinning Hard Disk
  

Solid State Disk vs. Spinning Hard Disk

Until recently, all computers came with standard spinning hard drives.  These drives have been made for years and have become very inexpensive, even for capacities that far exceed what most people will ever need.  Recently, many computers have started having "hard drives" that are not spinning units but are "solid-state" in that they're made of silicon memory chips that have no moving parts.

What's the Difference?

A spinning hard drive is called "spinning" because there is a platter, not unlike what you'd see on an old record player, that spins very fast (typically 5400 or 7200 RPM).  This platter is coated with a magnetic material like what you'd find on a cassette tape.  Information is read and written to the platter via a very small, floating magnetic read/write head that literally "flies" microscopically above the platter.  Exactly like the way the wing on your plane uses the Bernoulli effect when in ground effect to float above the ground, the read/write head uses a cushion of air to stay above the platter.  These drives read faster than they write but generally do both fairly well.  Substantial electricity is required to keep the platter spinning.  This drains batteries and generates heat.

A solid-state drive (SSD) uses memory chips similar (but faster) to the ones you have in the memory cards that fit into your digital cameras, MP3 players and USB memory sticks.  There are no moving parts and no significant heat is generated.  They also only draw power when reading or writing data, not while just being "on."  They read data much faster than most spinning hard drives but write data more slowly.  They also cost more than spinning drives for the same capacity and, as of this writing, have a maximum capacity much smaller than the 250 GB spinning drive on the SkyPad2.

Are All Solid-State Drives the Same?

No.  They vary considerably in terms of both capacity and read vs. write speeds.  For the SkyPad2, we've selected 64 GB drives that are extremely fast in terms of both read (> 200 mb/s) and write (> 150 Mbs) speed.  Both are important although, for the SkyPad2, the read speed is more important.  By way of comparison, the original SkyPad had the fastest high-quality drive available for its unusual hard disk form-factor.  The SSD in the new SkyPad2 is nearly 3x faster and 2x the size.

So Do I Need a Solid State Drive?

You may not, which is why it's just an option for the SkyPad2.  The key issue is the fact that spinning drives have a read/write head that floats on a cushion of air.  As pilots, we know what happens to air density as the altitude increases in an unpressurized plane.  As the air density decreases, the read/write head gets closer and closer to the rapidly spinning disk platter.  At some point, typically at a pressure altitude of about 12,000 - 14,000 ft MSL, the read/write head slams into the disk platter, heavily damaging or even destroying it because of the extremely fast rotation (again, 5400 or 7200 RPM) rate.  Most hard disk manufactures limit their warranty to 10,000 ft.

A solid state drive (SSD), by contrast, doesn't rely on a cushion of air and isn't subject to significant altitude restrictions.  It also uses less power (increasing battery life), reads data much faster (the SkyPad spends most of its time reading, not writing, data), and runs cooler.

Therefore, if you routinely fly above 12,000 ft (unpressurized), you absolutely need an SSD.  If you fly below that or in a pressurized plane, the SSD is an option to consider if you want a unit with better performance and better battery life but it isn't necessary.

But is 64 GB Big Enough?

As of this writing, we sell 64 GB solid-state drives that use the fastest read/write speed available for consumer devices.  Unless you plan to put your iTunes library or all the photos you've ever taken of your children on the device, 64 GB is large enough (the original SkyPad had a 32 GB drive and it was large enough for most people).  As delivered, the SkyPad2, with Windows 7 itself, Voyager and all data (including all 14,700+ approach plates, all Sectionals, all IFR Low Altitude and IFR High Altitude charts) consumes just over 19 GB of space on the drive.  This leaves plenty of room for installing Microsoft Office or most other applications.  You can also free up some of this space if you need to in a few ways:

  • The SkyPad2 has a slot for an SD/HC memory card.  You can move the scanned charts (about 8 GB) from the internal drive to an SD memory card.
  • The SkyPad2 has two USB connectors.  You can use them to add an inexpensive external hard drive for times when you need to store massive amounts of information.
  • We configure the SkyPad2 to allow for a Windows feature called Hibernation.  This takes 2 GB of space on the drive that can be restored if you don't need this feature.  Hibernation, as the name might imply, is a long-term version of a laptop Sleep.  In Sleep mode, a laptop or tablet uses a small amount of power to keep the RAM active, allowing for extremely fast return from sleep to exactly where you left off.  With Hibernate, no power at all is used because the computer's memory is copied to the disk drive rather than retained "live" in RAM.  Thus, resuming from Hibernate takes much longer than resuming from Sleep because Windows has to re-start then load the last "state" from the disk.