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Hard (disk) drives (101)

First. A hard disk drive is just one part of many parts that make up a computer.

• Disk drives (HDD or SSD) are computer storage devices where applications are installed on, and data (documents, pictures, music, etc.) is saved to.  If you have saved your work, shutting off or rebooting the computer does not affect what's on the hard drive.  (But see hard drive failures.)
  
• Memory (RAM) gives the computer muscle and speed.  Applications and data are temporarily copied to memory from the disk for processing.  Shutting off or rebooting the computer clears whatever is in memory.
  
  • Memory is used between the disk and processor because it is much faster than processing directly from/on a hard drive (solid state or not).

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Hard drives are the device(s) where your data (files and folders) are stored.  If you are getting rid of a computer and are concerned about what data may be saved on it, remove and destroy the drive(s). 

Hard drives (HDD) and the newer Solid State Drives (SSD) operate basically the same way, but two major distinctions:

• HDD have moving parts and will wear out.  But they are prone immediate failure if moved abruptly and/or the power fails.  If a physical shock occurs, the arm may contact the spinning platter destroying the drive, so don't move computers around while they're running, but we digress...
• SSD have no moving parts hence withstand shocks and movement but they are relatively small, expensive (explain that one) and just like a mechanical drive, SSDs have a maximum life. 

Lifespan:  Everything fails sooner or later, but assuming there are no abnormal occurrences (being dropped, power outage, etc.) both type of drives will last for many, many years.  However, a maximum life is very apparent by the manufactures warranties (or lack there of).  Most have a maximum of three years but commonly just one.

• Hard drives can fail without any warning or slowly fail/wear out where you may (or may not) get a impending failure notice on boot up.  Those failing over time typically exhibit extremely slow computer operation where the hard drive indicator light is consistently lit even though the computer is apparently doing no work.  But to be clear, a constantly working hard drive could also be indicating a virus, junkware or other software issue.

UPS - power backup systems

We are a huge fan of using uninterruptable power supply (UPS) units having all of our computers AND all of our network devices (routers, switches, etc.) on individual UPS units.  Electronics and as mentioned above, hard drives do not like a sudden loss in power, e.g., power outages.

Be careful not to overload their capacity.  Never plug a laser printer into a UPS, even on the surge protection side.  Lasers initially draw a lot of power and can damage the UPS.

UPSs are rated by wattage and how many minutes they will maintain electricity to the device(s) connected.  A typical computer and monitor can be kept running for 10-15 minutes on a 350 watt unit.  Much longer if you get 1,000 or larger units.  A network modem, router and switch can get by on a 350 or so.

Most UPS devices have software available to monitor voltage drops and in a power outage situation, can safely shut down the computer when the battery is becoming low...