Computer Power

To power off or not to power off, this is the question

I have heard various arguments for either side of this debate for years.  The "advice" I hear sometimes is that you should just leave your computer on all the time rather than shut it down at the end of the day because (choose one or more: It consumes less power than starting up each day, It's better for the hard drive, It wears down the computer less, Electrical components that expand or contract with temperature variations take less wear, Less chance of electrical power surges, or It's quicker than booting).

All but the last explanation are false.  Here is a refutation of each reason:

Leaving your computer on consumes less power than starting it up each day

FALSE.  While a computer is on, the processor is continuously using power to perform "Idle" functions, or tasks that hardware devices or the operating system need done periodically.  These may run once an hour (virtual memory caching) or one thousand times a second (checking for input from the keyboard or mouse).  All these tasks consume power on top of spinning the hard drives (if set to stay on), running the fans, and converting the power.  This last item is particularly important. 

All computers convert the standard AC (alternating current) power we all have in our houses to DC (direct current) power.  During this conversion some power is lost to heat.  This, in part is why your computer gets hot, and also why leaving your computer on does not, in any way imaginable, save power.

Finally, part of this claim usually contains the assumption that the initial "spin-up", or start-up of the hard drive, as well as the various start-up tasks the computer must do when starting from a power-off condition, consumes a disproportionately large amount of power.  This claim too is false. It can easily be shown false with a simple calculation. 

A standard computer operates at about 8 Amperes per second, or amps (see here for the calculations).  If it takes five minutes to start a computer up, then the most power a computer can possible consume without blowing up is 2,400 amp's.  Now, a standard transformer (mentioned above to convert the AC power to DC) takes at least 1 watt (at 12 volts that's .08 amps, source).  If, by some miracle, no more power is consumed in the computer all night (10 hours) accept for the transformer, 3,000 amp's are consumed.  So there you have it, a five-minute burst of all-out computer power is still less than just running one small component (not even the CPU) all night.  Add the idle processor functions, fans, and hard drive, and over night your computer can consume more than 20,000 amp's (Note: I pulled this last number out of my ass, so prove me wrong if you think it's inaccurate).

Leaving the computer on is better for the hard drive than starting it up each day.

FALSE.  There are two reasons.  First, unless you have changed the settings on your computer, it already turns the hard drive on and off all day.  Hard drives are manufactured with auto-spin-down feature that ensures less power is consumed when the hard drive is not being used.  It's a stretch to say that a core function of a hard drive (turning on and off) causes damage when a vast majority of consumer PC's do it every day without major problems.

Second, spin-ups and spin-downs are more simple, mechanically, than the read/write functions of the hard drive.  A hard drive consists of several main components: the platter, which is a flat disk where the 1's and 0's are stored magnetically, the head which moves across the platter to read and write the 1's and 0's, and the motors which drive these devices.  During a spin-up (or power-on), the platters must be brought to a particular speed (usually 7,200 rotations per minute) before any data can be accessed on the hard drive.  The time required to do this is reported by manufacturers of hard drives for each model they produce.  Typically, it takes from 1/2 to 3 seconds to perform this operation.  After a spin up, the head performs some basic hardware test functions, accesses parts of the platter to ensure the data is there, then is ready to operate.  The only thing different from a start-up and standard reading and writing that occurs with normal computer use is the platter spin up, which is a short, 3 second (at most) operation.  There is no more friction, resistance, or any other variable that would make a spin up more hazardous than just maintaining a spin other than a little additional power.

Leaving the computer on wears the computer less than turning it on and off all the time.

FALSE.  Wear occurs in two main categories: moving parts and non-moving parts.  Let's review the major moving parts of a computer: hard drive, CD-ROM, disk drives, power supply, keyboard & mouse, printer, fans, etc.  Of all these, the only that would run in the middle of the night are the hard drive (if forced or being used), the power supply, and fans. All three of these components will wear in direct correlation to the amount of time they are used.  Simple and direct, leave it on, it's used more, thus more wear.  Arguments that more wear is incurred when first starting up are refuted in the previous section.

The second type of wear is addressed in the next section:

Leaving the computer on reduces wear from the expanding and contracting of electrical components.

FALSE.  This seems like a reasonable argument, and is based on simple physics. According to thermal expansion equations, a metal will expand and contract at a specified rate as the temperature changes.  This equation assumes that the temperature change is happening to the metal, not just the air around it. 

Firstly, motherboards are made of materials, like silicon, gold, and copper that have low expansion coefficients (source). Secondly, the manor in which printed circuit boards are made, expansion and contraction is not an issue unless super-heated.  This is why all computers have recommended operating environments (see the sticker on the back of your computer).  As long as the computer stays within these temperature extremes, "it's all good." 

Additionally, in this case the opposite is true.  Heated components of the computer are more excited (more energy): the atoms move around more.  By cooling them down when possible, you reduce the frictional wear that occurs naturally when certain metals are heated.

There is more of a chance of power surges when starting up as opposed to leaving the computer on.

FALSE. There are two issues here, external power surges, and internal short circuits.  Power surges are caused by turning on and off electrical appliances, lightning, and faulty equipment.  While there is a risk of a power surge when initially starting up any electrical device, a computer is not necessarily free and clear once it's running.  Most power surges in the home occur as the result of air heating and cooling devices, hair driers, washing and drying machines, and electrical storms (source).  Thus, the longer your computer is exposed to these surges, the greater the chance of damage.  This is why everyone recommends that surge protectors are used with computers.  This is also why most computers have fuses, which stop electrical activity if an internal surge occurs.  Shortly, use a surge protector and you don't have to worry about surges. 

Short circuits occur in computers when the electricity inside the computer suddenly finds a quicker route through it's path, causing a brief surge in power.  Your computer will not short circuit unless the electricity is physically given a shorter path, either by putting your greasy hands on the circuit board, or by the failure of an electrical component.  While component failure is rare, it happens and it usually means buying a new computer.  Not running power through these components while they are not needed will ensure that the life for these devices is as long as possible.  Also, not putting your hands on the circuit boards is a great idea too.

It's better to leave your computer on because it takes too much time to start it up.

TRUE.  Hey, no argument here.  How much is three minutes worth to you?  Personally, the arguments "10 hours idle time is worth saving three minutes boot time", or "10 hours of power is worth less than three minutes of my time", or "The risks with increased wear are worth saving three minutes each day" are ridiculous.

Conclusion

Per the arguments above, leaving your computer on consumes more power, causes more wear, and produces more heat than turning it off.   If you think it's worth risking wearing out electrical components and consuming copious amounts of power to save a couple of minutes each day, more power to you (literally).  However, if you are blessed with a particularly objective and rational mind, you will see quite clearly, that turning your computer off (or using the hibernate feature) is for the best.

If you're not convinced, here are some additional reasons to turn your computer off (or standby/hibernate) every day:

• Lower power bill (as proved above)
• You're computer's memory (RAM) is fresh, thus the computer runs better.  Extended computer use results in memory fragmentation that slows operations.  Every time your computer boots (NOT when you standby/hibernate), the memory is cleared.
• Windows XP downloads updates automatically that occasionally require restarting.  Simply booting each day takes care of this.
• Allowing components to cool reduces wear.  Remember, heat = energy, and over time energy breaks down components.
• Unless you're running a web server, there really is nothing a personal computer could do over night that it couldn't do during the day while you're using it.  The computer spends much of it's time waiting for you to do something anyway!

Happy computing!