w_tom said:
How to separate the responses. Do they provide numbers? Do
they mention information from manufacturer datasheets? Do
they explain the science behind the reasoning? Do they reply
using principles you were taught in Junior High School science
- it must have both theoretical reasoning - the principles AND
it must include experimental evidence - the actual numbers
from industry experiments and datasheets.
A power switch has a life expectancy of (typically) 100,000
cycles. Clearly power cycling a switch is far more
destructive than leaving it on. Lets see. Power cycling
seven times every day for ... 39 years.
Another device that has a particularly small 'power cycle'
life expectancy is one particular IBM hard drive - 40,000
cycles. That is seven times every day for ... 15 years.
The idea that power cycling shortens life expectancy is
correct - until we apply engineering numbers and put those
numbers into perspective. Then power cycling worries belong
in a myth category. Some devices may have a shorter life
expectancy such as that power switch and that disk drive. But
who cares? Once numbers are applied, then reality takes on a
whole different perspective.
Some components, such as CPU are power cycling most severely
when in normal operation. Did they forget to mention that?
If power cycling was so destructive to a computer, then it is
also so destructive to a TV. If power cycling shortens a
computer's life expectancy by a factor of ten, well, who cares
if the computer is still working 150 years from now.
Those who say 'leave it on' never meet the criteria for
scientific response. A glaring missing detail - they post no
numbers. That alone says the post has no credibility. No
numbers suggests junk science reasoning. When done, turn it
off or put it to sleep. Clearly the best solution is we
eliminate those who post only their personal speculations -
not tempered by the numbers.
Too much 'general feeling' is easily confused by those who
don't have numbers. Too many eyes glaze over when the numbers
are provided. But the answer to your question is found in
numbers - that junk scientists fear.
We speculate because we don't have numbers. Then get
numbers so that we have knowledge. Now start filtering out
posts that only speculate. Your final answer will become
obvious.
The last definitive numbers that I saw on this were from the mid-1980s
and were based on a study of computers at a University. These were
IBM AT (80286 CPUs) models. One group of the computers were installed
in a computer lab where they were turned on at the beginning of each 1
hour class and turned off at the end of that class. The other group
were installed in administration and faculty offices where they were
switched on at the beginning of each work day and off at the end of
the day.
The computer lab machines began to encounter high rates of hardware
failures (hard drives, RAM chips, motherboards, etc) after 18 months
of use while the admin and faculty office machines were pretty well
failure free after 3 years of use.
Of course hardware reliability has improved by at least one order of
magnitude since the mid 1980s but I believe that the factors
identified with regard to the above noted study are still relevant.
These specifics include:
1. Hard drives contain electric motors, and like all electric motors
are under the greatest load and therefore the most stress when they
are first powered up. The vast majority of electric motor failures of
all kinds, including refrigerator compressors, washing machine pumps,
etc. occur when the machine is powered up not while it is actually
running.
2. Electronic components are comprised of different layers of
materials. When power is applied to these components they become
heated and with this heating there is expansion. However the
different materials have different rates of expansion and therefore
when they expand there will be stressed placed on the joins between
these materials. And when the power is turned off the materials
contract and the stresses are relieved. Repeated stressing and
unstressing an object at the same point gives rise to a condition
known as "metal fatigue" and the stressed item is likely to break or
crack at some point because of this. Such a breakage or cracking
within an electrical components would, of course, most likely result
in the total failure of that component.
But as "Bill" pointed out in his response the improvements in hardware
reliability means that computers will be disposed of due to
obsolescence long before these hardware effects reach any sort of
critical level.
Ron Martell Duncan B.C. Canada
--
Microsoft MVP
On-Line Help Computer Service
http://onlinehelp.bc.ca
"The reason computer chips are so small is computers don't eat much."
