Re: more on saving during power out

George Graves wrote:

> The difference between a UPS and direct battery backup may seem subtle
to 
> some and even nit-picking, but it is actually two totally different 
> approaches to the same problem. 
> 
> An uninterruptable power supply (UPS) uses a battery, yes, but it
doesn't use 
> one directly, it uses the battery and a DC to AC converter to change the
DC 
> battery voltage (usually 12 volts, but it can be something else) to 120
V (in 
> the USA & Canada), 60 Hertz mains power. The computer user merely plugs
his 
> computer's mains cord (AC cable) into the receptacle on the UPS unit and
the 
> UPS unit plugs into the wall. Normally, the AC coming out of the wall
p***** 
> through the UPS box and on to the computer. Some of the AC is used by
the UPS 
> to maintain the battery's charge and most use lead-acid or gel-cell 
> technology because the usage is a lot like that in a car or motorcycle 
> battery and is an ideal application for this type of cell. 

I usually go for the UPSs that never pass through the AC power but 
always run the devices on conditioned power.   Such as APCs 
"Smart-UPS" line, versus their "Back-UPS" line.

> When the power
> fails, the UPS instantly kicks over to battery whereby the DC/AC
converter 
> maintains the power line voltage so that the computer does not shut down
at 
> all. Depending upon battery size (capacity) the UPS can maintain
computer 
> operation for any amount of time from a few minutes to hours. Most UPS
units 
> for home computers have relatively small batteries in them and these
usually 
> come with some software to tell the computer (either via Ethernet or
USB) 

Normally RS-232 serial, with USB just starting to become more normal, 
though the APC unit I just bought a month or so ago for $500 only has 
RS-232 serial.

> that main power has failed. This software will then initiate the proper 
> shutdown sequence for the computer: Save all work, close all open 
> applications, and properly shut down the computer.

How "graceful" that saving of work and closing of apps has  a lot to 
do with the OS and the applications involved.

Steve