Re: what is the purpose of -ve voltage in PC?

"gchandrujs via HWKB.com" <u25485@uwe> wrote in message
news:72a4666beb021@xxxxxx
Hi,
I want to know what is the purpose of -ve voltages in PC ? for
example -5v, -
3.3v, -12v. It knows to a common man that +ve voltages flows current and
i
would like to know the purpose of -ve voltages.
Think of the 'flow', like a water circuit. Water can be pumped round the
circuit in either direction, but there always has to be a complete
'circuit'. In fact the actual electron 'flow' in a circuit, is the
opposite way to the 'sign', so it is the -ve connection, that 'sources'
electrons, and the +ve ones, have the electrons flowing towards them!.
With the positive connections, electrons are flowing 'out' from the 0v
wire, through the circuit, and back into the +ve connection. With the
negative connections, the electrons are flowing out of these connections,
through the circuit, and back into the 0v pin. It is one of the oddities
of history, that we have the flow 'backwards', from what would seem
intuitive...
Now, just as with the water analogy, there can be places where water needs
pumping 'up' (cistern in the roof for example), and others where flow in
the other direction is needed. Most modern stuff, doesn't really use
the -ve rails now. Instead if -ve lines are needed, the circuits will
contain their own 'charge pump', to provide these rails, drawing the
required power fom the +ve rails, and moving this where needed (the
circuit used, works just like a 'bucket brigade' of firemen). However in
the past, this was much harder to do, and so -ve rails were provided. The
basic uses were:
The -5v rail, was required by the original memories on the PC. Modern
memories generate their own internal rail.
The -12v rail, was used by the RS232 signalling standard (to improve noise
immunity, quite a large signalling voltage is used on this, -12v to +12v
normally at the 'source').
This rail was also commonly used by audio circuits, which want their
output voltages to have 'symmetrical' swings around the 0v rail.
There isn't a -3.3v rail in the AT.

Also can you get me some links for easy understanding for power
consumption
of a PC and SERVERS which can be in easily understandable manner?. In
general
we identifying power consumption by adding all the power consumption of
peripherals like keyboard, motherboard, PCI devices etc., But May i know
what
power consumes generally PIII, PIV PCs consumes per hour ?

Varies massively. The processor itself, depending on speed, and what is
actually being done, can draw anything from about 10W, to nearly 200W.
Most current units are specified to dissipate about 90W max). The second
biggest user, is the video card, with some of the modern high performance
cards having 'peak' demands well over 100W. Systems using two such cards
in SLI, or a similar manner, can have huge demands in this area. However
quite competent basic displays can be done using well under 10W, and
typically cards like this will be used in server applications. Disk
drives, use between about 2W (some low power designs), up to nearly 30W
5W/GB (depends on the speed as well). Keyboards/mice etc., will all use
under 5W (remember this is the maximum a USB device can draw without
external power, and hence provides a good 'guideline').

Best Wishes

.

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