7800GT/GTX Minimum CPU?

I have been meaning to upgrade for a while and was going for either an
Radeon X800XL or a Nvidia 6800GT. I'm now tempted by the new 7800, but
wonder if it's a waste of cash with my processor, a P4 3.4ghz (800) with
a 460W power supply in my PC. I keep reading that these cards are CPU
limited? Also can anyone tell me if I can connect the 6800/7800 power
connector up to just one power cable from my power supply or are two
power cables needed to connect up to the two molex connectors that I see
with the adaptor supplied with most cards. Many thanks for any feedback
:-)

Prof Rumpo kirjoitti:
I have been meaning to upgrade for a while and was going for either an
Radeon X800XL or a Nvidia 6800GT. I'm now tempted by the new 7800, but
wonder if it's a waste of cash with my processor, a P4 3.4ghz (800) with
a 460W power supply in my PC. I keep reading that these cards are CPU
limited? Also can anyone tell me if I can connect the 6800/7800 power
connector up to just one power cable from my power supply or are two
power cables needed to connect up to the two molex connectors that I see
with the adaptor supplied with most cards. Many thanks for any feedback
:-)

You CPU is definitely more then adequate, it's far above average today.
Your PSU too is well above average so it should be enough aswell. It is
however recommended that you do not share the power connector with other
devices (with hard drives or cd/dvd drives). According to NVidia website
FAQ 350W is enough for a single 7800 card (500W recommended for SLI).
Also a single power connector is used, the adapter you are referring to
is most likely a connector splitter in case all connectors are in use
already.

"vellu" wrote in message
...
Prof Rumpo kirjoitti:
I have been meaning to upgrade for a while and was going for either an
Radeon X800XL or a Nvidia 6800GT. I'm now tempted by the new 7800, but
wonder if it's a waste of cash with my processor, a P4 3.4ghz (800) with
a 460W power supply in my PC. I keep reading that these cards are CPU
limited? Also can anyone tell me if I can connect the 6800/7800 power
connector up to just one power cable from my power supply or are two
power cables needed to connect up to the two molex connectors that I see
with the adaptor supplied with most cards. Many thanks for any feedback
:-)

You CPU is definitely more then adequate, it's far above average today.
Your PSU too is well above average so it should be enough aswell. It is
however recommended that you do not share the power connector with other
devices (with hard drives or cd/dvd drives). According to NVidia website
FAQ 350W is enough for a single 7800 card (500W recommended for SLI). Also
a single power connector is used, the adapter you are referring to is most
likely a connector splitter in case all connectors are in use already.

From an electrical standpoint, it shouldn't make any difference whether you
connect the video card to a separate connector or to a connector that's
shared with other devices unless you have a power supply with multiple rails
and you know which connectors are on which rail. If there's only 1 rail,
then all your devices are connected in parallel anyway, so what am I missing
here?

--
NoRemorse
"Expect me when you see me."

From an electrical standpoint, it shouldn't make any difference whether you
connect the video card to a separate connector or to a connector that's
shared with other devices unless you have a power supply with multiple rails
and you know which connectors are on which rail. If there's only 1 rail,
then all your devices are connected in parallel anyway, so what am I missing
here?


True, it depends on your PSU. I've seen PC's where it made no difference
which power connector was used (all worked) and PC's where it only
worked when the GPU had it's own connector.

'NoRemorse' wrote, in part:
| If there's only 1 rail,
| then all your devices are connected in parallel anyway, so what am I
missing
| here?
_____

You are missing a small factor. There is a certain amount of resistance in
copper wire, and a certain amount of contact resistance at each connection.
At high currents and low voltages this resistance can cause a significant
voltage drop. The move from 5 volts to 12 volts for on-motherboard CPU
DC-DC voltage downconvertors/regultors is to help reduce this effect. The
same is true for the direct 12 volt DC connection to high end graphics
cards. ATX +12V power supplies regulate the voltages as measured at a point
inside the power supply, not at the point of delivery. The difference in
the two voltages is tiny for low current circuits, but is larger for high
current cirucits. A hard drive and a graphic adapter on one + 12 volt line
from the power supply shouldn't be a problem, but there will be a slightly
higher voltage drop. Even if the resistance of the ground wire + 12 volt
wire + contact resistance is only 0.01 ohms, the voltage drop will be more
than 0.1 volts if the current drawn is 10 Amperes. At some point this could
become a problem - if contact resistance is higher and/or current draw is
higher. (The Molex connectors used on power supplies have a limited current
rating, that's why for the + 12 volt CPU connector there are two + wires and
connector pins and two - wires and connector pins, otherwise the current
ratings could be exceeded.

For the same reasons, automotive electrical systems are moving to ~ 48 volts
from 12 volts; lower voltage drops, less wasted power, and smaller wires and
connections.

E=IR


"NoRemorse" wrote in message
...
"vellu" wrote in message
...
Prof Rumpo kirjoitti:
I have been meaning to upgrade for a while and was going for either an
Radeon X800XL or a Nvidia 6800GT. I'm now tempted by the new 7800, but
wonder if it's a waste of cash with my processor, a P4 3.4ghz (800) with
a 460W power supply in my PC. I keep reading that these cards are CPU
limited? Also can anyone tell me if I can connect the 6800/7800 power
connector up to just one power cable from my power supply or are two
power cables needed to connect up to the two molex connectors that I see
with the adaptor supplied with most cards. Many thanks for any feedback
:-)

You CPU is definitely more then adequate, it's far above average today.
Your PSU too is well above average so it should be enough aswell. It is
however recommended that you do not share the power connector with other
devices (with hard drives or cd/dvd drives). According to NVidia website
FAQ 350W is enough for a single 7800 card (500W recommended for SLI).
Also a single power connector is used, the adapter you are referring to
is most likely a connector splitter in case all connectors are in use
already.

From an electrical standpoint, it shouldn't make any difference whether
you connect the video card to a separate connector or to a connector
that's shared with other devices unless you have a power supply with
multiple rails and you know which connectors are on which rail. If there's
only 1 rail, then all your devices are connected in parallel anyway, so
what am I missing here?

--
NoRemorse
"Expect me when you see me."