Gpu psu spec confusion

[yosimba2000]

why are the wattage specs for any graphics card different in:

Maximum Graphics Card Power (W)

and

Minimum Recommended System Power (W)

for example, looking at the 9800gt under nvidia's site, it says that the Maximum Graphics Card Power is 105 Watts, but it says that the Recommended System Power is 400 Watts. Why are these two values different? Thanks!

 

[hunter315]

The graphics card itself will only draw up to 105W at stock settings, however, other things in the system need power so you shouldnt have it in a system that has less than a 400W power supply, thats what those numbers really mean. The max graphics card power is a realistic number, the recommended system power isnt usually too close, its often done with a large high powered system and gives the smallest you should have, however there are some crappy units out there and not all 400W units are created equal and thats something it cant take into account so they will often round up a bit to cover themselves.

 

[ko888]

Maximum Graphics Card Power is the maximum power that may be drawn by the graphics card itself.

Minimum Recommended System Power includes Maximum Graphics Card Power and a power allowance needed to power a typical CPU, motherboard chipset and on-board devices like LAN and audio chips, hard disk drives, CD/DVD drives, expansion cards, cooling fans, etc. in a system.

 

[kajabla]

When you get a PSU, make sure it's a decent one. Don't get some $10 "400 W peak power" piece of scrap metal. An Antec 380 or Corsair 400 would be good choices.

 

[beanoslim]

You can never have too much power but not having enough is a real issue.

 

[ko888]

for example, looking at the 9800gt under nvidia's site, it says that the Maximum Graphics Card Power is 105 Watts, but it says that the Recommended System Power is 400 Watts. Why are these two values different? Thanks!

What's really missing in the GeForce 9800 GT's specifications, and probably the most important specification (i.e. even more important than the power supply's Wattage), is the power supply's Minimum Recommended +12 Volt continuous current rating of 26 Amps.

You also need to pay attention to the number and types of PCI Express supplementary power connectors are required on the power supply to meet the graphics card's requirement.

 

[yosimba2000]

oh btw, what exactly is a "12 volt rail"? and how about Amps vs Volts? i know i should google it but i g2g now so thx.

 

[hunter315]

A "rail" is simply a bunch of current carrying wires all tied into the same overcurrent protection circuit. In the case of a 12V rail they are all at 12V relative to ground, and are all monitored as a single grouping by the protection chip.

As for what a volt and an amp are, water makes a decent example for electrical systems, a voltage difference is the difference in potential energy between the source and ground(sea level in this case), the greater the difference the faster it flows, amps tell you how much energy is being delivered(the amount of water flowing through a point) so if you have a very fast river thats very shallow it wont move as much power as a wide, deep, and reasonably fast river. Something important to remember, watts=volts*amps, so you can figure out the power available on a rail that way