Laptop PSUs versus Desktop PSUs inregard to GPUs

Just a quick question I was hoping someone could shed some light on. For example purposes I will use the NVIDIA 8800GTX & 8800M GTX GPUs.

In todays desktops we all know that it is the GPUs that are requiring the need for higher and higher wattage power supplies. Top of the line GPUs are now requiring over 600W PSUs to power them.

The 8800GTX 512MB requires a minimum of 400W PSU. In comparison a laptop with a 8800M GTX 512MB has an average PSU wattage of 120W. The difference between the mobile GPU and desktop GPU are very minimal MHz wise...

-------------CORE----MEM----SHADER
8800 GTX---575MHz, 1350MHz, 900MHz
8800M GTX-500MHz, 1250MHz, 800MHz

Why is it that desktop GPUs need so much more power?

 

This is a question id liek to know too, i dont get why desktops cant be lower powered, the performance difference between the notebook and desktop versions of componants is minimal and usualy cant be noticed other than in benchmarks.

strange...

 

Well a big difference is voltage requirements and higher clocks. Take my gtx 260 for example. Under full gaming mode it runs the voltage at 1.11. My old 8800m gtx gpu at full load I believe was 1.00 even. While its only off by .11 its actually quite a large difference. Also the laptop gpu's range anywhere from 100-200 mhz difference on the gpu core compared to their desktop counterparts. Another difference is the actual number of cores on the gpu. The 9800m gtx, nvidias most powerful non workstation gpu only has 118 shader cores as apposed to their highest desktop gpu using 240.

Another difference in laptop vs desktop realm is the psu. For some reason tons of desktop gpu's are still horribly inefficient. Several reviews of the sager np9262 laptop with a psu rating of 260 watts consumes 220 watts. The efficiency rating has to be somewhere in the high 80's to low 90's. Compared to a desktop psu which is pretty standard to be rated at 85% or lower.
Anandtech did a pretty good review a while ago about desktop psu's.
http://www.newegg.com/Product/Product.aspx?Item=N82E16827118009

The point was that it comes down to a couple key factors with desktop psu's , efficiency, wattage and amps your psu can support. If there was such a thing as a 50 amp 400 watt psu with a 95% efficiency rating you could pretty much run just about any non sli desktop. Unfortunately they really don't make a 400 watt psu with two pci-e connectors and a 50 amp 12 v rail. Also a 95% efficiency rating psu would probably cost you a arm and a leg. So instead we end up with psu's in the 500-600 range with 80% efficiency that have 38-60 amp 1-3 12v rails.

As laptops continue to overtake desktops in sales, I'm sure we will stop seeing desktop gpu's produced for desktops and then modified for laptops. We should eventually see them designed for laptop standards and then modified or overclocked for desktop usage.

Edit: for the two specific models you compared, the 8800m gtx uses a 256 bit bandwith with 96 shader cores while the 8800 gtx desktop uses a 384 bit bandwith using 128 cores. The 8800 gtx uses a 90 nm core fabrication while the 8800m gtx uses a 65 nm fabrication process. I like to use a site called http://www.gpureview.com/. It makes comparing graphics cards very easy.

 

A small note - the power supply requirements listed by Nvidia and ATI for their video cards are for POS inefficient power supplies. You could run an 8800GTX 768MB on a good quality 400W PSU from Corsair or PCP&C. It's the amps on the +12V rail(s) that matter, not the watts. A lot of other factors come into play as well - the stability of the +12V rail, and the list goes on. Too complicated to discuss here.

Good quality desktop power supplies are rated for the specified output at real-world operating temperatures of 40 - 50*C, unlike cheap no-name power supplies which are rated in a freezer - i.e. impractical conditions.

Typical desktop power supplies are probably rated around 60 - 70% efficiency, which is low and therefore you'll have a lot of wasted energy in the form of heat. Excellent quality ones are 80 PLUS certified, which means they have a greater than 80% efficiency rating and meet a number of other standards. I have a Corsair HX620W PSU, which produces very little heat even under full load - that is because it is extremely efficient (up to 88%).

To continue desktop discussion, I suggest going over to DesktopReview.com and discussing there. If you registered on NBR in the last six months your account is probably already over there.

 

I believe that the rating that the PSU's are also taking into consideration especially the desktop version is that desktop components such as the CPU, Hard Drive, Disk Drives, etc. take up more wattage than their laptop / notebook counterparts. Hope this helps. God Bless

 

Does the fact that some desktop cards have their own internal fan(which therefore also uses power) come into play?

 

nope, most laptop gpu's also have their own dedicated fan, just about anything 15.4 and above comes with two fans, one for the cpu and another for the gpu.

 

Those two are using different GPUs. The desktop 8800GTX has the G80 core, built on an old 90nm die process, and the 8800M GTX uses the G92, which is a heavily revised core based on the G80, but with a smaller memory bandwidth, and most importantly, optimized stream processors, and a smaller 65nm die process. Die shrinks play a major factor in heat output and power consumption.

EDIT: I didn't read the whole thread thoroughly, but bwhxeon got it covered. It's not a good comparison between the two, since one is using an optimized core based on the other. The desktop 8800GTXs were very hot, power hungry cards. The 8800GT/9800GT and whatever cards that uses the G92 core showed massive improvement in temperature and nearly cuts the power consumption down by 50%.

 

There is still a huge difference in the wattage needed to power a desktop as opposed to a laptop and the desktops requirements keep going up up up while laptops have remained pretty much the same...

I am sure PSU manufacturers have been loving the GPU manufacturers for the last 5-6 years... Esp NVIDIA for bringing back the whole dual video card thing that I believe Voodoo tried ages ago...

My home desktop has a core 2 duo 6600 with a single 8800GTX and I am using a Corsair PSU over 500W cant remember exact Wattage atm. I know I paid quite a bit for it.

I will be curious to see the difference in benchmarks between my new laptop and my old desktop... If the laptop does out perform it.. I believe my days of building my own overly power hungry desktops is over and I will have converted to a 100% laptop guy.. Looking forward to the day when we can completely piece together our own laptops for a decent price.

 

Here is the real question. Why does a Laptop require ~19v, when we know there is nothing in a desktop that requires anything over a 12v rail? What is it in a laptop that needs so many volts? The screen?

 

I had this same issue about 3 years ago with a "desktop" replacement laptop I bought. Although it mothballed my desktop for a few years. It wasn’t long before games were choking out my laptop. When faced with kicking down ~$1400 for a nother "desktop" replacement laptop or spending ~$300 to upgrade my desktop, I'm sure you know what I chose.

 

Well I have an XPS M1730 with 8800m GTX SLI that has a power supply of around 220v I think. That is pretty good considering it is two GPU´s running in SLI and two HDD´s in Raid 0.

I also have a 8800GTX desktop, but I can say my 8800m GTX SLI outperforms it in games. I benchmarked against a guy with a desktop 4870 same res same settings and I outperformed him in the two games we tested. So there is some real power packed in such a limited space and small power supply

Now I don´t have to worry about electricity since my electricity is for free so no bills for me in that matter.

 

Paying a lot for electricity while I was in Germany is what really made me start thinking about all of this. Wife and I both game so multiply the power usage by two, stationed in California now so electricity is still expensive.

Good point about the upgrade costs of a desktop as opposed to buying a new gaming laptop. I had upgraded my desktop right before Crysis came out but I usually end up upgrading everything which costs just as much as buying a new Laptop.

 

Not really @ upgrade costs... the desktop I just built (Specs in sig) cost me $765 and that includes a 22" monitor, the system itself minus monitor was $585. My laptop in sig was $880, and it's solidly mid-range. My desktop, at $765, performs better than a laptop that costs $3,000+ (NP9262 decked out with dual 8800M GTX) If you need a gaming notebook or want to cut down on power utilization, that's one thing, but it's an absurd argument that it's more cost effective.

 

Lets look at it this way. If a $1000 desktop performs the same as a $3000 laptop. Then, you would need to save at least $100 a month in electricity bills to make up the price in 20 months. I doubt any laptop is that energy efficient.