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System Builder Marathon: Sub-$1000 PC

The Problem of Bottom-Mounted Power

When Intel designed the ATX form factor, the power supply fan was designated as the primary case fan. Being placed at the top of the case, a power supply could easily draw heat away from the hot CPU and VRM components, expelling it out the power supply’s rear panel. That’s also why ATX power supplies are mounted “upside-down”, with the circuit board on top and the lid on the bottom, so that a lid-mounted fan would also be on the bottom, drawing air out of the case and into the power supply.

The design allowed larger fans to be used, and eventually some manufacturers chose fans as large as 135mm. For most systems, this large fan was enough to take care of all the case’s airflow needs, and that’s true even for today’s mainstream parts.

Moving the power supply to the bottom of the case has several negative effects. First, it takes the power supply’ fan away from the top, so that another fan has to be used to remove case heat, adding noise. Second, it makes cable management more difficult, often times with the ATX12V cable not reaching its motherboard connector. Third, as the power supply casing warms up, it heats the graphics cards.

The only benefit of putting a power supply at the bottom of a case is that the power supply itself runs cooler temporarily, drawing dusty air from under the case until it plugs up. Once the power supply is full of dust, carpet/paper fibers and whatever other small items clutter your desk or floor, the benefit of having its own cooling path disappears.

We excused the power supply location on our high-end build because the change was needed to put the radiator mount on top, accepting the sacrifices needed to achieve our liquid cooling aspirations. But the Centurion 590 doesn’t have enough space above the motherboard to mount a radiator in addition to fans, and our $1000 system uses air cooling anyway.

Unwilling to accept any information pointing to the inferiority of bottom-mounted power supplies, many readers have previously asked questions to invalidate this argument. The most common of these is “If there are so few advantages and so many disadvantages, why have so many companies made the change?” The answer is easy: Because buyers ask them to. Companies will produce whatever customers want, and the reason it took some so long to implement new designs applied long ago by competitors is that most manufacturers chose to wait out the trend, to see if it would stay around, not wanted to produce a design that would be rejected by a change in trends.

Another common question is “Well then, why does BTX have the power supply at the bottom”. The answer is that it doesn’t, at least not by Intel’s design. Some manufacturers have made the switch in their BTX cases for the same reason as above, that is, customer demand.

  • Haiku214
    I'm glad to know that you don't really need a huge amount of wattage to run the 8800 gt sli. How about for the ati 4850 crossfireX? Is 460 watts with a combined 42 amps for the 12V rail be enough?
    Reply
  • hellwig
    Seeing the new prices for components, couldn't you have stayed with the AMD theme, just to satisfy reader curiosity. I.e. 2x3870 in crossfire (or 3870x2) = $300, AMD 790X/FX MB = $125, Phenom 9850 Black Ed = $235 (or 6400+ X2 Black Ed = $160, making room for 2x4850), Plus all cheaper components from current build. You would have still been under the $1000 mark, and the dual 3870/4850 would have given much closer results in the games category, and the unlocked multiplier would have given AMD a little more benefit in the overclocking category compared to the locked 9500 used previously. This would have been more interesting especially since your $2000 PC was really a $1400 PC (the only difference between $1000 and $2000 now being GTS vs. GT and quad vs. dual).
    Reply
  • randomizer
    The first Crysis graph looks more like Very High, not High. I get around 32FPS with a single 9600GT on high at 1440x900.
    Reply
  • cjl
    Considering that those GT's ran you $188 each, even counting a $30 rebate, that should have left 4850's well within your grasp, and they would have significantly outperformed the GT's. In fact, they probably would have outperformed your
    Reply
  • cjl
    Hmm. Looks like it took my less than sign as HTML tagging. That should have said "outperformed your less than $2000 system"
    Reply
  • yonef
    Same problem in here (like in $2000 system build)!
    Tom's realy starts to annoying me:
    First of all: Why the hell you need crapy 8800GT??! while for the same prize you can buy HD4850s http://www.newegg.com/Product/Product.aspx?Item=N82E16814121253 -> 2xHD4850=$330 < 2x8800GT=$386 !!!
    Second of all: 2xHD4850 will easy outperform 2x8800GT even in crysis :D(wich is exclusively for nvidia)
    Third, but not least: How the hell whole system with 2X8800GT will run on 400W PS ?!!? I'm so convinced;
    Reply
  • str8ballistik
    This is really dumb. I love how they add up only a tower. you have to add in the monitor, speakers, mouse/keyboard, etc.. That is what a computer is, not a tower. You get peoples hopes up to buy a computer, then they realize, oh yeah, I have to buy this other stuff to actually be able to use the tower. Come on, be more realistic. I would love to see a mid-rang computer, while seeing what size monitor you can get with it.
    Reply
  • randomizer
    yonefWhy the hell you need crapy 8800GT??!It's funny how a suddenly card becomes worse when another card is released better than it, even funnier when a few weeks ago this was THE card to buy. Did you stop to consider when this article was written? Perhaps the card wasn't available when they wrote this, and in order to get the article out on time they had to go with "crappy" cards.
    Reply
  • mf_fm
    AMD + ATi FTW $1000 system
    Reply
  • giovanni86
    If u don't already own a monitor/keyboard/mouse/speakers n your reading this thread you are a retard. Like seriously why would you not own those things already. Personally i like these articles they make, it puts together a PC built tower for you already kind of knowing what u could get at such a great price point. And 2ndly in my opinion ATI has nothing on NVIDIA, although ppl claim it to be better and cheaper then NVIDIA's line up i beg the differ. And 3rdly i can't believe that a sli system as well could run off a 400watt PSU.
    Reply