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Gerbil First Class
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PSUs in the bottom of the case. Didn't they try this before?

Mon Mar 02, 2009 1:30 pm

I saw a few performance cases with the PSU mounted in the bottom of the case, underneath the GPU/CPU/motherboard, and I don't understand why this has returned from the pre-GPU era.

I remember something I think was called a "BTX" standard where they had the PSU mounted under the motherboard/CPU and air was directed in to the case, through the PSU, up to the CPU, and then out of the rear of the case. This was back for Pentium II's I think. Maybe it was the III's. But it was a long time ago and it was hastily abandoned because the idea was to suck in cool air, warm it, and then send it to the CPU. This turned out to be as bad as it sounds.

Admittedly the PSU's in use now are many times better than the old PSU's in every single way, but I've seen these new cases with a somewhat similar design and it made me worder if this is suddenly a good idea now. The dork at my local computer shop thought it was the greatest thing but he's a local computer shop dork and I doubt he remembers the BTX standard. So I come to the forums to get your take on this.

The PSUs now moved air much better, warm it less, but does that make them worthy of use as part of a air deliverly system to the CPU? The cases now are designed much better now as well, so maybe I am wrong in assuming this air is circulated to the CPU at all. Is it exhausted before reaching the CPU/GPU?

Does this new implementation of the PSU's in the bottom of the case work? How does it move the air? Does it even seem like a good idea?
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Gerbilus Supremus
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Re: PSUs in the bottom of the case. Didn't they try this before?

Mon Mar 02, 2009 1:35 pm

There are different implementations of this design, most of them have the PSU in a separate area of the case. The big motivation is to prevent hot air from the CPU area from entering the PSU.
Gerbil Elite
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Re: PSUs in the bottom of the case. Didn't they try this before?

Tue Mar 03, 2009 12:17 am

Are you thinking of some form factor other than the BTX? Intel released that around the time of netburst, 5+ years before Pentium IIs.

My old BTX cases from Dell didn't intake air through the PSU. Considering ATX and BTX use the same standard for PSUs, I bet all BTXs exhausted air through the PSU.

Are you sure the PSU at your local computer shop drew in fresh air and then sent the hotter air towards the cpu and gpu?
Grand Admiral Gerbil
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Re: PSUs in the bottom of the case. Didn't they try this before?

Tue Mar 03, 2009 12:43 am

You're confused about how BTX worked, and you're mistaken about the cases with the PSU at the bottom. Every one I've seen blows air out of the case. In fact many/most of the cases that mount the PSU at the bottom don't even include the PSU, and if you mount a standard PSU in there it will exhaust the air out of the case just like it would if it was mounted at the top. To get the PSU to suck air into the case you'd have to mod it to spin the fan backwards. In fact one of the reasons to have the PSU at the bottom is to eliminate what is usually a "dead" airflow zone in that part of the case, particularly now that "blow-hole" fans are common. The other reason is to move the center of gravity downwards so the case is less top-heavy.

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