reasons for cpu location on mobo

[jcarte01]

Hi
I'm designing the layout of a new pc. most (tower) cases have the pci slots towards the bottom and cpu in the upper third of the case. i was wondering if there was a reason for this, thermal or otherwise. i was thinking of having the cpu lower in the lowest third of the case and use its cooling fan to suck cooler air into through a duct. and use the psu fan to blow the warmer air out.

Homer: There’s 3 ways to do things, the right way, the wrong way, and the max power way.
Bart: isn’t that the wrong way.
Homer: yea but faster.

 

[fishmahn]

I believe the history of it goes like this:

In the beginnin was the word... and the word was... (oops, wrong story )

But seriously... When IBM set up the Original IBM Personal Computer, that's how they laid things out on a desktop case. The same basic configuration was continued. It's not required that it work that way, but with the current setup, the cpu is close by the power supply, so that a lower fan on the power supply can pull the air right over the CPU. Many systems had air ducting doing just that - even in the Penium 2 days with passive heatsinks.

Not knowing that much about airflow etc., it seems like that would work, I'm not sure about adequate airflow for cooling though. However (and these aren't necessarily bad, just considerations):

1) Your mobo would have to be on the left side of the case instead of the right. You could also put the expansion slots to the front, with the mobo on the right then.

2) With the mobo 'upside down', be sure your PS has cables long enough to stretch to the bottom of the case (unless you're going to commission a custom mobo - rather an expensive proposition IMO). Same with floppy IDE/SATA cables

3) You would be cooling the rest of your system with air that already had cooled the 2nd hottest component in your system (assuming you have a newer-class video card).

4) Hmmm... can't think of a 4.

Mike.

 

[jcarte01]

in response to points
1) i'm building the pc into either the left or right handside of a press so with cpu high it would be mounted on the right with cpu low it would be mounted on the left, pci slots would always be rear facing.
2) length of cables, good point. thats a deciding factor really. going with a Abit KV8Pro V1.1 Mainboard Socket 754 K8T800PRO because it has toslink in and out (htpc btw) the 20 pin connector is about half way up one side so thats the same either way. the floppy will be internal if i install one at all. dvd drive will be as high as possible (less bending for me ) id like to keep the hard drive as low as possible may be in one of those 5.25 al cases to sush it a bit but when it comes down to it it will go where it has to.
3) another good point but the room is usualy 20c or less (north facing here in Ireland) entry level graphics card (once it has an s video connector for the TV) may put a thermometer in there for a few hours to see if an extra fan is needed.

cpu heat traveling up/down the motherboard is my main concern.

Homer: There’s 3 ways to do things, the right way, the wrong way, and the max power way.
Bart: isn’t that the wrong way.
Homer: yea but faster.