"At the midpoint on the journey of life, I found myself in a dark forest, for the clear path was lost..." -Dante Alighieri
since it involves fans and cooling:
in short, you would generally want negative pressure to suck the heat out.
not sure if it would belong under fans or it's own article.
This is an area I've studied for years, and as personal computing & gaming require more and more intense machines, the heat requirements also increase in such compacted spaces.
Older PC's had a power supply fan and that cooled the entire unit. If you were running high end equipment, you might have an intake fan. This is a perfect example of a negative pressure system. The fan just sucks air out of the case and intakes it at specific points to control the air path.
Not much engineering or time was put into case manufacturing to make this efficient, as it was at best an afterthought and not necessary.
Then processors took off and it was realized that simply a passive cooling aluminum hunk wasn't cutting the mustard anymore. Most heatsinks utilized 40mm-70mm basic ball bearing fans and continued to use the aluminum heatsink. This didn't change much of the pressurization of the case, just provided a little extra air movement over a single hot component.
Then computing really took off. Video cards, front side bus, dual (or even triple) fans in power supplies, over hard drives, on everything.
The first few generations of these cases were just slap happy about throwing the standard 80mm fan into any space they viably could.
This time period showed just how loud 4-10 80mm fans could be. It was loud, but it seemed to work.
The focus towards case design was starting to look at airflow in a serious manner, but wasn't there just yet. Most cases of this generation were positive pressure machines, pushing air through the case with little regard to dust, or how to remove the higher quantities of hot air.
That's where fan case modding came to light in a mainstream way. Many PC nuts out there thought, "If they can do it, why can't I?"
Putting blowholes in the top of the case to expend the extra hot air, putting massive fans as outtakes to recapture a negative pressure system, and so on.
The market and case manufacturers caught onto this trend and realized that stock 80mm cooling just doesn't cut it. On top of style improvements, screwless designs(some of which were astonishingly pitiful), the design of airflow when creating cases came into question.
Between the failed motherboard standard BTX, which was supposed to provide better cooling solutions, the engineering and design of bigger, quieter fans in sleek cases, the ability for the home modder to take something that was made well and make it better, and the industry finally crawling into mainstream understanding of the beauty of the PC as an every-home appliance, many people are catching on to the new cooling solutions available.
Ranging from 25mm to 360mm, fans come in all shapes and sizes (and speeds).
A good rule of thumb is to look at the CFM(Cubic Feet per Minute). The higher this is, the more air pushes.
If noise is a concern for you, most fans also offer a decibel(dB) rating. The higher this number, the louder the fan.
Typically, larger fans produce more air and less noise. Many case manufacturers these days are putting 120mm fans as both intake and exhaust, due to cheap price, easy availability and the extreme amount of cooling that comes with a relatively low dB rating.
Now that the history lesson is over, the next post I'll drop on this subject will be about the pros & cons of negative vs positive pressure setups. But first, lunch.