Hi!

As far as air flow: IIRC, AT supply fans *exhausted* air from the supply;
while ATX fans 'suck.' I don't know if that's a hard & fast rule, but I
seem to recall the above as one of the changes when the ATX standard took
effect.

Every "regular" sized ATX supply I've ever seen pushes air out the back with
a fan mounted in the back of the supply, just like AT units have done for
years. It is usually the oddball sized or really cheap models that seem to
do things differently. Some ATX PSUs even seem to have fans at both ends,
which strikes me as odd.

If you have the technical chops, you can easily reverse the airflow by
opening the p.s. and turning the fan around. If your CPU has no fan, by
all
means get one. If you are 'really' concerned about airflow within the
enclosure, buy an auxiliary case fan--orienting it so that the airflow
supports that of the p.s. fan. Every case with which I'm familiar already
has a cutout with screw holes for one. Any computer store, electronics
supply store or even Radio Shack carries these.

My question is why do almost all computer manufacturers today bother putting
these holes in place? Some (like HP) use them and put a fan there, but many
do not. Most of them are even left open. I've only seen them closed up on
Gateway 2000 computers. I find that especially odd considering that the hole
for the extra fan is usually right under the PSU...which makes me think that
all the air comes in that hole and not necessarily through the case as it
should.