1) POWER SUPPLY:

The power supply is the weakest component in your computer!  In order to keep a computer running properly, you need a power supply that is appropriate for use with the system in which it is installed.  Too small or too big and it will either burn up or it won't supply enough "clean" power to keep your system running smoothly.

LOOK AT THE OLD POWER SUPPLY BEFORE YOU BUY A NEW ONE!  Be aware that all ATX power supplies do not put out all the required voltages for older motherboards.  Some ATX 2.0 power supplies are missing the minus 5-volt line on the 20-pin connector.  READ THE NEW POWER SUPPLY LABEL VERY CAREFULLY!!!  Make sure all the voltages necessary for your motherboard are available.  Check your motherboard manual for the required voltage specifications.

USE AN UNINTERRUPTIBLE POWER SUPPLY (UPS) AT ALL TIMES!  This important add-on prevents rapid switching on and off of the line voltage, which will damage the large primary capacitors inside the power supply (metal fatigue).  The internal welds of the capacitor "plates" will flex and break if the power is recycled too often.  When you turn off the power to your computer, WAIT A MINIMUM OF 15 SECONDS BEFORE TURNING  THE COMPUTER BACK ON!

My recent experience illustrates the problem of installing too big of a power supply.

I have been a hardware/software computer engineer for over thirty years and I could kick myself for forgetting the basics.  Power supplies weaken as they age and I forgot this property when recently troubleshooting an intermittently resetting, 800 MHz PIII back-up computer system.  For two weeks I thought it was a virus or spyware that was affecting my system.  After reloading the operating system three times and running all the antiviral and anti-spyware programs I have available, I finally decided it was either bad capacitors on the motherboard not supplying clean power to the CPU or, the power supply was dropping out intermittently.  The power supply change was the easiest to try first.

The next decision was which power supply should I substitute in place of the suspect unit?  The original was a 235-watt Fortron/Source ATX power supply.  I didn't want to substitute another used unit so, I went out and bought a new Suntec ATX-430 power supply at the local computer store.

After I installed the power supply and powered up the computer, I heard a constant, very high pitch squeal that quickly gave me a headache.  The problem is that the light load of my old system causes the hefty power supply to slow down the ultrasonic switching frequency into the upper audible range.  This is not how it is designed to work.  I had to change the supply until such time as I need more power in the system.  It did cause the intermittent resets to stop and I am happy I finally found the problem.

Some of the many things I like about the 430-watt Suntec unit is having the dual exhaust fans that are thermostatically controlled and the fact that over current as well as over voltage protection is provided on all voltages supplied.

My recommendations are not larger than a 350 watt power supply in an older computer system and a 500 watt or larger power supply (as large as you can afford) in a newer and faster, high power computer system.

2) COMPUTER CASE:

The laws of  physics tell us that heat generally rises so, it is best to have cooling air enter the case near the bottom (front) and exit near the top (rear).  This provides an environment that does not fight the natural flow of the unwanted heat and provides the maximum cooling possible.  If cables or other obstructions are in the way, the system can overheat so, be careful with lead dress.

Other configurations (down flow cases) may sometimes appear to work better but, then you are fighting the normal thermal physics of the system.  In any case, just make sure an exhaust fan is mounted at the top (rear) of the case and you can't go wrong.

One thing people forget is to force the air into the case.  If possible, mount a small fan (with an input air filter) blowing inward near the bottom of the case and let the air in!  If another fan is desired, I recommend mounting an exhaust fan on the back panel, just under the power supply.

WARNING: TOO MUCH AIR IS JUST AS BAD AS NOT ENOUGH AIR!!!  This may seem contrary to common sense but, it is a fact proven by both a detailed physics analysis of the situation and real world applications.

Do not use a fan that blows considerably more air than the case was originally designed to move by the manufacturer.  I did this years ago with a Pentium III and ended up not cooling the CPU chip enough.  It burned up in three weeks.  I then had to replace the CPU and install a proper cooling system.  When too much air is introduced in ANY cooling system, there is not enough time for the air to absorb the heat and then move it away from critical components!  The air just bounces off the hot item(s) and moves out of range without taking the excess heat with it.

NEVER PUT A LAPTOP FLAT ON A BED!!!  The sheets and blankets conform to the case and block the cooling holes on the bottom.  The internal parts are very densely packed and generate a lot of heat.  Cooling of a laptop is critical to extending the computer's life!

CLEAN YOUR SYSTEM CASE  FREQUENTLY!!!  Use a vacuum cleaner hose (on your closed case, not inside) to suck all the dust out of the exposed holes of your computer case, at least every two to four months.  If you let the dust and dirt build up, your computer will not breathe and cool properly.  The system will cook and die an unnecessarily early death.

Consider using a hard disk fan/cooler if your system case gets warm and always leave at least 2"of space on the desk around the case.  Mounting a disk drive above a hot power supply is an absolute no-no!  (I'm sorry to say, "Been there, done that, will not do it again!")

ATTENTION!!!  >>>  DO NOT PUT A COMPUTER ON THE FLOOR!  I cannot stress this important point enough!  I recieve more requests than I can handle to look at friend's computer systems that were put on the floor.  Dust and dirt easily enter the case in that position and have ruined more systems than I care to know about.  Rugs make this situation even worse!  Make sure your computer is at least 12" off the floor or inside a properly vented computer desk.  If in doubt, make some more holes (both high and low) in the back of the desk and consider adding a fan!  A friend of mine fried his system because he didn't have enough airflow inside his enclosed computer desk cabinet.

Don't forget to keep the video card cool!  The latest batches of ultra-VGA cards get HOT! HOT! HOT!  Put the video card in the highest physical slot in the system, mount a good fan/heatsink on the video chip, and keep airflow unobstructed around the card.  To help cooling, space plug-in cards as far apart as possible to ease airflow restrictions.  Remember, dead air pockets will not cool your system so, keep your cables neat!

Conclusion:

I recommend an approximately 17" to 18" high mid-tower case with the power supply at the top and no extra holes on the back that are not closed when you buy it.  Punch-outs are ok but, completely open holes that are not used immediately are a no-no.  They interfere with smooth airflow and therefor thwart proper cooling of the computer system.  Micro-tower cases and "bricks" do not hold enough air volume to properly cool a desktop computer system.  Avoid them like the plague!

My personal ideal case has four 5.25" exposed bays, two 3.5" exposed bays, and two hidden 3.5" bays, with two USB ports in the front and two USB ports in the rear.  In addition, there is provision for an intake fan at the front-bottom of the case and the power supply mounts at the very top of the case (rear).  On the back there is a spot earmarked for an additional 3.5" exhaust fan immediately below the power supply with no extra open holes of any kind.  It took me almost  a year of casual looking to find such a box.


3) Good luck with your next computer system build!  KEEP IT COOL!!!