Your computer's case plays a large part inthe overall expandability, protection, cooling and lifetime of your system.
Expandability
Atone time or another you may decide to add something to your computer. Maybe aCD Player, Zip Drive, a second Hard Drive, Floppy or Tape Drive. These fit onshelves in your computer called Bays. If there are no extra bays, then there’sno place for these devices to go. These bays can be 3.5 inches or 5.25 incheswide. There are internal and external bays. You can notice the externalbays by looking at the front of your case.
Devices like floppy drives and CD-ROMsslide into external bays and can be seen (and accessed) from the front of yoursystem case. If you have unused bays, they will have a plastic faceplate overthem (or at least they should have). If you see that you have empty externalbays, then you know that at least there's room to add another of this type ofdevice. Remember however, that hard drives are sometimes hidden behind thesefaceplates, so a look inside the case will tell you for sure. Hard drives aregenerally situated in internal bays because there is no need for physicaloutside access. You must look inside the case to see if you have any free internalexpansion bays.
Any device added to your system requirespower, and your power supply has to have enough juice to supply that power. Ifyou have a 150 or 200-watt power supply, your system may be limited to theamount of devices that can be added. Most cases come with a power supply, butmake sure.
Getting Your Hands in There
Youmay at one time or another, have to remove, change or check a device in yourcomputer. You want to be able to access that device without too muchdifficulty. It would be nice if you didn't have to remove the ribbon cables andexpansion cards just to install another DIMM, or replace a battery. Or, ifyou're the type that likes to just jam his hand in amongst all that stuff, itwould be nice to be able to remove it without accidentally loosening orremoving other connections.
On some cases you can loosen a singlescrew, and completely remove the drive bays for easy access to the drives andtheir mounting screws. Others have access ports for the screws on the back plateof the case. However, I’ve seen some drive bays that are spot-welded in placewithout access ports, and you just about have to remove the motherboard toaccess the screws for the drives. Think about what you want to put inside andmake sure there's enough room for access.
Protection
Agood, rigid, well built case can protect the internal components from dust,vibration, foreign objects, ESD and EMI. Electromagnetic interference is notalways an easy one to nail down. My computer has a good solid case, but whenyou watch TV, you can tell if the computer is on or not.
You can find cheap cases that fit togetherso poorly, or are so flimsy, that they actually rattle when the computer isturned on. One thing that can be bad for your system are vibrations caused byoutside sources; whether it’s a panel or cover that rattles, a desk drawerbeing closed, or a printer that doesn’t operate the smoothest. The stability ofthe case makes a big difference.
Some of the case frames are leftunfinished, resulting in sharp edges, burrs and metal slivers. Ribbon cablesand wires (and your fingers) can be nicked or cut by these sharp edges just byremoving or replacing the outside cover. Companies that actually put someresearch and development into their product will address these issues. Youshould think about them when you purchase. As with just about everything, youusually get what you pay for.
Longevity
Heatshortens the life of electronic components.Thedifferent devices and components inside your case need room to breathe andrelease heat build-up. Sometimes, things are packed so tightly inside yoursystem case that you can’t even get your hand in to remove a cable or anexpansion card, let alone allow for any kind of air flow. Air flow is needed tocool down the components and devices inside the case.
The cooler that your computer operates, thelonger it will last. The fan on the power supply is made to help cool the powersupply as it operates. The way the case is built should allow the intake ofcooler air through vents, draw it over the different components inside to helpcool them, and push the heated air out. Some cases come with auxiliary fansthat fit over the intake vents to add to the airflow inside.
It’s important not to interrupt this flow.Don’t pack things around the case or obstruct the intake vents. Keep the intakevents clean and clear of grime and dust balls. Also, by leaving the expansionslot inserts off the back of the case, or the faceplate off unused externalbays, you could possibly be changing the way the air flows through your caseand reducing cooling efficiency.
If you have a system that seems to runfine, then just shuts itself off after a half hour or so, check out theoperating temperature of the CPU. See that the fans are working on the powersupply and the CPU's heatsink.
Switches and LEDs
If you look at the front of your case you can see the devices that areinstalled in the external bays and get an idea as to how many unused bays youhave. You will also notice one or more switches and LED lights.
Power switch
To start your computer, you have to turn on the power supply. At one time, thepower switch for your computer was on the power supply itself, and you had toreach around to the back of your computer to turn it on and off. This wasinconvenient, troublesome, and a real pain in the …neck. Most cases today havea remote power switch on the front of the case.
Reset switch
When you first start your computer, it goes through a series of self-tests(POST - Power-On Self Test) before it actually initializes itself and starts upthe operating system. The reset switch performs the same function as a warmboot (ctrl+alt+del) which restarts your computer with an abbreviated version ofPOST, taking a little time off the startup process. With Win95/98’s restartoption on the Start menu, today’s computer cases may or may not have a resetswitch.
Turbo switch
When computer speeds started to increase dramatically, older software programssometimes worked too fast. This was especially noticeable in games. By pushingthe Turbo switch, you could slow the speed down to where these programs werestill usable. This also became the number one cause for a lot of trouble callsfrom people complaining that their computer "just doesn’t work as fast asit used to". Most cases today don’t have a Turbo switch.
Keylock switch
Most new cases don’t have a Keylock switch. By inserting and turning a key inthis lock, you could shut off access to the keyboard, thus denying unwantedusers from accessing your computer or preventing an accidental keystroke frominterfering or interrupting a currently active program. These are still foundon network servers.
Power LED
This light tells you when the power is on to your computer.
Hard Drive LED
This light will go on, or flicker, every time your hard drive is written to orread from. It lets you know whenever the hard drive is being accessed.
Turbo LED
Not found on newer cases, the Turbo light would tell you when the Turbo switchhad been pushed.
Speed LED
The Speed Indicator LED is supposed to indicate the speed (in megahertz) thatyour computer runs. The problem is, they don’t actually read the speed. TheseLEDs have to be set using an array of jumpers in the front panel of the case.If you change the speed of your computer, these indicators won’t change unlessyou physically change the jumpers. Unless you have the instructions (casesdon’t always come with instructions), you don’t have much of a chance atguessing the jumper configuration. There’s getting to be fewer and fewercomputer cases with Speed Indicator LEDs.
Eachdevice installed in a case’s external drive bay (floppy drive, CD-ROM, tapedrive, etc.) will usually have it’s own indicator LED on the front bezel thatwill come on or flicker when that device is being accessed.
The back of your computer will have holes and slots cut into the frame. Theseholes allow for the back of expansion cards and any I/O ports that yourexternal devices can plug into. Any slot or hole that is empty should have acover on it. These are easy to distinguish from any venting holes that might beon the back of your case (venting holes should not be covered). The back of thepower supply will also be exposed here showing you the power supply fan ventand the plug for the power cord.
Case Styles
Basically,there are two different styles of system cases today. The Desktop and the Tower.
The desktopcase sits flat on the top of your desk with the monitor situated on top. Thiswas the style of IBM's original PC, XT and AT models. These early desktops werefairly large and bulky, taking up a lot of real estate on the desk. The obvioustrend was formanufacturers to make them smaller and more compact. Unfortunately, as you makethe case smaller, things inside get a little crowded. Access to the differentcomponents becomes much more cramped, cooling is a lot less efficient,and there's less room for expansion. Desktops usually have two or threeexternal drive bays and 1 or 2 internal bays.
The slimline case iseven smaller. It's shorter, narrower, andlooksa lot less bulky on your desk. This is about the only appeal these machines mayhave. Slimline computers are very proprietary, not well cooled at all, and haveabout zero room for expansion. Slimlines usually have one or two external baysand one internal.
The tower case sits onend, taking up less square area space and offering a better variety of sizesthan a desktop. It allows for a lot more choice as to location, depending ofcourse on the particular size. It can sit on the desk beside the monitor,on a separate shelf, or on the floor beside the desk. On the negative side, itshould be mentioned that cases on the floor may be more prone to kicks and bumpsand in some locations, the cords may have to be extended. Tower cases have muchbetter air flow, better accessability to internal components, and (except forthe micros and ultra low end models) allow for more upgrade and expansioncapability.
Full Tower
-largest, up to 36" high
-sits on floor
-larger power supplies, 350 watts or more
-may have 2 X 3.5" and 4 or more 5.25" external bays
-may have 4 or more internal drive bays
-very roomy inside. Better cooling
-most expensive
Mid Tower
-power supply - 200 - 300 watts
-quite popular size
-approx 17-20 inches in height
-2 X 3.5" and 3 X 5.25"external drive bays
-2 or 3 internal drive bays
-less room than a full tower to work inside
-still cools really well
-still room for expansion
Mini Tower
-very popular size
-smallest of the tower cases (...sub-mini and micro?)
-can be less than 14 inches high
-power supply 200 to 250 watts
-cools better than a desktop case (but not much)
-2 X 3.5" and 2 X 5.25" external drive bays
-1 or 2 internal drive bays
-a little cramped inside
Note: The sub-mini and micro size cases areactually smaller than the mini tower. These cases have 1 or 2 external drivebays and only 1 internal bay. The sub-mini and micro are targeted at the lowend computer market and usually have very limited possibility for upgrade andno room for expansion.
Remember too, that there can be some prettyfine lines between the different case styles. One company's mid-tower might beanother company's midi-tower. One might take out a single 5-1/4" bay, andcall it a mini-tower, whereas the next manufacturer may still refer to it as amid-tower.
Form Factors
Form Factors
Cases come in different sizes and styles, and so do motherboards. The size andshape of the circuit board, the position of the components, the position of thescrew holes, and the technology incorporated make up a motherboard’s formfactor. If you buy a new computer, it’s not really a problem, the system boardis already in the case. But, if you're building a computer, or buying a new casefor a computer, then you have to be sure the case will accomodate themotherboard’s form factor. The case gets its form factor name based on the formfactor of the motherboard that it will accomodate.
The PC/XT was the original formfactor introduced by IBM. It only came in desktop form and, though it lookedpretty high-tech and streamlined at the time, was fairly large and clunky.They're not made anymore, they were replaced by the AT form factor.
Because technology had advanced somewhat,components were becoming smaller (the evolution continues to this day).Components on the AT motherboard were positioned a little moreefficiently, and the size of the power supply was reduced without any loss inperformance. The position of the power supply also changed with theintroduction of the tower-style case. Now you could get two different styles ofcase, the desktop and the tower, with some variation in sizes, as well.
Cooling became much more efficient, withthe power supply fan blowing air out the top, and the vent holes near thebottom of the case allowing cooler air to be sucked in. The AT formfactor also moved the power switch from the back, or side, to the front of thecase (remote power switch). The AT is also not available anymore.
With components becoming increasinglysmaller, voltages changing, and chip and component placement becoming moreefficient, manufacturers discovered they could make the board smaller. Theydecreased the width of the AT form factor and introduced the Baby AT.The fact that less material was required to manufacture it, and theintroduction of IDE connectors, and other I/O connectors that are integrateddirectly on to the motherboard, resulted in cheaper production costs. This madethe new form factor quite popular with the manufacturer.
The case that conformed to the Baby AT formfactor could now become slightly smaller in stature. That made the Baby ATform factor quite popular with the consumer.
Most of the computers above the Pentium MMXhave gone away from the Baby AT format, to the ATX. But as long asthe Pentiums 200 - 266 remain a useful and plentiful machine, the Baby AT formfactor wtill probably remain available.
Thecomponent configuration on the ATX motherboard is fairly similar to theBaby AT. By taking the Baby AT and turning it 90 degrees, the CPU and memorymodules become more easily accessible. The Baby AT introduced integrated I/Oconnectors that attached, via small ribbon cables, to the ports installed onslot-plates at the back of the computer. With The ATX, integration istaken one step further. The different serial, parallel, and USB ports arehardwired directly to the motherboard in a small cluster at the back of thecomputer.
Thepower supply connector has changed a bit also. P8 and P9 connectors have beenreplaced by a single tabbed connector. The remote switch on the ATX isconnected to the motherboard, not directly to the power supply, and there ispower to the board at all times. The cases come in all the regular sizes andstyles. The ATX is currently the most popular form factor out there.
Thereis a slightly smaller version of the ATX called the Mini ATX. Althoughthe motherboard is slightly more compact, it uses the same case and powersupply. I mention it here, only to differentiate between it, and the Micro ATX.
Themore compact version of the ATX is called the Micro ATX, and it'stargeted toward the low end computer market. The cases generally have about 1 X5-1/4" bay, 1 X 3.5", and 1 internal bay. The Micro ATX power supplyis also smaller, and usually has just enough power for what's already in thecomputer. There is very little (zero) room for expansion. I think the Micro ATXprobably came about as a result of manufacturers competing for that first'under $1000' computer.
Thereis another case and MB combination, the NLX, that may become morepopular than the ATX. Mostly due to the fact that the big name manufacturersuse the NLX form factor extensively to mass produce systems at a reducedcost. The NLX has a single expansion slot on the motherboard. There's ariser card that fits into the slot and contains the rest of the expansion slotsrequired by the system. The whole idea is to be able to make the case narrower,and it does the job. The case is no longer limited by the height of the expansioncards because the expansion cards are installed horizontally. Although NLXis a recognized standard, and the parts are supposed to be interchangeable,they still seem to be quite proprietary. You'll recognize the NLX by thehorizontal slot holes at the back of your computer.