Your Computer’s Case

Your computer's case plays a large part in the overall expandability, protection, cooling and lifetime of your system.

Expandability

At one time or another you may decide to add something to your computer. Maybe a CD Player, Zip Drive, a second Hard Drive, Floppy or Tape Drive. These fit on shelves in your computer called Bays. If there are no extra bays, then there’s no place for these devices to go. These bays can be 3.5 inches or 5.25 inches wide. There are internal and external bays. You  can notice the external bays by looking at the front of your case.

Devices like floppy drives and CD-ROMs slide into external bays and can be seen (and accessed) from the front of your system case. If you have unused bays, they will have a plastic faceplate over them (or at least they should have). If you see that you have empty external bays, then you know that at least there's room to add another of this type of device. Remember however, that hard drives are sometimes hidden behind these faceplates, so a look inside the case will tell you for sure. Hard drives are generally situated in internal bays because there is no need for physical outside access. You must look inside the case to see if you have any free internal expansion bays.

Any device added to your system requires power, and your power supply has to have enough juice to supply that power. If you have a 150 or 200-watt power supply, your system may be limited to the amount of devices that can be added. Most cases come with a power supply, but make sure.

Getting Your Hands in There

You may at one time or another, have to remove, change or check a device in your computer. You want to be able to access that device without too much difficulty. It would be nice if you didn't have to remove the ribbon cables and expansion cards just to install another DIMM, or replace a battery. Or, if you're the type that likes to just jam his hand in amongst all that stuff, it would be nice to be able to remove it without accidentally loosening or removing other connections.

On some cases you can loosen a single screw, and completely remove the drive bays for easy access to the drives and their mounting screws. Others have access ports for the screws on the back plate of the case. However, I’ve seen some drive bays that are spot-welded in place without access ports, and you just about have to remove the motherboard to access the screws for the drives. Think about what you want to put inside and make sure there's enough room for access.

Protection

A good, rigid, well built case can protect the internal components from dust, vibration, foreign objects, ESD and EMI. Electromagnetic interference is not always an easy one to nail down. My computer has a good solid case, but when you watch TV, you can tell if the computer is on or not.

You can find cheap cases that fit together so poorly, or are so flimsy, that they actually rattle when the computer is turned on. One thing that can be bad for your system are vibrations caused by outside sources; whether it’s a panel or cover that rattles, a desk drawer being closed, or a printer that doesn’t operate the smoothest. The stability of the case makes a big difference.

Some of the case frames are left unfinished, resulting in sharp edges, burrs and metal slivers. Ribbon cables and wires (and your fingers) can be nicked or cut by these sharp edges just by removing or replacing the outside cover. Companies that actually put some research and development into their product will address these issues. You should think about them when you purchase. As with just about everything, you usually get what you pay for.

Longevity

Heat shortens the life of electronic components. The different devices and components inside your case need room to breathe and release heat build-up. Sometimes, things are packed so tightly inside your system case that you can’t even get your hand in to remove a cable or an expansion card, let alone allow for any kind of air flow. Air flow is needed to cool down the components and devices inside the case.

The cooler that your computer operates, the longer it will last. The fan on the power supply is made to help cool the power supply as it operates. The way the case is built should allow the intake of cooler air through vents, draw it over the different components inside to help cool them, and push the heated air out. Some cases come with auxiliary fans that 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 intake vents clean and clear of grime and dust balls. Also, by leaving the expansion slot inserts off the back of the case, or the faceplate off unused external bays, you could possibly be changing the way the air flows through your case and reducing cooling efficiency.

If you have a system that seems to run fine, then just shuts itself off after a half hour or so, check out the operating temperature of the CPU. See that the fans are working on the power supply and the CPU's heatsink.

Switches and LEDs

If you look at the front of your case you can see the devices that are installed in the external bays and get an idea as to how many unused bays you have. 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, the power switch for your computer was on the power supply itself, and you had to reach around to the back of your computer to turn it on and off. This was inconvenient, troublesome, and a real pain in the …neck. Most cases today have a 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 up the operating system. The reset switch performs the same function as a warm boot (ctrl+alt+del) which restarts your computer with an abbreviated version of POST, taking a little time off the startup process. With Win95/98’s restart option on the Start menu, today’s computer cases may or may not have a reset switch.

Turbo switch

When computer speeds started to increase dramatically, older software programs sometimes worked too fast. This was especially noticeable in games. By pushing the Turbo switch, you could slow the speed down to where these programs were still usable. This also became the number one cause for a lot of trouble calls from people complaining that their computer "just doesn’t work as fast as it 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 in this lock, you could shut off access to the keyboard, thus denying unwanted users from accessing your computer or preventing an accidental keystroke from interfering or interrupting a currently active program. These are still found on 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 or read 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 switch had been pushed.

Speed LED

The Speed Indicator LED is supposed to indicate the speed (in megahertz) that your computer runs. The problem is, they don’t actually read the speed. These LEDs 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 unless you physically change the jumpers. Unless you have the instructions (cases don’t always come with instructions), you don’t have much of a chance at guessing the jumper configuration. There’s getting to be fewer and fewer computer cases with Speed Indicator LEDs.

   
Each device installed in a case’s external drive bay (floppy drive, CD-ROM, tape drive, etc.) will usually have it’s own indicator LED on the front bezel that will come on or flicker when that device is being accessed.

The back of your computer will have holes and slots cut into the frame. These holes allow for the back of expansion cards and any I/O ports that your external devices can plug into. Any slot or hole that is empty should have a cover on it. These are easy to distinguish from any venting holes that might be on the back of your case (venting holes should not be covered). The back of the power supply will also be exposed here showing you the power supply fan vent and the plug for the power cord.

Case Styles

Basically, there are two different styles of system cases today. The Desktop and the Tower.

The desktop case sits flat on the top of your desk with the monitor situated on top. This was the style of IBM's original PC, XT and AT models. These early desktops were fairly large and bulky, taking up a lot of real estate on the desk. The obvious trend was for manufacturers to make them smaller and more compact. Unfortunately, as you make the case smaller, things inside get a little crowded. Access to the different components becomes much more cramped, cooling  is a lot less efficient, and there's less room for expansion. Desktops usually have two or three external drive bays and 1 or 2 internal bays. 

The slimline case is even smaller. It's shorter, narrower, and looks a lot less bulky on your desk. This is about the only appeal these machines may have. Slimline computers are very proprietary, not well cooled at all, and have about zero room for expansion. Slimlines usually have one or two external bays and one internal.

The tower case sits on end, taking up less square area space and offering a better variety of sizes than a desktop. It allows for a lot more choice as to location, depending of course 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, it should be mentioned that cases on the floor may be more prone to kicks and bumps and in some locations, the cords may have to be extended. Tower cases have much better air flow, better accessability to internal components, and (except for the micros and ultra low end  models) allow for more upgrade and expansion capability. 

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 are actually smaller than the mini tower. These cases have 1 or 2 external drive bays and only 1 internal bay. The sub-mini and micro are targeted at the low end computer market and usually have very limited possibility for upgrade and no room for expansion.

Remember too, that there can be some pretty fine lines between the different case styles. One company's mid-tower might be another company's midi-tower. One might take out a single 5-1/4" bay, and call it a mini-tower, whereas the next manufacturer may still refer to it as a mid-tower.



Form Factors

Cases come in different sizes and styles, and so do motherboards. The size and shape of the circuit board, the position of the components, the position of the screw holes, and the technology incorporated make up a motherboard’s form factor. If you buy a new computer, it’s not really a problem, the system board is already in the case. But, if you're building a computer, or buying a new case for a computer, then you have to be sure the case will accomodate the motherboard’s form factor. The case gets its form factor name based on the form factor of the motherboard that it will accomodate.

The PC/XT was the original form factor introduced by IBM. It only came in desktop form and, though it looked pretty 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 more efficiently, and the size of the power supply was reduced without any loss in performance. The position of the power supply also changed with the introduction of the tower-style case. Now you could get two different styles of case, the desktop and the tower, with some variation in sizes, as well.

Cooling became much more efficient, with the power supply fan blowing air out the top, and the vent holes near the bottom of the case allowing cooler air to be sucked in. The AT form factor also moved the power switch from the back, or side, to the front of the case (remote power switch). The AT is also not available anymore.

With components becoming increasingly smaller, voltages changing, and chip and component placement becoming more efficient, manufacturers discovered they could make the board smaller. They decreased the width of the AT form factor and introduced the Baby AT. The fact that less material was required to manufacture it, and the introduction of IDE connectors, and other I/O connectors that are integrated directly on to the motherboard, resulted in cheaper production costs. This made the new form factor quite popular with the manufacturer.

The case that conformed to the Baby AT form factor could now become slightly smaller in stature. That made the Baby AT form factor quite popular with the consumer.

Most of the computers above the Pentium MMX have gone away from the Baby AT format, to the ATX. But as long as the Pentiums 200 - 266 remain a useful and plentiful machine, the Baby AT form factor wtill probably remain available.

The component configuration on the ATX motherboard is fairly similar to the Baby AT. By taking the Baby AT and turning it 90 degrees, the CPU and memory modules become more easily accessible. The Baby AT introduced integrated I/O connectors that attached, via small ribbon cables, to the ports installed on slot-plates at the back of the computer. With The ATX, integration is taken one step further. The different serial, parallel, and USB ports are hardwired directly to the motherboard in a small cluster at the back of the computer.

The power supply connector has changed a bit also. P8 and P9 connectors have been replaced by a single tabbed connector. The remote switch on the ATX is connected to the motherboard, not directly to the power supply, and there is power to the board at all times. The cases come in all the regular sizes and styles. The ATX is currently the most popular form factor out there.

There is a slightly smaller version of the ATX called the Mini ATX. Although the motherboard is slightly more compact, it uses the same case and power supply. I mention it here, only to differentiate between it, and the Micro ATX.

The more compact version of the ATX is called the Micro ATX, and it's targeted toward the low end computer market. The cases generally have about 1 X 5-1/4" bay, 1 X 3.5", and 1 internal bay. The Micro ATX power supply is also smaller, and usually has just enough power for what's already in the computer. There is very little (zero) room for expansion. I think the Micro ATX probably came about as a result of manufacturers competing for that first 'under $1000' computer.

There is another case and MB combination, the NLX, that may become more popular than the ATX. Mostly due to the fact that the big name manufacturers use the NLX form factor extensively to mass produce systems at a reduced cost. The NLX has a single expansion slot on the motherboard. There's a riser card that fits into the slot and contains the rest of the expansion slots required 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 expansion cards because the expansion cards are installed horizontally. Although NLX is a recognized standard, and the parts are supposed to be interchangeable, they still seem to be quite proprietary. You'll recognize the NLX by the horizontal slot holes at the back of your computer.