Your Computer's Case (continued...)

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.

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