When it comes to cases, size is often inversely proportional to capability: for example, it would be rather difficult to stick two dual-slot-thickness graphics cards into a case that only had two slots - even if marketing departments might try to get you to believe otherwise. In the spirit of manipulative marketing, let's take a look at a few case sizes and see where they best fit.
|ATX Form Factor Case Size Guidelines|
|Typical Attributes||Full Tower||Mid Tower||Mini Tower||SFF Cube||Desktop|
|Height||20-24 inches||17-18 inches||13-14 inches||7-9 inches||3-7 inches|
|Width||6-8 inches||6-8 inches||6-8 inches||8-9 inches||14-17 inches|
|3.5" internal bays||6-12||2-6||1-2||1-2||1-4|
|Power supply||PS/2 or larger||PS/2||PS/2 or SFX||SFX or TFX||Various|
Remember that these are typical attributes, and not all cases are typical.
Full Towers are often nothing more than a mid-tower with an extended upper portion. While these have space for up to twice as many drives, the average user - and even most power users - simply won't need the space. A better excuse for the home user to select such a large case is that the upper bays are easier to reach when the unit is positioned on the floor.
ATX Mid-Towers are usually capable of holding full-sized motherboards, full-sized power supplies, several optical drives such as DVD burners, and multiple hard drives. They are best suited for gaming and video enthusiasts, simply because they support a greater number of expansion cards and hard drives than smaller units. Our recent Gaming Case Showdown describes a few contenders.
Micro ATX Mini-Towers are nearly as versatile as mid-towers in most applications, including office use, where they present a less imposing profile. Mini-Towers typically support 1-2 optical drives and 1-2 hard drives, and Micro-ATX supports a maximum of four expansion slots - all of these limitations are acceptable for most users. On the other hand, SLI-capable motherboards to fit these cases are scarce, and Crossfire-capable versions don't exist at all; this presents somewhat of a problem for high-performance graphics enthusiasts.
Small Form Factor (originally known as Shuttle Form Factor) cubes typically support a maximum of two expansion cards and only the smallest power supplies. Relying mostly on onboard devices, these space-saving enclosures are best suited to traditional office roles, though several have been designed for home theater use by mimicking the appearance of miniature hi-fi audio systems.
A variation based on SFF aesthetics is the Micro ATX cube. Often chosen for portable game machines, the small dimensions again mean restrictions on any attempt at an ultimate performance build. There are still Micro ATX slot limitations, full sized power supplies are a tight squeeze even when they do fit, and extended-length high-wattage units are out of the question.
Formerly used to raise small monitors up to eye level on flat desks, horizontal Desktop cases are now best suited to home theater systems. These come in a variety of shapes, sizes, and form factors to match most home theater rack components. Watch out for custom-sized power supplies that may not be upgradeable; horizontal card slots that might require a motherboard with slots to match specific riser types and locations; and half-height slots that severely restrict card selection.
Further selection criteria can be found in a variety of online case selection articles. Once you've got an idea of what size you need, Tom's Hardware Guide Case Reviews can point out the good and bad concerning specific models.