They're just simple boxes, you say? On the contrary, PC cases are complicated. And we're just talking about buying one. (We'll leave actually building a working PC up to you.)
There's plenty of terminology to know when shopping for a new PC case, as you'll see in our list of specs and jargon below. Whether you're buying a case as an upgrade or for a build-a-PC-from-scratch project, we suspect you're savvy enough to take your PC to pieces and put it back together again. But when shopping, the terminology around cases and motherboards can be confusing, and some of it can stump even experienced builders.
First-time buyers and builders, meanwhile, definitely need to go into a purchase with a bit of background knowledge (or a savvy friend) to get a case that makes sense for the components they have.
Let us be that friend. Here's a primer on the language you'll hear buzzing around PC chassis from sellers and PC enthusiasts.
PC cases themselves are often referred to by these three form factors, but the terms more accurately refer to the size of the motherboards they can host. ATX boards measure 12 by 9.6 inches, MicroATX up to 9.6 by 9.6 inches (they're sometimes smaller), and Mini-ITX 6.7 inches square.
Broadly speaking, a case that supports a larger board will itself tend to be larger than one that supports only smaller boards, but this is not universally true. Also, note that a case that supports a given motherboard size likely supports the smaller motherboard form factors, too, although that's worth verifying in a case's specs before buying. Most ATX-compatible cases, for example, will accept a MicroATX or Mini-ITX board. (Of course, a big PC case holding a small motherboard may not be the best use of space!)
Though not exact terms, these are the five most common ones used to describe the shape and size of a given PC case. Small-form-factor (SFF) encompasses a variety of compact cases, some flat, some tall; most employ Mini-ITX or smaller proprietary motherboard designs. A desktop case, used specifically in the context of PC-case design (since the term encompasses "desktop PCs" as a whole, too), is one with a horizontal design, often intended to have a monitor placed atop it.
Conventional vertical desktop towers are mini-towers, mid-towers, or full towers, but the size distinctions among these are not exact. A full tower as described typically stands 18 inches tall or more.
This is marketing lingo that has become part of PC builders' vernacular. A "tool-free" design refers to parts of a PC case that don't require screws or a screwdriver to install. Drive bays might be referred to as tool-free, with a hardware design that uses twist-on or snap-on brackets or levers instead of screws to mount drives.
Tool-free fasteners on 5.25-inch bays in a Thermaltake chassis.
In some cases, the installation of expansion cards can be tool-free, as well, with levers or other mounting schemes that eliminate the need for screws to clamp a PCI or PCI Express card into the case's expansion slots. "Tool-free" might also refer to how a case's side panel is fastened to the chassis, using a lever or button as a release mechanism in place of screws.
A case will come with a bank of these, usually more the larger the case. A 5.25-inch bay is meant for use with an optical drive (such as a DVD burner or Blu-ray drive) and will match up with removable faceplates on the front of the case. (Some late-model cases have begun eliminating these "front-accessible" bays, as optical drives are falling out of favor.) In years past, these bays were also commonly used by PC builders and enthusiasts to host front-panel devices such as fan controllers or temperature readouts, or to install auxiliary panels that provide extra ports on the front of the PC. An SFF or minitower case may have as few as one of these bays, or none; a full tower usually up to four. The 5.25-inch and 3.5-inch bays are the ones likely to employ a tool-free design (see above).
Four 5.25-inch and one 3.5-inch bays on a Thermaltake case.
The 3.5-inch bays, meanwhile, are meant for the installation of platter-style hard drives. The 3.5-inch bays may be designed to accept 2.5-inch drives, as well. The bay may use drive sleds (see below), or you may screw the drive directly into the bay.
With the rise of solid-state drives (SSDs), 2.5-inch bays are now common. They tend to be implemented in whatever spare space the case has, since the drives are physically so small and thin. A few cases do provide dedicated 2.5-inch drive sleds, but in most designs that use drive sleds, you can screw a 2.5- or a 3.5-inch drive into the sled. But 2.5-inch bays may be stuck anywhere there is available space, sometimes even hidden behind the motherboard tray.
If you've ever assembled a PC from parts, you've probably cut your finger on one of these. The I/O shield is a rectangular metal plate (usually with sharp edges) that snaps into a rectangular gap on the back of your PC case. (The shield itself comes with your motherboard, not with the case you buy.) The shield will have cutouts for the specific ports on the motherboard, and installing the shield will protect the rest of the board when you insert various cables into the ports.
An I/O shield from an EVGA motherboard.
Generally speaking, I/O shields are not interchangeable between different motherboards. The only things standard about them are their overall dimensions, roughly 1.75 by 6.5 inches, which ensure that they'll fit in any PC case.
Many higher-end CPU coolers require a backing plate or other mounting hardware (such as some kind of pass-through bolt) that you install from underneath your motherboard. If your PC is already built and you want to swap CPU coolers (or get at the CPU for an upgrade), you may need access to the underside of the motherboard to get the CPU cooler on or off.
Closeup of the CPU cutaway on an NZXT case.
Removing a motherboard, of course, is usually a major task, given all the wiring and screws. With a CPU-cooler cutaway in the motherboard tray, you can swap CPU coolers and access the CPU without removing the motherboard. Most modern aftermarket cases, even cheap ones, have such a cutaway these days, but it's definitely a feature worth looking for.
In many chassis, the motherboard "tray"—the area on which a motherboard mounts—is simply the bottom of the chassis. It's usually patterned with holes for the motherboard standoffs, if the standoffs are not preinstalled.
A removable motherboard tray (with motherboard mounted) from a Lian-Li server chassis.
The term "tray" comes from a time when a premium feature in a PC case was actually a removable motherboard tray—a "second bottom," as it were, in the case that you could remove from the case altogether to mount and wire up the motherboard outside the chassis. Such trays aren't quite extinct, but they are far less common these days.
These are brass bits with a hexagonal top that usually come in a small bag with your PC case. You twist these into pre-drilled holes in the motherboard tray. You then screw your motherboard down on top of the standoffs, which act as "spacers" and keep the motherboard from touching the bottom of the case. (Thus, the name.)
The brass bits.
A PC chassis usually has notations next to the holes in the tray, pressed into the metal, that tell you which holes require a standoff for a given form factor of motherboard (ATX, MicroATX, and so on) that you might be installing. Some cases have the standoffs pre-installed, and a few have them molded or machined into the case bottom, but the norm is a baggie of these that you install yourself. An ordinary 5mm metric socket, if you own a socket set, can help you install these securely.
The PSU, or power supply unit, is the large box inside your PC's case that traffics electricity to the various components in your PC—drives, fans, and the motherboard itself—via its hydra-like leads. The PSU mounting area in tower cases will be at the top or bottom of the case. The supply usually mounts via four screws, through the back of the case. You'll see a telltale large cutaway at the back of the case where the power supply goes. (The cutaway is to allow the exhaust fan to ventilate out the back of the case.)
In terms of fit into a given PC chassis, most tower and moderate-size desktop chassis accept full-size, or ATX, power supplies (not to be confused with the ATX motherboard form factor). Some compact or SFF PC chassis require a smaller PSU form factor, known as SFX. Other small chassis require smaller, proprietary PSUs (which, typically, will come with the case). And in some modern cases with glass or acrylic sides, the PSU may be hidden under a "PSU shroud" (more on that in a moment).
These are surfaces inside a PC case that allow you to install an aftermarket cooling fan for additional interior ventilation. The most typical fan sizes used in PC cases are 80mm, 92mm, 120mm, 140mm, and 200mm, with 120mm and 140mm being the most common. You'll want to be sure, if you'll be adding fans, that the ones you buy match the size of the mount. The mount usually has screw holes predrilled in the chassis for the specific fan size, and a different fan size probably will not mount properly there.
Removable filter for a front fan mount on a Thermaltake chassis.
With some cases, the fan mount might have a removable, cleanable air filter covering the front face, if that fan would be used as an intake. Filters are a good feature to have, as they will help minimize the settling of dust inside your PC case.
Once the province only of premium/enthusiast PC cases, drive sleds have made their way into cases across the price spectrum. Used almost exclusively with the 3.5-inch bays in the case (and, in a few rare examples, in the 2.5-inch bays), drive sleds are metal or plastic frames that slide in or out of a drive bay. You screw or otherwise lock a drive into a sled, then slide the whole assembly into place in the bay.
Sample drive sled with mounting points for both 3.5- and 2.5-inch drives.
In some chassis, the drive sleds enable the drive to engage with a "backplane" that's part of the case. The backplane will have SATA data and power connectors built into it. This helps streamline wiring, and, depending on the implementation, may also make the drives hot-swappable.
You'll see this term used in both motherboard and PC-case contexts. A "header" on a motherboard is (in most implementations) a grid of pins that you plug a cable into, usually from a case fan, or from a port or button on the case itself. The most common type of motherboard headers are USB 2.0, USB 3.0, HD Audio (more on that in a bit), and four-pin fan headers.
From a PC case perspective, all cases will have "header cables" that run from its front ports, power/reset buttons, and LEDs. Each of these cables terminate in a female header connector of some kind. Each type is standard in implementation; for example, a USB 2.0 header cable will end in a five- or 10-pin connector (depending on whether it feeds one or two USB ports), while USB 3.0 always uses the same big 19/20-pin header connection.
Your average modern PC case will have header cables for USB 2.0, USB 3.0, and the front audio jacks, plus a small bouquet of header cables for the various front-panel switches (power, reset) and LEDs (hard drive activity, power-on). You'll want to be sure that the motherboard you're installing in the case has matching header connectors; in practical fact, though, this is only an issue with having the right number and kind of USB headers (or not). The rest are standard, nowadays.
A general term for various features inside a PC chassis that help you "clean up" the interior and improve airflow by making it easier to streamline or hide cables. Cable management encompasses everything from cutaways in the case bottom (which let you route cables behind the mainboard) to extra space behind the motherboard tray (for stuffing excess cable out of sight).
The soft-lined cable-management cutouts on an NZXT case.
Cable cutouts lined with rubber or other soft material to prevent wire chafing on sharp edges, as well as mounting points in the case for cable ties, are both good cable-management features to look for.
These specs, which some case makers will cite, are important to know if you intend to install a large, high-end video card or a tall, tower-style CPU cooler. They're measurements that will typically be given in millimeters or, less commonly, inches.
Graphics-card clearance, in a few cases, can be variable thanks to removable pieces of the case; some models that we have tested come with a removable bank or banks of hard drive trays that, if taken out, extend the space inside the case available to a long video card. A GPU clearance of more than 12 inches should accommodate almost any modern card, but look carefully if you happen to own a long video card that has the power connectors extending from the trailing edge, which can add to the effective length.
A recent development in PC-enthusiast cases is the "PSU shroud." You'll only see these in PC cases that have a transparent side-panel window. It's an enclosure inside the PC case, usually running along the top or bottom, that hides the entire PSU box (and most of its wiring) from view, for a neater internal appearance. Usually, the shroud will have cutaways or pass-throughs to allow some of the PSU cabling to enter the case.
This is a generic term for the ports that are part of a PC case, usually found on the front face of the chassis but, in some designs, on the top front or even down one of the sides, near the front. On most PC cases, you'll get headphone and mic jacks as part of this array, as well as some USB 3.0 or 2.0 ports (or both). Other ports you may see as parts of the front I/O panel in an older chassis are eSATA and FireWire; no new chassis released in recent years includes these, but bear these in mind if you're shopping eBay or used gear. You're looking at a classic chassis if it has one of these.
The headphone and mic jacks attach to a PC's motherboard via an HD Audio connector that comes as part of the case, while the USB ports will have different header cables depending on which kind they are (USB 3.0 versus 2.0). Almost all modern motherboards will include one (or less often, two) USB 3.0 headers and two or more USB 2.0 headers.
A few of the latest cases include a USB 3.1 Type-C port, which uses a new kind of USB 3.1 header connection to the motherboard that you'll see only on some 2017 or 2018 mainboards. You'll want to make sure that your PC motherboard has matching headers for the kinds of ports that your case has; otherwise, you'll have to tolerate dead "ports to nowhere" or buy esoteric adapters to get them to work.
In the context of PC cases, vendors often cite a number of "expansion slots" supported. They are actually just referring to the spacers in the back of the case, usually covered by removable strips of metal, onto which you mount the bracket of a PCI or PCI Express card.
The number of actual usable slots in a case, however, is contingent upon there being enough such slots on your motherboard. In practice, a chassis that supports a given form factor of motherboard will provide enough slot "positions" for the slots actually implemented on the motherboard.
These ports, which tended to show up on enthusiast-grade cases in years past, are found on the back of the case. They're actually holes, usually with a rubber or silicone rim, that let you install custom water-cooling hardware inside the case but mount the water-cooling system's radiator on the outside of the chassis. You'd route the inflow and outflow hoses out the back of the case through these ports.
To the right of the expansion slots on this Raidmax case are three water-cooling hose passthroughs.
Why would you want to do this? Most likely, it's because the case doesn't have enough room for a radiator inside on its fan-mounting points. Increasingly, though, makers of enthusiast PC cases design their cases to accommodate 120mm, 240mm, or 360mm radiators inside their chassis. Enthusiast cases might have these ports, but the increasing popularity of all-in-one (AIO) water-cooling solutions has meant that these ports are of marginal interest nowadays, and that only to the hardest of hard-core PC builders and tweakers, who might be constructing elaborate liquid-cooling arrangements that involve some external component.
No, not the medieval kind: These are the chunky screws used in many PC cases that hold in place case side panels, expansion cards, or other hardware.
A finger-friendly bundle of thumbscrews.
In theory, you can add and remove them without a screwdriver. In practice, despite the name, some of these require a screwdriver to actually dislodge, because they're pre-installed tightly; to that end, they're usually grooved on top.
Most PC cases have a headphone and microphone jack that terminates inside the case in a cable with a 10-pin header connector. This plugs into a pin grid on the motherboard, which, nowadays, is called an "HD Audio" header. In a nutshell, HD Audio brings auto-detection functionality to the ports, allowing the system to sense the presence of devices plugged into the ports so that it responds accordingly.
In earlier times, this connector on the board was known as an "AC '97" header, and during the transition time between the two, some motherboards provided a selector in the BIOS to let you switch the operation of the board's audio silicon between the AC '97 and HD Audio modes. (The pin connector is physically the same.) Older PC cases often have a forked audio-header cable with connectors for both HD Audio and AC '97. With a new motherboard and chassis, you'll definitely be using (and only seeing) the former connector--HD Audio is the current standard. Just be aware of these terms if you're recycling an older PC case; there, you may run across the venerable AC '97.
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