Small form factor (desktop and motherboard)

Small form factor (SFF) computers are housed in smaller cases than typical desktop computers. While the term has no exact definition, it generally includes cases designed for motherboards smaller than the standard ATX form factor. It generally excludes rack-mount cases, blade servers, and industrial computers, which are designed for data center and factory use, rather than home and office environments.

The size of SFF PCs vary widely, from 1 L to 30 L or more, but as of 2007 the volume of a shoe box is typical. Their shapes vary from cubes to mini-towers to shallow flat cases resembling home theater components (such as VCRs or AV receivers).

Uses

Because they are built around small motherboards, SFF computers can be far smaller than typical desktop computers. They are often used in space-limited areas where normal computers cannot be placed. SFF computers have also found a niche as home theater PCs, as well as for mobile applications such as LAN parties. Many users simply enjoy the esthetic and ergonomic benefits of a small system which, unlike a full-size tower case, can easily fit on top of a small desk.

Some SFF computers go further, employing more compact components designed for portable computers, such as notebook optical drives, notebook memory modules, notebook processors, and external AC adapters rather than the internal power supply units found in full-size desktop computers.

Features

Small form factor computers are generally designed to support the same features as modern desktop computers, but in a smaller space. Most accept standard x86 microprocessors, standard DIMM memory modules, standard 3.5 inch hard disks, and notebook 5.25 inch optical drives.

However, the small size of SFF cases may limit expansion options; many commercial offerings provide only one 3.5" drive bay and one or two 5.25" external bays. Standard CPU heatsinks don't always fit inside an SFF computer, so some manufacturers provide custom cooling systems. Many SFF cases only have room for one to four expansion cards, although very few have the space for larger cards— such as the GeForce 8800GTX—. Many SFF computers use highly integrated motherboards containing many on-board peripherals so that expansion cards are not needed; many of these motherboards use custom form factors, while others use the microATX standard.

Some "box type" SFF cases (recently very popular) can fit standard ATX power supplies, while others require custom power supplies or external power bricks.

SFF Types

There are many different types of SFF computers^[1] available as of 2008. They may be categorized loosely by their overall shape and size.

Cubical

Many SFF computers have a cubical or nearly cubical shape. Smaller models are typically sold as barebones units, including a case, motherboard, and power supply designed to fit together. The motherboard lays flat against the base of the case. Upgrade options may be limited by the non-standard motherboards, cramped interior space, and power and airflow concerns. The Apple Macintosh [1] released in 2000, and the Shuttle XPC are good examples of this design. MSI and ASUS produce similar designs.

Larger cases, called box type, tend to have a shoe box structure to them. They take microATX motherboards which, again, lay flat on the base of the case. They are normally sold as bare cases which can be easily upgraded thanks to the standard motherboard form factor and greater internal space. The Antec NSK1300, APEVIA X-QPack, PC Design Lab's Qmicra, Silverstone SG01 (SG01 Review) and Ultra Micro Fly are common examples of box type SFF computers.

Flat or Pizza Box

These are low, flat cases resembling the pizza box form factor which was formerly very popular for computer workstations. They usually fit microATX motherboards which lay flat on the base or side of the case (depending on how it is oriented in use). The NeXT NeXTStation from the early 1990s is a good example of this case design.

Many cases designed for home theater purposes are based on this design (though others are too large to be considered SFF). They feature front-panel controls, ports, and styling designed to reproduce the look and convenience of traditional home theater components such as VCRs and DVD players. The NMEDIAPC HTPC 180 is an example of this design.

Lunch Box

A Lunchbox case is a narrow, high-profile enclosure designed to sit horizontally and support a monitor. They usually have fewer expansion slots than full desktop cases but are otherwise similar. Some past computers in lunch box cases include the Apple Macintosh IIci, the SPARCstation ZX and ACME, EMP370. Roughly equivalent to a minitower on its side, this design is seldom used for new hardware, for similar reasons as Pizza boxes.

Bookshelf computers

Until recently, SFF cases were usually sold alone, or as barebones units (case, power supply, and motherboard). They were marketed primarily to enthusiasts who wanted to build their own custom computers. In 2005, Apple Inc. introduced its Mac Mini (volume of 1.4 L, excluding external power brick). As of 2006, major OEM PC brands such as HP and Dell have begun to sell fully-assembled SFF systems. These are often described as bookshelf units since they resemble a miniature tower case small enough to fit on a bookshelf.

The HP Slimline series and Dell C521 (volume 1.65 L) are good examples of this trend. As of 2007, several other companies have released similar computers that focus on small size, low price, and extremely high power efficiency (typically 10 W or below in use). Zonbu, fit-PC, Linutop, and a9home are examples of these.

The HP Slimline uses a non-standard motherboard that is very similar in size to Mini-ITX.^[2]

Mini-ITX

In addition to its industrial use, the extremely small Mini-ITX motherboard form factor has also been incorporated into SFF computers. These are often extremely compact and incorporate low-power components such as the VIA C3 processors. The Travla C134 is an example of this design; it is somewhat larger than the Mac mini (7x10x2" vs 6.5x6.5x2"), and barely bigger than a notebook 5.25" optical drive.

microATX tower

microATX towers resemble normal tower cases but are shorter in height, and sometimes depth. They are designed to fit microATX motherboards, but not larger ATX motherboards. They may use standard ATX power supplies, or may come with proprietary PSUs. The Antec NSK3300 (volume of nearly 25 L) and Silverstone SG03 (volume around 22 L) are examples of microATX tower cases.

Because they are very similar to full-size tower cases, microATX tower cases are not always recognized as small form factor cases.

DTX Standard

On January 10, 2007, AMD announced a new standard form factor for SFF motherboards, called DTX. The dimensions of DTX motherboards will be 203mm×244mm, while microATX are 244mm×244mm. A shortened version, Mini-DTX, will measure 170mm×203mm

In designing DTX, AMD sought to address the following issues:

Manufacturing cost:
- DTX will allow up to four motherboards to be produced from a standard printed circuit board panel (Mini-DTX will allow up to six motherboards per standard panel)
- DTX motherboards can be manufactured with as few as four layers of PCB wiring.
Backwards-compatibility. DTX motherboards are smaller than microATX boards, but backwards-compatible with them. In other words, DTX motherboards will fit inside cases designed for microATX boards. This will reduce the hurdle of transitioning from microATX to DTX for SFF computer builders.
Standardization. If DTX becomes an established standard, SFF builders (both commercial builders and hobbyists) will have a wider range of interchangeable cases, motherboards, and power supplies to choose from.

References

^ "List of Small Form Factors," PC/104 and Small Form Factors, 2008
^ HP and Compaq Desktop PCs - Motherboard Specifications, PTGV-DM (Onyx2)

External links

[1] "List of Small Form Factors," PC/104 and Small Form Factors, 2008

[2] HP and Compaq Desktop PCs - Motherboard Specifications, PTGV-DM (Onyx2)

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