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Small form factor (SFF) is a classification ofdesktop computers and for some of their components,chassis andmotherboard, to indicate that they are designed in accordance with one of several standardizedform factors intended to minimize thevolume and footprint of adesktop computer compared to the standardATX form factor.
For comparison purposes, the size of an SFF case is usually measured inlitres. SFFs are available in a variety of sizes and shapes, including shoeboxes, cubes, and book-sized PCs. Their smaller and often lighter construction has made them popular ashome theater PCs and asgaming computers for attendingLAN parties. Manufacturers also emphasize theaesthetic andergonomic design of SFFs since users are more likely to place them on top of a desk or carry them around. Advancements in technology combined with a reduced size enables a powerful computer to be a smaller size.[1]
Small form factor designs do not include computing devices that have traditionally been small, such asembedded ormobile systems.[2] However, "small form factor" lacks anormative definition and is consequently open to interpretation and misuse. Manufacturers often provide definitions that serve the interests of their products.[3] According to marketing strategy, one manufacturer may decide to mark their product as "small form factor" while other manufacturers are using different marketing name (such as "Minitower", "Microtower" or "Desktop") for personal computers of similar or even smaller footprint.
The acronym SFF originally stood for "Shuttle Form Factor," describing shoebox-sized personal computers with two expansion slots.[4] The meaning of SFF evolved to include other, similar PC designs from brands such as AOpen and First International Computer, with the word "Small" replacing the word "Shuttle".
The term SFF is used in contrast with terms for larger systems such as "mini-towers" and "desktops."[5]
Small form factor computers are generally designed to support the same features as moderndesktop computers, but in a smaller space. Most accept standardx86microprocessors, standardDIMM memory modules, standard 8.9 cm (3.5")hard disks, and standard 13.3 cm (5.25")optical drives.
However, the small size of SFF cases may limit expansion options; many commercial offerings provide only one 8.9 cm (3.5")drive bay and one or two 13.3 cm (5.25") external bays. StandardCPUheatsinks do not always fit inside an SFF computer, so some manufacturers provide customcooling systems. Though limited to one or twoexpansion cards, a few have the space for3⁄4-length cards such as the GeForce GTX-295.[6] Most SFF computers use highlyintegrated motherboards containing many on-board peripherals, reducing the need for expansion cards. As of 2020 many SFF PC cases do not include any expansion bays larger than 2.5 inches[7] (large enough to accommodate SATA SSDs), due to the declining popularity of optical disc drives[8][9][10][11] and 3.5-inch hard drives in the consumer space.[12]
Even if labeled "SFF," cube-style cases that support full-sized (PS2 form factor) power supplies actually have a microATX form factor. True SFF systems useSFX,TFX or smaller power supplies[citation needed], and some require a laptop-style external "power brick."
Some SFF computers even include compact components designed formobile computers, such as notebookoptical drives, notebook memory modules, notebook processors, and externalAC adapters, rather than the internalpower supply units found in full-size desktop computers.
Crowdfunding and availability of rapid prototyping tools has enabled the production of several mini-ITX cases focusing on efficiently organizing commercial computer components into small volumes including theNcase M1,[13] Ghost S1,[14][15] DAN A4-SFX,[16][17] and Thor Zone MJOLNIR.[18][19] Communities of enthusiasts[20][21] and reviewers[22] now develop and promote enhanced SFF assembly, maintenance, and performance criteria.3D printing andlaser cutting have enabled customization and one-off production by both manufacturers like Lazer3D[23] and individual users[24] with access to the relevant equipment.
The many different types of SFFs[25] are categorized loosely by their shape and size. The types below are available as of 2013[update].
Many SFF computers have a cubic shape. Smaller models are typically sold asbarebones units, including a case,motherboard, and power supply designed to fit together. The motherboard lies 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. ThePower Mac G4 Cube, released in 2000, and the Shuttle XPC are good examples of this design.MSI andAsus produce similar designs. TheXi3 Modular Computer is an example of a cube computer with a little more upgrade possibilities.
Shuttle has adapted several of its XPC models (some 5-series and most later) to alternately acceptmini-ITX motherboards. The base of the XPC is provided with mounting points which accommodate both "Shuttle form factor" (ShFF) and mini-ITX motherboards. In order to accommodate mini-ITX motherboards, two of the ShFF mounting points are simply relocated (the remaining mini-ITX mounting points are in common with the remaining ShFF mounting points). A "standard" ShFF motherboard is 20.6 cm (8 1/8″) wide by 27.3 cm (10 3/4″) deep, with the I/O shield and the two PCI slots being located in common with mini-ITX motherboards. Most ShFF systems utilize Shuttle's proprietary heat pipe (liquid cooling) system, "Integrated Cooling Engine" (ICE), for the processor, although several also feature heat pipe cooling for the voltage regulator and/or the chip set (Northbridge). When an ShFF system is upgraded to a mini-ITX motherboard, an Intel or compatible processor fan must replace the ICE cooler. The ShFF's ICEcomputer fan is so designed that it may be repurposed as a case fan when the case is upgraded to mini-ITX use. When so upgraded, the repurposed fan would be connected to the motherboard's case fan connector (3-pin) while the new CPU fan would be connected to the motherboard's CPU fan connector (4-pin).
AOpen Inc. produced a stackable S120[26] case, allowing the user to stack up to four components vertically or horizontally. These layers can be for add-on cards, optical drives, and hard drives, using either internal power supplies or external AC adapter power sources. After the S120, AOpen made more small form factor cases for systems with Micro ATX and Mini-ITX.
The graphics card is placed behind the motherboard andPSU, connecting to it via aPCI Express x16 extension cable. This design is popular with SFF enthusiasts as it packs high-performance hardware into a small space while providing adequate cooling. Water cooling radiators may be added on to the top, bottom or sides to further increase cooling capacity. An electrically insulating sheet, such asthermoplastic polyurethane, may be placed between the motherboard/PSU and graphics card to implement separate airflow zones, isolating heat sources from each other to improve cooling.[27][28]
Resembling a gaming console (such asXbox One orPlayStation 4), the graphics card is placed directly above or below the motherboard and PSU. The graphics card is connected to motherboard with a PCIe x16 extension cable. This form factor is popular for those with a lack of desk or floor space as the footprint is small when placed vertically. It may also fit nicely into a TV cabinet/shelf and act as a cheaper, faster, upgradable alternative to gaming consoles. The graphics card may be sectioned off internally as to isolate it from the heat produced by the CPU.[29][30]
Until 2005, SFF cases were usually sold as barebones units (case, power supply, and motherboard) to system integrators and home-based builders. In 2005,Apple Inc. introduced itsMac Mini (volume of 1.4L, excluding externalpower brick). Later in the same year, the first AOpen mini PC MP915 (renamed to XC mini in 2007 since "mini PC" could not be registered as a trademark), was announced. The size of the XC mini series PC—16.5(W) × 5.0(H) × 16.5(D) cm—makes it one of the smallest desktop PC systems (1.3L volume). It was criticized for looking like the Apple Mac Mini but Apple has not taken action on this subject. In February 2007, AOpen redesigned the case of the mini PC MP945 series.
Since 2006, majorOEM PC brands such asHP andDell have begun to sell fully assembled SFF systems. These are often described asbookshelf units since they resemble a miniature tower case small enough to fit on a bookshelf. The HP Slimline series andDell Dimension C521 (volume 1.65 L) are good examples of this trend. The Maxdata Favorite 300XS is another mini computer. The HP Slimline uses a non-standard motherboard that is very similar in size to Mini-ITX.[31]
In addition to its industrial use, the extremely smallMini-ITX motherboard form factor has also been incorporated into SFF computers. These are often extremely compact, incorporating low-power components such as theVIA C3 processors. The Travla C134 is an example of this design. At 17.8 x 25.4 x 5.1 cm (7 × 10 × 2") the Travla C134 is somewhat larger than the Mac mini which is 16.5 x 16.5 x 5.1 cm (6.5 × 6.5 × 2") and barely bigger than a standard 13.3 cm (5.25")optical drive.
Beginning in 2007, several other companies have released other very small computers that besides a small size, focus on a low price, and extremely high power efficiency (typically 10 W or below in use). These include theZonbu,fit-PC,Linutop, andA9home. With the release ofIntel Atom CPU, AOpen also made Nettop systems: the uBox series with model LE200 and LE210.[32] The uBox series equips a dual-core Intel Atom 270/330 processor, single-channel DDR-II 533/667 memory, Intel 945GC+ICH7 chipset, three SATA connectors and 5.1-channel high-definition audio output.
Apple's2024 Mac mini with theM4system-on-a-chip (SoC) features a significantly smaller design than earlier models, with a 5x5-inch form factor often described as slightly larger than anApple TV 4K.[33]
Essentially a bookshelf-style case lying on its side, a miniatureHTPC replicates the look of other smaller-than-rack-sized home theatre components such as aDVR or miniaudio receiver. The front panel interface is emphasized, with the optical disc drive rotated relative to the case in order to maintain horizontal mounting, and more motherboard port connectors (such as forUSB) are routed to the front panel, they normally are as powerful as PC desktops.
Acomputer-on-module (COM) is a completecomputer built on a singlecircuit board. They are often used asembedded systems due to their small physical size and low power consumption.
Each model of Dell'sOptiPlex line of computers typically includes anUltra-Small Form Factor (USFF) chassis option. In theCore 2 era, these machines used 8.9 cm (3.5") desktop hard drives and external power supplies, such as the OptiPlex 745 and 755. More recent units use 6.4 cm (2.5") laptop hard drives and have integrated power supplies, such as the OptiPlex 990 USFF. The compact size comes at the cost of restricted expandability, as USFF models have no PCI or PCIe slots and may have limited CPU and memory options.
Starting from Series 5, USFF was replaced with Micro variants, an even smaller size option that usesexternal power supplies and does not have optical drives.
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Understood as comprisingnano-ITX (12 × 12 cm) andpico-ITX (10 × 7.2 cm) boards, the format was championed byVIA Technologies.[34] Intel now describes its ownNext Unit of Computing (NUC) products (10.2 x 10.2 cm or 4 × 4") as UCFF.[35]
Yes, early small-form-factor machines (let's just call 'em SFFs) had some issues. OK, alot of issues. Designed for the gimpiest casual user, these mini-PCs didn't offer many options in the way of upgrades or power. The cases were often too small to fit a full-size videocard [...] Still, two very specific users saw the SFFs' potential. First, home theater enthusiasts realized that these pint-sized PCs made for ideal media center hubs, and second, LAN partygoers naturally glommed on to them for the portability factor. [...] we could see the SFF market gaining a lot more momentum. Until then, enjoy being the first on your block to squeeze a full-size tower's worth of top-level gear into a shoebox-size package.
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