Small Form Factor PC
For comparison purposes, the size of an SFF case is usually measured in litres. 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 as home theater PCs and as gaming computers for attending LAN parties. Manufacturers also emphasize the aesthetic and ergonomic 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.
Small form factor designs do not include computing devices that have traditionally been small, such as embedded or mobile systems. However, "small form factor" lacks a normative definition and is consequently open to interpretation and misuse. Manufacturers often provide definitions that serve the interests of their products. 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.
History
The acronym SFF originally stood for "Shuttle Form Factor," describing shoebox-sized personal computers with two expansion slots. 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."
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 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. Standard CPU heatsinks do not always fit inside an SFF computer, so some manufacturers provide custom cooling systems. Though limited to one or two expansion cards, a few have the space for 3⁄4-length cards such as the GeForce GTX-295. Most SFF computers use highly integrated 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 (large enough to accommodate SATA SSDs), due to the declining popularity of optical disc drives and 3.5-inch hard drives in the consumer space.
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 use SFX, TFX or smaller power supplies , and some require a laptop-style external "power brick."
Some SFF computers even include compact components designed for mobile 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.
Enthusiast community and crowdfunding
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 the Ghost S1, DAN A4-SFX, and Thor Zone MJOLNIR. Communities of enthusiasts and reviewers now develop and promote enhanced SFF assembly, maintenance, and performance criteria. 3D printing and laser cutting have enabled customization and one-off production by both manufacturers like Lazer3D and individual users with access to the relevant equipment.
SFF types
The many different types of SFFs are categorized loosely by their shape and size. The types below are available as of 2013.
Cubic / Shoebox
Many SFF computers have a cubic shape. Smaller models are typically sold as barebones 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. The Power Mac G4 Cube, released in 2000, and the Shuttle XPC are good examples of this design. MSI and Asus produce similar designs. The Xi3 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 accept mini-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 ICE computer 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 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.