I recently did some research into SFF PCs – small enough form-factor to be easily transported, and small enough form-factor to fit nicely into an entertainment unit or other media setup (though keep in mind that a SFF PC and a HTPC are not necessarily the same thing). Here are some notes from that research for everyone else interested in SFF PCs. Note you will see some disparity below between what gets a dash, a space, or a slash in its name. This is on purpose, and reflects the way these names seem to be commonly written and used, though clearly nothing is written in stone.
Form-factorsThere are several proprietary motherboard and PC form-factors out there, and often times the smallest examples are in fact unique designs. But, there are also some standard small form-factors, starting with the motherboard and working out to the rest of the PC. Here is a quick guide to some of the small form-factors out there, if you are not already familiar with them:
Mini-ATX: Was designed to use the same power supplies (and optionally cases) of a regular ATX motherboard, but conform to a smaller size. Mini-ATX is 11.2” x 8.2”, smaller in both dimensions than ATX. It is also easy to find, and very affordable, so while it is not the smallest form-factor by far, it is the most accessible if you are just looking to build a home system that uses a little less space than your average tower.
MicroATX: These boards were designed to use new, smaller power supplies (SFX), and conform to an even smaller size than Mini-ATX. They are used mostly in SFF desktop PCs, for example the very slim PCs you see from major retailers (though those are actually usually BTX boards, see below). They are harder to find and more expensive than Mini-ATX, but measure in at 9.6” x 9.6”.
FlexATX: These boards use the same power supply and mounting holes as MicroATX, but are even smaller. It does not seem to be a form-factor that ever caught on however, with very few examples of FlexATX boards available. The target size was 9” x 7.5”.
Micro-BTX: BTX was a board configuration launched to fix some of the problems with the layout of ATX boards, particularly when it comes to cooling. BTX boards are used heavily by major retailers (like Dell), but are rarer for the home-building crowd, partially because most people don’t see the need to move away from ATX. Micro-BTX, measuring 10.5” x 10.4”, was designed as a smaller board that uses the same power supply and mounting holes as a regular BTX board, making it the brother of the Mini-ATX board.
Pico-BTX: The proposed smaller form-factor in the BTX family, this design also seems to have never gotten off the ground. It measures 10.5” x 8”.
Mini-ITX: This is the form-factor that is probably the reason that FlexATX and Pico-BTX never got off the ground. Originated by Via Technologies, the board measures a slim 6.7” x 6.7” yet supports all the features of a full-sized motherboard. There are many Mini-ITX options out there, from Via and others, and a large home-building market that uses Mini-ITX boards in Home Theater PCs (HTPCs), car PCs, and elsewhere.
Nano-ITX: The successor to Mini-ITX, these boards are a mere 4.72” x 4.72”, making them almost as small as industrial embedded boards. So far there are fewer examples of these boards, but they are available from Via if not others.
Industrial BoardsThere are also a family of boards based around form-factors used in embedded computers – boards used in HVAC systems, assembly line robots, and vending machines. These boards are harder to get than the boards above, especially for the home enthusiast, and are more expensive. They often use special processors (like ARM and XScale), or rely on much older processors that don’t have the cooling needs of the newer P4 and later processors. However, if you are building a ruggedized, industrial PC, or a PC with special I/O needs, these are a good choice.
PC/104: A stackable form-factor that starts with the mainboard and then lets you stack similarly sized expansion modules on them. The modules attach via an ISA bus. The boards measure 3.8” x 3.6”.
PC/104-Plus: Measuring the same as above, this variant adds a 120-pin PCI bus option, and exists for compatibility between older modules and newer, PCI-based boards.
PCI-104: Again, the same size board, but in this specification it includes only the PCI bus.
EBX: Building up from the PC/104 specification, the EBX form-factor is a larger mainboard that still includes the expansion area so that you can stack normal PC/104-Plus expansion modules on it. The boards measure 8” x 5.75”.
EPIC: This form-factor was designed as a midway alternative between the small PC/104 and the EBX size. Like EBX, it still includes the option to stack modules on it. But it measures a smaller 6.5” x 4.53”.
Mini-ITXAs I said, if you are building a SFF PC yourself, Mini-ITX is a great option, as there are many resources readily available. Plus, you can order just one board, rather than a minimum quantity as is common with industrial boards (except when acquiring units for R+D).
Start out at Via themselves, who use their own processors on the board that have very low heat profiles. But, there are also options for Intel and AMD chip boards. Then, look at some of the many attractive case options, including HTPC cases. There are also automotive cases that use the case to dissipate all the heat and thus do not require a fragile fan, and options to use DC power supplies.