<P> The primary advantage of an ATX motherboard as compared to an SBC is cost . Motherboards are manufactured by the millions for the consumer and office markets allowing tremendous economies of scale . Single - board computers are a market niche and are manufactured less often and at a higher cost . Motherboards and SBCs now offer similar levels of feature integration meaning that a motherboard failure in either standard will require equivalent replacement . </P> <P> One common variety of single board computer uses standardized computer form factors intended for use in a backplane enclosure . Some of these types are CompactPCI, PXI, VMEbus, VXI, and PICMG . SBCs have been built around various internal processing structures including the Intel architecture, multiprocessing architectures, and lower power processing systems like RISC and SPARC . In the Intel PC world, the intelligence and interface / control circuitry is placed on a plug - in board that is then inserted into a passive (or active) backplane . The end result is similar to having a system built with a motherboard, except that the backplane determines the slot configuration . Backplanes are available with a mix of slots (ISA, PCI, PCIX, PCI - Express, etc .), usually totaling 20 or fewer, meaning it will fit in a 19" rackmount enclosure (17" wide chassis). </P> <P> Some single - board computers have connectors which allow a stack of circuit boards, each containing expansion hardware, to be assembled without a traditional backplane . Examples of stacking SBC form factors include PC / 104, PC / 104 - Plus, PCI - 104, EPIC, and EBX; these systems are commonly available for use in embedded control systems . </P> <P> Stack - type SBCs often have memory provided on plug - cards such as SIMMs and DIMMs . Hard drive circuit boards are also not counted for determining if a computer is an SBC or not for two reasons, firstly because the HDD is regarded as a single block storage unit, and secondly because the SBC may not require a hard drive at all as most can be booted from their network connections . </P>

Which of the following server types is in the form of a single circuit board