The Shuttle DS57U is powered by a dual core Celeron 3205U running at 1.5GHz and a nice and cool 15W TDP.  The system supports up to 16GB of DDR3 at 1.35 V, no 1.5V DIMM that TechPowerUp tried would work and for add-in cards you have a single full sized mini-PCIE slot and a half sized mini-PCIE slot which is already occupied by a WLAN card.  The system does have only one SATA 6Gbps port so external storage may be necessary, thankfully there are a pair of USB 3.0 ports and four USB 2.0 ports.  This model is available for $250 currently, if you decide you need more power there are several versions going all the way up to the DS57U7 powered by an i7-5500U.  If you are looking for an inexpensive SFF barebones system, Shuttle is not a bad choice overall and the DS57U is worthy of consideration.

"The Shuttle DS57U is a slim barebone PC that only needs RAM and a HDD or, even better, an SSD to boot. It comes with an Intel dual-core Celeron processor (Broadwell) and features lots of I/O ports, which make it suitable for a wide range of applications."

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