Barebones P/N: ZBOX-BI320-U
Mini PC P/N: ZBOX-BI320-U-W2
(The "U" means USA market, the "W2" includes Windows)
In my opinion, the mini PC is the one to get, even if you don't want Windows 8.1 w/Bing. It alone includes the mSATA mini PCIe slot on the back of the motherboard. The barebones model has the solder pads, but not the connector.
This is an inexpensive complete desktop PC. It's price jumps around between $160-$200. I purchased it on sale from Newegg for $140. Amazon sells it as well. You can track its price over time on camelcamelcamel.com (ASIN B00M2UKY1Q). The "usual" sale price is $159.
- CPU: Haswell Celeron 2957U (1.40GHz)
RAM: two slots, one comes populated with a 2GB DDR3 1.35V SODIMM
HDD: comes with a 64GB mSATA SSD (preinstalled underside of motherboard), PLUS a 2.5" tool-less HDD site.
OS: Windows 8.1 with Bing, 64-bit;includes reinstallation media
Even with 2GB of RAM, the system was perfectly responsive in everyday basic use. I honestly do not notice a performance difference with the second stick of RAM, but I haven't tried opening 50 firefox tabs or anything yet.
The case is very cheap, thin plastic. It's easy to open (two thumb screws), exposing the RAM slots and 2.5” HDD site.
The 64GB SSD is made by Forsee, model# S600M064G. It's actually not that bad! In my brief experience so far, the biggest limitation is the CPU. I've kept task manager open, casually keeping an eye on CPU usage. Even seemingly simple tasks peg one or both CPU cores. Windows updates and Disc Cleanup, for example.
It's about 25cm closer to me than my gaming PC, and it's quieter. Even with the CPU at 99% (Windows Updates?!) the fan speed did not increase and the outlet air wasn't noticeably warm. It's not silent, but it's very quiet. It's a soft “hiss” more or less.
Power consumption measurements with my kill-a-watt:
Off = 1W
Boot peak = 13W
Win 8.1 desktop idle = 5W
1080p full-screen youtube = 10W
Windows Disc Cleanup (99% CPU) = 11-12W!
I'm watching for a deal/steal on a 2.5" HDD to see how this performs as a little file server. At ~5 watts idle, that beats my current lowest-power file server by 10 watts! I picture an identical pair of these little machines with 1TB HDDs, a primary NAS and a mirror that wakes up to do nightly backups.