What computers are those in the picture?
These are Application Specific Integrated Circuit(s), a computer that is designed for Bitcoin mining. PCs used to mine too, but when FPGAs released (later ASICs released), mining with a PC wouldn't be efficient because of competing ASICs (and electricity fees).

Currently Bitmain (shop.bitmain.com) is the most preferred ASIC manufacturer, but it looks like it may not stay so, in a 6-12 months. (The most popular ASIC is Antminer S9, $1500, currently.)