Maybe we can call blade server a box which consist of rack server. For example intel modular server is a blade server it has got 6 modules which consist of 2 cpu and 12 dim slot. Blade systems very effective, cheap and easy to manage. So all over the word lots of hosting company using blade servers . Because of blade systems advantages
Firstly, easy to manage.
Blade system can manage one console and they have switch and storage unit so 1 operator can manage two or three blade maybe 25 and 40 server
Secondly, the blade systems is cheaper than rack systems
For example, if you need to buy 6 rack server you have to pay 6 power suply, 12 or 16 fan and 6 raid controler price . But if you buy blade systems only pay box price 2 power unit and 2 reduant fan unit that is all. Another price is same cpu , disk etc.
When compared to other traditional rack-mount servers, a blade server can be dedicated to a single task, such as:
Database and application hosts
Virtual server host platforms
Remote desktop or workstations
Web page serving and caching
SSL encrypting of Web communication
Transcoding of Web page content for smaller displays
Streaming audio and video content