The majority of big web hosting companies have their own private data centers where all of their web servers are kept. Data Centers are specifically constructed to meet the environmental requirements of a web server. The data center's temperature, humidity, dust content, lighting, cleanliness, and security are painstakingly maintained by on-site employees who are in charge of maintaining all of the web servers in excellent working order. The floors are air-conditioned, all rooms have state-of-the-art fire extinguishing systems, and there is a 24-hour maintenance crew on duty seven days a week.