The Uptime Institute has created a Tier 1 to 4 classification system of data centers to demonstrate their ability to meet certain standards of operational reliability, also known as uptime. Tier 1, is the entry level classification of a data center. Each subsequent Tier adds additional redundancy requirements to the previous one, reaching Tier-4, the highest level of a fault tolerant data center. A Tier-1 data center requires space for IT systems, uninterruptible power supply, continuously working cooling equipment, and a power generator. A Tier-2 data center requires redundancy added to power and cooling systems, ensuring that some level of maintenance can take place without disrupting system operations. A Tier-3 data center has completely redundant power and cooling systems to ensure that all operations of the data center can be scheduled for maintenance without disrupting the IT operations.