According to definitions from the Uptime Institute and TIA-942
(Telecommunications Infrastructure Standard for Data Centres), a
Tier 1 data centre is not required to have redundant power and
cooling infrastructures. It needs only a lock for security and can
tolerate up to 28.8 hours of downtime per year. In contrast, a Tier
4 data centre must have redundant systems for power and cooling,
with multiple distribution paths that are active and fault
tolerant. Furthermore, access should be controlled with biometric
readers and single-person entryways, gaseous fire suppression is
required, the cabling infrastructure should have a redundant
backbone, and the facility can permit no more than 0.4 hours of
downtime per year.