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# Tier definition¶

For more information about Drupal terms and terminology, see the Term index.

Tier has two different definitions, depending on whether you’re talking about server architecture or Acquia subscriptions.

## Server architecture¶

In server architecture, tier refers to whether you have multiple types of servers.

The following list describes the different tiers as it pertains to the Acquia Platform:

• Multi-tier: Multi-tier subscribers have Apache and MySQL running on separate servers.

For example, a multi-tier subscriber’s production environment can have a set of web servers (web-123 and web-124) running Apache, and a set of database servers (fsdb-123 and fsdb-124) running MySQL.

• Single-tier: Single-tier subscribers have Apache and MySQL running on the same server(s).

Note for Cloud Platform users

Cloud Platform Enterprise-level subscribers can be either single-tier or multi-tier; all Cloud Platform Professional subscribers are single-tier.

## Acquia subscriptions¶

Acquia subscribers have subscriptions that define their tier, which in turn defines the level of support they’re entitled to receive. For more information about subscription tiers, see: