You can now launch M4 instances when using Amazon RDS for MySQL,MariaDB, PostgreSQL, and Oracle and SQL Server. M4 Instances fill a marvelous balance of compute,memory and network resources and are EBS-optimized by default. M4 instances comes in 5 sizes ranging from 2 to 40 vCPUs and 8 GB to 160 GB of memory, and fill superior performance and lower prices than RDS M3 instances. M4 instances feature a custom Intel Xeon E5-2676 v3 Haswell processor optimized specifically for AWS. They run at a base clock rate of 2.4 GHz and can recede as tall as 3.0 GHz with Intel Turbo Boost. To learn more about the benefits of the M4 instance families on Amazon RDS, or visit the DB Instance Classes page.
Source: amazon.com