General Purpose instances
provide customers with a balanced set of resources and a high level of processing performance on a low cost platform. Instances in this family are ideal for applications that require balanced CPU and memory performance. Examples of applications that will benefit from the performance of General Purpose instances include encoding, high traffic content management systems, and memcached.
Compute Optimized Instance.
Instances of this family have proportionally more CPU resources than memory (RAM) and are well suited for compute-intensive applications.
C4 instances are based on the Intel Xeon E5-2666 v3 ("Haswell") processor, and are designed to deliver the highest level of compute performance on Amazon EC2.
C3 instances are based on high frequency Intel Xeon E5-2680 v2 ("Ivy Bridge") processors, and are designed for running compute-intensive applications.
Instances of this family provide very high disk I/O performance or proportionally higher storage density per instance, and are ideally suited for applications that benefit from high sequential I/O performance across very large data sets. Storage-optimized instances also provide high levels of CPU, memory and network performance.
Micro instances (t1.micro)
provide a small amount of consistent CPU resources and allow you to increase CPU capacity in short bursts when additional cycles are available. They are well suited for lower throughput applications and web sites that require additional compute cycles periodically. You can learn more about how you can use Micro instances and appropriate applications in the Amazon EC2 documentation.
EC2 Compute Unit (ECU) – One EC2 Compute Unit (ECU) provides the equivalent CPU capacity of a 1.0-1.2 GHz 2007 Opteron or 2007 Xeon processor.