Instance Families and Types

When you launch an instance, you specify the instance type (the value in the Name column in the following table). We launch an m1.small if you don't specify a particular instance type.

	Note
	The cg1.x4large instance type has 23 GB of memory, with 1 GB reserved for GPU operation. The 22 GB doesn't include the on-board memory of the GPUs, which is 3 GB per GPU for the NVIDIA Tesla M2050.

Amazon EC2 instances can run Microsoft Windows Server 2003, Microsoft Windows Server 2008 or Microsoft Windows Server 2008 R2. The Windows AMIs provide you with all standard Microsoft Windows Server functionality.

Using Amazon EC2 instances running Windows is similar to using instances running Linux/UNIX. The following are the major differences between instances that use Linux/UNIX and Windows:

Amazon EC2 currently provides the following Windows AMIs:

The Windows public AMIs that Amazon provides are unmodified versions of Windows with the following two exceptions: we added drivers to improve the networking and disk I/O performance and we created the Amazon EC2 configuration service. The Amazon EC2 configuration service performs the following functions:

For more information about the EC2 configuration service, see Appendix C: Windows Configuration Service.

Transitioning to a utility computing model changes how developers are trained to think about CPU resources. Instead of purchasing or leasing a particular processor to use for several months or years, you are renting capacity by the hour. Because Amazon EC2 is built on commodity hardware, over time there might be several different types of physical processors underlying different virtual EC2 instances. Our goal is to provide a consistent amount of CPU capacity regardless of the actual underlying hardware.

Amazon EC2 uses a variety of measures to provide each instance with a consistent and predictable amount of CPU capacity. To make it easy for developers to compare CPU capacity between different instance types, we defined an Amazon EC2 Compute Unit. One EC2 Compute Unit provides the equivalent CPU capacity of a 1.0-1.2 GHz 2007 Opteron or 2007 Xeon processor. This is also the equivalent to an early-2006 1.7 GHz Xeon processor referenced in our original documentation.

	Note
	We use several internal benchmarks and tests to manage the consistency and predictability of the performance of an Amazon EC2 Compute Unit. For more information, go to the Instance page.

To find out which instance works best for your application, we recommend launching an instance and using your own benchmark application. This helps you determine which instance type works best for your specific use case.

Amazon EC2 provides virtualized server instances. Whereas some resources like CPU, memory, and instance storage are dedicated to a particular instance, other resources such as the network and the disk subsystem are shared among instances. If each instance on a physical host tries to use as much of one of these shared resources as possible, each receives an equal share of that resource. However, when a resource is under-utilized, you are often able to consume a higher share of that resource while it is available.

The different instance types provide higher or lower minimum performance from the shared resources depending on their size. Each of the instance types has an I/O performance indicator (low, moderate, high, etc.). Instance types with high I/O performance have a larger allocation of shared resources. Allocating larger share of shared resources also reduces the variance of I/O performance. For most applications, moderate I/O performance is more than enough. However, for applications that require greater or more consistent I/O performance, consider instances with higher I/O performance.

To help categorize and manage your instances, you can assign tags of your choice to them. For more information, see Using Tags .