The machine images are like templates that are configured with an operating system and other software, which determine the user’s operating environment. AMI types are categorized according to region, operating system, system architecture (32- or 64-bit), launch permissions and whether they are backed by Amazon EBS or backed by the instance store.
Each AMI includes a template for the root volume required for a particular type of instance; a typical example might contain an operating system, an application server and applications. Permissions are controlled to constrain AMIs for instance launches to the appropriate AWS accounts. A block device mapping ensures that the correct volumes are attached to the launched instance.
Users can select an AMI provided by AWS, the user community, or through the AWS Marketplace. Users can also create their own AMIs and share them.