Previous Generation Reserved Instances can be purchased directly from AWS for one year or three-year terms.

Using the Reserved Instance Marketplace, you have the flexibility to purchase Reserved Instances from AWS Reserved Instance Marketplace sellers for terms ranging between 1 month to 36 months (depending on available selection).

In either case, the one-time fee per instance is non-refundable. If your needs change, you can also request to move your Reserved Instance to another Availability Zone within the same region, change its Network Platform, or, for Linux/UNIX Reserved Instancess, modify the instance size of your reservation to another size in the same instance type at no additional cost.

Previous Generation Reserved Instances are billed for instance usage during the entire Reserved Instance term.

For Windows instances, Reserved Instance billing benefits only apply to one instance-hour per clock-hour. An instance-hour begins when an instance is started and continues for 60 minutes or until the instance is stopped or terminated—whichever happens first. A clock-hour is defined as the standard 24-hour clock that runs from midnight to midnight, and is divided into 24 hours (for example, 1:00:00 to 1:59:59 is one clock-hour).

For Linux instances, Reserved Instance billing benefits can apply to a maximum of 3600 seconds (one hour) of instance usage per clock-hour. You can run multiple instances concurrently, but can only receive the benefit of the Reserved Instance discount for a total of 3600 seconds per clock-hour; instance usage that exceeds 3600 seconds in a clock-hour is billed at the On-Demand rate. A clock-hour is defined as the standard 24-hour clock that runs from midnight to midnight, and is divided into 24 hours (for example, 1:00:00 to 1:59:59 is one clock-hour).

If Microsoft or Red Hat chooses to increase the license fees that it charges for Windows or Red Hat Enterprise Linux, we may correspondingly increase the per-hour usage rate for previously purchased Reserved Instances with Windows or Red Hat Enterprise Linux. The initial one-time payment for a Reserved Instance will be unaffected in this situation.

Any such changes for Windows would be made between Dec 1 – Jan 31, and with at least 30 days’ notice. Any such changes for Red Hat Enterprise Linux would be made at least 30 days’ notice.

If the per-hour usage rate does increase, you may continue to use your Reserved Instance with Windows or Red Hat Enterprise Linux with the new per-hour usage rate, convert your Reserved Instance with Windows or Red Hat Enterprise Linux to a Reserved Instance with Linux/UNIX, or request a pro rata refund of the upfront fee you paid for the Reserved Instance with Windows or Red Hat Enterprise Linux.

Previous Generation Reserved Instances are available for Linux/UNIX, Windows, Red Hat Enterprise Linux, and SUSE Linux Enterprise operating systems. You can also optionally reserve instances in Amazon VPC at the same prices as shown above.

From February 2nd 2015, Light and Medium Utilization Reserved Instances are no longer available for purchase from AWS. To view more information on these offerings, visit this page.