When Amazon launched the AWS EC2 cloud computing service back in 2006, per-hour billing was a real novelty.
The problem with per-hour billing, of course, was that it was necessary to pay for a full hour even in those instances when only a few minutes were used.
This provided an opportunity over the last several years for AWS's competitors, who slowly (but surely) moved to alternative billing models such as per-minute billing (which have proven to be far more flexible - and fair).
Starting Oct. 2, however, AWS once again upping its game and moving to per-second billing for its Linux-based EC2 instances. The new billing model will apply to on-demand, reserved and spot instances, as well as provisioned storage for EBS volumes.
Amazon EMR and AWS Batch are also reportedly moving to this per-second model (do note that there is a one-minute minimum charge per instance and that this development does not apply to those machines that run Windows or some of the Linux distributions that have their own separate hourly charges).