One of the the things to consider when deciding if Windows Azure is right for your solution is pricing. Windows Azure’s pricing is based on four factors: Computing, Storage, Storage Transactions, and Bandwidth. The computing factor is priced on a per hour basis. This concept has raised the question “What is a compute hour?”
A compute hour is basically the duration at which a role instance runs. A role instance represents either a Web Role or a Worker Role (an overview of each is provided here). Once deployed, each of these roles can have one or more instances running. This approach gives you the flexibility to quickly scale your application to use multiple instances if necessary.
As an example, imagine having a worker role that is responsible for processing electronically submitted orders. If this worker role was deployed for use in a smaller business, a single instance may be appropriate. If you were to keep this instance running for a single day, your compute cost would be calculated as:
1 (instance) x 24 (hours in a day) x .12 (cents per computer hour at the time of writing) = $2.88
Now imagine that the orders start flowing in faster than your single instance can adequately handle. In less than 5 minutes you can have a second instance up and running. Significantly, your cost only increases marginally as shown here:
2 (instances) x 24 (hours in a day) x .12 (cents per computer hour at the time of writing) = $5.76
You are only billed for role instances that are running. Because it is so easy to start and stop instances, you may choose to only use a role instance when you really need it. As an example, you may decide it appropriate to only run a role instance once a day, or once a week, or maybe just once a month. As you can imagine, the savings compared to purchasing a traditional server, or even using a virtual server, is quite significant.
I hope this helps explain what a compute hour is. If not, please let me know in the comments. If you would like to learn how to develop software on Windows Azure, I personally recommend the book Azure in Action. My review of this great book can be found here.
i would prefer that compute hours are calculated only when the unit is actually being used. if there's 0 activity (measured by CPU utilization?) on the instance in 8 out of 24 hrs, i'd prefer not to pay for those 8 hours. That would be the pinnacle of flexibility and cost savings!
i would prefer that compute hours are calculated only when the unit is actually being used. if there’s 0 activity (measured by CPU utilization?) on the instance in 8 out of 24 hrs, i’d prefer not to pay for those 8 hours. That would be the pinnacle of flexibility and cost savings!