Microsoft Publishes Some Details on the New Azure B-Series VMs

Last week I blogged about how the pricing of a new B-Series (burstable CPU) virtual machine appeared online. At the time, we knew almost nothing about the machines other than their intended workloads: anything with normally low CPU utilization that could temporarily burst, such as test/dev or low-end web/application servers.

While updating an article for, I found that the official specs of Azure VMs had been updated to include the B-Series:

The B-Series provides these customers the ability to purchase a VM size with a price conscience baseline performance that allows the VM instance to build up credits when the VM is utilizing less than its base performance. When the VM has accumulated credit, the VM can burst above the VM’s baseline using up to 100% of the CPU when your application requires the higher CPU performance.

That means that this is very similar to the AWS T2 Instances. By default, your machine’s CPU is artificially capped. By underutilizing the CPU, the machine can earn & bank credits that can be later used. This bank has a hard limit, depending on the size of the machine. Should the service in the machine need more CPU, those credits can be burned to go beyond the artificial cap to use the underlying physical cores potential. In other words, the less you use the CPU, the more horsepower you get for those times when you need it.

Here are some details on the sizes in the B-Series.

  • All of the machines are S-variants
  • Each machine has a small amount of SSD temporary storage.
  • Note how the disk stats refer to “max local disk”. Hmm!


Right now, there is a limited access preview for the B-Series in just a few regions:

  • West Europe
  • West US 2
  • East US
  • Asia Pacific – Southeast

I can see the B-Series in my subscriptions, but I cannot deploy it – the quota is set to 0 and the blade for requesting an increase does not include the B-Series. I guess this is still a private preview for now, and things might change on Sept 25th (Ignite).

Azure Low Cost “Burstable” CPU Virtual Machines

Microsoft has released pricing for a new kind of virtual machine in Azure, called the B-Series. The key traits of this VM type are:

  • It is 1/4 the price of a similar A_v2-Series machine.
  • The CPU runs at a low rate, and “bursts” on demand for higher capacity jobs.

I’d love to have more information to share, but all we have is all I stumbled upon in the pricing pages last week:


As you can see in the names, they comply with the “new” format. That S in the names suggests that these machines support Premium (SSD) storage disks.

These are low end machines, as you can see by the entry level 1 core & 1 GB RAM model. The Microsoft VM pricing page says that they are good for:

… development and test servers, low traffic web servers, small databases, micro services, servers for proof-of-concepts, build servers, and code repositories.

The costs are really low. The B2S is just €20.71 per month, compared with €85.33 for the A2_v2 – both having 2 cores and 4 GB RAM. If you want a low end web server, then that’s a seriously cheap offering!

AWS does have something called T2 Instances. These are VMs that offer CPU burst-ability based on credits earned for low CPU utilization. The rough language of suitable roles is similar to that of the Azure B-Series. However, we have no detailed information on the B-Series yet – my bet is that will be published on September 25th (Ignite day 1).