The term Azure series identifies the available performance levels of an IaaS deployment (provision of a cloud service and/or a VM). The performance levels (that is, the instance) generally differ in the number of CPU cores, the amount of memory, and the maximum size of the data disk.

Some performance levels or even entire Azure series are also defined by special hardware equipment.

Microsoft currently offers the following Azure series:

• A-series: The A-series supports the full feature scope of Azure VMs for a wide range of workloads.
• Basic A: Light version of the A-series (only available for instances A0-A4). Designed for development and testing starter workloads.
• A-series (compute intensive): High-end version of the A-series. Designed for high-performance computing and data-intensive workloads (for example, video encoding). Optional with high-throughput network interfaces (RDMA).
• A-series version 2 (Av2-series): Av2-series is the latest generation of the A-series and it is specifically designed for Azure DevTest Lab scenarios or for use as an Azure Service Fabric (a microservice architecture). With Av2-series, the performance in data access is significantly higher, since only Solid State Drives (SSD) are used for data storage.
• B-Series: Series BS is intended for workloads that do not require the full CPU performance continuous, such as web servers, or development and test environments. Each instance of the Series BS provides a basic level (minimum value) for the performance and has then the possibility to extend to a 100% CPU utilization of an Intel® Broadwell E5-2673 v4 2.3GHz or an Intel® Haswell 2.4 GHz E5-2673 v3 processor. As long as you use less than the basic performance with the VM instance, you acquire a credit balance. As soon as your credit has been formed, you can also use the performance that goes beyond the basic level.

All you have to do is answer the question: which basic level best suits my needs? Each instance of the BS Series supports Azure premium storage by default.

• D-series and DS-series: D-series VMs are designed to run applications that demand higher compute power and temporary disk performance. To achieve this, a D-series VM provides a better processors performance, a higher memory-to-core ratio, and a SSD are used for the temporary disk.
• D-series and DS-series version 2 (Dv2-series and DSv2-series): Dv2-series and DSv2-series are the next generation of the D-series and DS-series. Dv2-series and DSv2-series are identical to the original series, but have a 35% higher CPU performance based on the Intel Xeon® E5-2673 v3 (Haswell) processor.
• D-series and DS-series version 3 (Dv3-series and Dsv3-series): Dv3-series and Dsv3-series are the latest generation of the D-series and DS-series. Dv3-series and Dsv3-series are based on the Intel® Broadwell E5-2673 v4 2.3 GHz processor, or the Intel® Haswell 2.4 GHz E5-2673 v3 processor and introduce Hyper-Threading Technology and virtual CPUs (vCPUs) as key architecture elements. The new series provides also some of the first VM's to be running on a Windows Server 2016 host. Windows 2016 hosts enable nested virtualization and Hyper-V containers for these new instances. Nested virtualization allows you to run a Hyper-V server on an Azure Virtual Machine.
• Ev3 and ES-series version 3 (Ev3-series and Esv3-series): Ev3-series and Esv3-series are also a part from the latest generation of the D-series and DS-series and the new name for the high memory instances D11 - D14. For the Ev3-series and Esv3-series, the same description applies as for the Dv3-series and Dsv3-series.
• F-series and FS-series: F-series and FS-series offers a high CPU-to-RAM ratio, ideal for web servers, network appliances, batch processing, and medium-load application servers or real-time communication.
• FS-series version 2 (Fsv2): Fsv2-series are the next generation of the FS-series. The Fsv2-series offers are based on the fastest Intel® Xeon® Scalable processor, code-named Skylake (Intel® Xeon® Platinum 8168 processor), and featuring a base core frequency of 2.7 GHz and a maximum single-core turbo frequency of 3.7 GHz. Fsv2-series provides the Hyper-Threading Technology and the Intel® AVX 512 instructions set, as key architecture elements.
• G-series and GS-series: G-series and GS-series are a clone of the older D-series and DS-series, but the G instances have a twice larger memory and four times larger temporary disks based on an SSD. With exceptional high-performance VM sizes in the G range, you can easily handle business critical applications such as large relational database servers (SQL Server, MySQL, and so on) or large NoSQL databases (MongoDB, Cloudera Cassandra, and so on).
• H-series: The H-series is designed for high-performance computing and data intensive workloads (for example, molecular modeling and flow dynamics). Optional with high-throughput network interfaces (RDMA).
• Ls-series: The Ls-series is a clone from the GS-series and it is built for low latency storage demands above the offerings of GS-series.
• M-series: The M-series offers the highest number of CPUs (up to 128 vCPUs) and the largest memory (up to 2.0 TB) for the virtual machine at the Azure platform. This is ideal for extremely large databases or other high end applications that require a high CPU count and large amounts of memory.
• N-series: The N-series is not defined by factors such as CPU or memory, but by the possibility to use GPUs (the processors of the graphics card) as an additional power factor. In the form of the GPU, additional computing capacity is provided, whereby the GPU generally operates faster than the CPU in highly parallelizable program sequences (high data parallelism), and therefore, a simple way is sought to supplement the computing performance of CPUs by the computing performance of GPUs. The Compute Unified Device Architecture (CUDA) and/or Open Computing Language (OpenCL) technologies are used for this purpose. The use of the GPU performance is particularly suitable for computer- and graphics-intensive workloads and supports you in scenarios such as high-end visualization, deep learning, and predictive analytics.

As you can see, there are some Azure series that have an s within the name. Those series VMs use SSDs and Azure premium storage as the primary storage type for data and operating systems. They should be chosen for a regular storage performance over 500 IOPS.

Is that all? No; in order to work with VMs as easily as possible, there are also over 4,000 prefabricated images available in the Azure Marketplace.

Now, I've been talking about Azure VMs all the time. Nevertheless, the question remains open: what is behind this offer? Since the answer to the question is very complex, I will divide it into several parts. Before I start, however, I have an important note: the following descriptions are valid for all Azure VMs and this is independent from the selected operating system (Linux or Windows). If there are any differences, I will tell you.