Azure provides just over 120 different configurations that you can choose from these are called Instant sizes. Not every region of the world contains every instance size. That 120 plus virtual machine sizes get categorized into what are called instance types
General Purpose Instance
These are for general purpose with balanced CPU to memory ratio consisting of the B, D, DS, A and DC series. The B series are for development use.
Compute Optimised – High CPU to Memory ratio
These consists of higher powered CPU compared to memory and consists of the F and FS series.
Memory Optimised – High Memory to CPU ratio
These consists of higher memory compared to CPU power and consists of the E, ES, M, G, GS, D* and DS* series. The D series is typically for general purpose, but at higher levels it is considered memory optimised. This can be useful for database servers, caching servers and for any analytics that does a lot of work in memory
Storage Optimised – High disk throughput and IO
These are useful where high throughput and high IO is required on the local disk such as database servers. This consists of the LS series where the S stands for SSD.
GPU – Graphic rendering
When we have requirements around modelling and machine learning where the GPU is the king, the GPU optimised VM are more suitable. This consists of the N series (NV, NC and ND).
High Performance – Fastest & most powerful
This is the H series where we really require the most powerful VMs. These are placed on a special network called the R DMA.