DTU is a bit difficult, as it can be described as an object, but it is not actually a real object. DTUs are performance units to which a certain percentage of the total performance of the database server is allocated in CPU, memory, and read or write rates. The offered performance levels contain between 5 DTU (in the Basic service level) and 4,000 DTUs (in the Premium service level P15).

The larger the number of DTUs, the greater the performance of the database. Another criterion for the selection of a performance level is the maximum size of the database.

Also, the maximum size, that can reach the database depends on the selected performance level. The maximum size of the database per level is:

• Basic: 2 GB
• Standard (S0 – S12): 250 GB
• Premium (P1 – P6): 500 GB
• Premium (P11 + P15): 4 TB
• Premium RS: 500 GB

Is that all now? No, also the number of simultaneously concurrent requests (maximum concurrent workers), the number of concurrent logins (maximum concurrent logins), and the number of concurrent sessions (maximum sessions) are limited per level.

As you can see, performance depends on many factors when using Azure services. Here are the most important ones:

• CPU selection (number of CPUs, number of cores, processor type)
• RAM
• Memory (maximum size)
• Memory for temporary data (maximum size, SSD or HDD)
• Use of the GPU (graphics card processor)
• Latency
• Input/output operations per second (IOPS)