# How Do I Select an Image?

When creating an ECS or BMS, you can select an image based on the following factors:

- Region and AZ
- Image Type
- OS

#### Region and AZ

An image is a regional resource. You cannot use an image to create an instance in a different region. For example, when creating an instance in region A, you can only select an image that is already in region A. For more regions, see Region and AZ.

#### Image Type

Images are classified into public images, private images, and shared images. A private image can be a system disk image, data disk image, or full-ECS image. For details, see What Is Image Management Service?

#### OS

When selecting an OS, consider the following factors:

- Architecture types

  System Architecture | Applicable Memory | Constraints
  --- | --- | ---

  32-bit

  Smaller than 4 GB

  - If the instance memory is greater than 4 GB, a 32-bit OS cannot be used.
  - A 32-bit OS only allows addressing within a 4 GB memory range. An OS with more than 4 GB memory cannot be accessed.

  64-bit | 4 GB or larger | If your application requires more than 4 GB of memory or the memory may need to be expanded to more than 4 GB, use a 64-bit OS.

- OS types

  OS Type | Applicable Scenario | Constraints
  --- | --- | ---

  Windows

  - Programs developed for Windows (for example, .NET).
  - Databases such as SQL Server. (You need to install the database.)

  The system disk must be at least 1 GB, and there must be at least 1 GB of memory.

  Linux

  - High-performance server applications (for example, Web) and working with common programming languages such as PHP and Python.
  - Databases such as MySQL. (You need to install the database.)

  The system disk must be at least 1 GB, and there must be at least 512 MB of memory.

Parent topic: Image Consulting