# Use the Amazon Common Runtime (Amazon CRT) extension in the SDK for PHP
<a name="guide_crt"></a>

The [Amazon CRT libraries](https://docs.amazonaws.cn//sdkref/latest/guide/common-runtime.html) provide basic functionality with good performance and minimal footprint for several Amazon SDKs. This topic discusses when the Amazon CRT is used by the SDK for PHP and how to install the Amazon CRT extension.

## When you need the Amazon CRT extension installed
<a name="php-crt-uses"></a>

The SDK for PHP uses the authorization and checksum functionality of the Amazon CRT libraries. The Amazon CRT extension is required when you work with:
+ [Amazon S3 Multi-Region Access Points](s3-multi-region-access-points.md)
+ [Amazon EventBridge global endpoints](eventbridge-examples.md)
+ [A CRC-32C checksum algorithm in Amazon Simple Storage Service (Amazon S3)](s3-checksums.md)

If you use a feature listed above and the Amazon CRT extention is not installed in your PHP environment, the SDK for PHP will report an error message and remind you to install the extension.

## Install the Amazon Common Runtime (Amazon CRT) extension
<a name="php-crt-install"></a>

Instructions on how to install the Amazon CRT extension are available on the main page of the [GitHub repository for the aws-crt-php](https://github.com/awslabs/aws-crt-php#aws-common-runtime-php-bindings).