The App Engine standard environment is based on container instances running on Google's infrastructure. Containers are preconfigured with one of several available runtimes. The standard environment makes it easy to build and deploy an application that runs reliably even under heavy load and with large amounts of data. Applications run in a secure, sandboxed environment, allowing the standard environment to distribute requests across multiple servers and scale servers to meet traffic demands. Your application runs within its own secure, reliable environment that is independent of the hardware, operating system, or physical location of the server. ## Standard environment languages and runtimes The standard environment supports the following languages: [Go](https://docs.cloud.google.com/appengine/docs/standard/go/runtime) [Java](https://docs.cloud.google.com/appengine/docs/standard/java-gen2/runtime) [Node.js](https://docs.cloud.google.com/appengine/docs/standard/nodejs/runtime) [PHP](https://docs.cloud.google.com/appengine/docs/standard/php-gen2/runtime) [Python](https://docs.cloud.google.com/appengine/docs/standard/python3/runtime) [Ruby](https://docs.cloud.google.com/appengine/docs/standard/ruby/runtime)
## Instance classes The *instance class* determines the amount of memory and CPU available to each instance, the amount of [free quota](https://docs.cloud.google.com/appengine/docs/standard/quotas#Instances), and the [cost per hour](https://cloud.google.com/appengine/pricing#standard_instance_pricing) after your app exceeds the free quota. For all runtime generations, the memory limit includes the memory your app uses along with the memory that the runtime itself needs to run your app. The Java runtimes use more memory to run your app than other runtimes. To override the default instance class, use the [`instance_class` setting](https://docs.cloud.google.com/appengine/docs/standard/python3/config/appref#instance_class) in your app's `app.yaml` file. | Instance Class | Memory Limit | CPU Limit | Supported Scaling Types | |---|---|---|---| | F1 (default) | 384 MB | 600 MHz | automatic | | F2 | 768 MB | 1.2 GHz | automatic | | F4 | 1536 MB | 2.4 GHz | automatic | | F4_1G | 3072 MB | 2.4 GHz | automatic | | B1 | 384 MB | 600 MHz | manual, basic | | B2 (default) | 768 MB | 1.2 GHz | manual, basic | | B4 | 1536 MB | 2.4 GHz | manual, basic | | B4_1G | 3072 MB | 2.4 GHz | manual, basic | | B8 | 3072 MB | 4.8 GHz | manual, basic | The CPU values and limits reported in the instance class table don't reflect a fixed clock speed in the CPU. Instead, they represent the instance's allocated relative compute power or performance tier on the [shared-core](https://docs.cloud.google.com/compute/docs/general-purpose-machines#n1-shared-core) instance type. System tools might report the total physical memory of the underlying host machine. This is different from the instance's enforced memory limit, which is the maximum memory available to the instance's isolated sandbox environment. Exceeding this "Memory Limit", not the host's total RAM, might cause performance issues. > [!NOTE] > **Important:** When you [view your bill](https://docs.cloud.google.com/billing/docs/how-to/reports), you will not see the names of the individual instance classes in your billing line items. Instead, you see instance hours from the "B" classes reported as "Backend Instances", and instance hours from the "F" classes reported as "Frontend Instances". The bill will apply the appropriate multiple of instance hours for each instance class you use. For example, if you use an F4 instance for one hour, you see "Frontend Instance" billing for four instance hours at the F1 rate. ## Quotas and limits The standard environment gives you 1 GiB of data storage and traffic for free, which can be increased by enabling paid applications. However, some features impose limits unrelated to quotas to protect the stability of the system. For more details on quotas, including how you can edit them to suit your needs, see [Quotas](https://docs.cloud.google.com/appengine/docs/standard/quotas).